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During plantation slavery, African rice (Oryza glaberrima Steud.) was widely cultivated in the Americas but was soon replaced by Asian rice (Oryza sativa L.). Maroons, descendants of Africans who escaped slavery in Suriname and French Guiana, continue to cultivate African rice. Genomic research linked this rice to an O. glaberrima variety in the Ivory Coast. Based on interviews with 99 Maroon farmers, of whom 23 cultivate black rice, we describe its diverse uses as (ceremonial) food, offerings, spiritual medicine, and its role during funerals. Maroon oral history accounts on the origin of black rice differ among and within communities: enslaved women brought it from Africa or took it from the plantations where they worked; escaped slaves found it in the savanna; or ancestors encountered it in interior swamps. These multiple and sometimes contradictory accounts of the origins of black rice are related to the diverse ethnic and geographical backgrounds of the Africans brought as slaves to Suriname and their different histories with the crop after marronage. Various characteristics of black rice, including its ability to compete with weeds and grow on poor soils, its shattering seeds, and its visibility to birds explain how this African domesticate survived in the wild in the Amazonian forest. The migration of Maroons to cities, their engagement in gold mining, and their evangelization may lead to the loss of black rice knowledge and practices. [ABSTRACT FROM AUTHOR]

The abundant genetic variation harbored by wild rice (Oryza rufipogon) has provided a reservoir of useful genes for rice breeding. However, the genome of wild rice has not yet been comprehensively assessed. Here, we report the haplotype-resolved gapless genome assembly and annotation of wild rice Y476. In addition, we develop two sets of chromosome segment substitution lines (CSSLs) using Y476 as the donor parent and cultivated rice as the recurrent parents. By analyzing the gapless reference genome and CSSL population, we identify 254 QTLs associated with agronomic traits, biotic and abiotic stresses. We clone a receptor-like kinase gene associated with rice blast resistance and confirm its wild rice allele improves rice blast resistance. Collectively, our study provides a haplotype-resolved gapless reference genome and demonstrates a highly efficient platform for gene identification from wild rice. Genetic variation present in wild rice is a reservoir of useful genes for rice breeding. Here, the authors report the haplotype-resolved gapless genome assembly of wild rice, the development of two sets of chromosome segment substitution lines, and the cloning of a blast resistance gene originated from wild rice. [ABSTRACT FROM AUTHOR]

Compared to japonica, the lower genetic transformation efficiency of indica is a technical bottleneck for rice molecular breeding. Specifically, callus browning frequently occurs during the culture of the elite indica variety 93-11, leading to poor culturability and lower genetic transformation efficiency. Here, 67 QTLs related to culturability were detected using 97 introgression lines (designated as 9DILs) derived from Dongxiang common wild rice (DXCWR, Oryza rufipogon Griff.) with 93-11 genetic background, explaining 4% ~12% of the phenotypic variations. The QTL qCBT9 on chromosome 9 was a primary QTL for reducing callus browning derived from DXCWR. Five 9DILs with light callus browning and high differentiation were screened. We evaluated the callus browning index (CBI) of 100 F2 population crossed of 93-11 and 9DIL71 and the recombinant plants screened from 3270 individuals. The qCBT9 was delimited to a ~148kb region between the markers X16 and X23. RNA-seq analysis of DEGs between 9DIL71 and 93-11 showed three upregulated DEGs (Os09g0526500, Os09g0527900, Os09g0528200,) and three downregulated DEGs (Os09g0526700, Os09g0526800, Os09g0527700) were located in the candidate region of qCBT9. Furthermore, callus browning may be involved in cell senescence and death caused by oxidative stress. The differentiation of indica and japonica in this region suggested that qCBT9 was possibly a vital QTL contributed to better culturability of japonica. Our results laid a foundation for further cloning of the gene for reduced callus browning in O. rufipogon, and also provided a new genetic resource and material basis for improving the culturability and genetic transformation efficiency of cultivated rice. [ABSTRACT FROM AUTHOR]

Weedy rice is a major problem in paddy fields around the world. It is well known that weedy rice appears to grow faster and mature earlier than cultivated rice. It is possible that differences in the root microbial genetics are correlated with this characteristic. This study incorporated 16S rRNA amplicon sequencing to study the microbial composition in the rhizosphere and endosphere of rice root. No significant difference was found between the microbiota associated with weedy and cultivated rice lines grown in the same field. It was found that the endosphere had less microbial diversity compared to the rhizosphere. The major groups of bacteria found in the endosphere are from the phylum Proteobacteria, Myxococcota, Chloroflexota, and Actinobacteria. In addition, by analyzing the microbiome of japonica rice grown in the field in a temperate climate, we found that despite differences in genotype and location, some bacterial taxa were found to be common and these members of the putative rice core microbiome can also be detected by in situ hybridization. The delineation of a core microbiome in the endosphere of rice suggests that these bacterial taxa might be important in the life cycle of a wide range of rice types. [ABSTRACT FROM AUTHOR]

The key genes BADH2, GBSS1, GBSS2, and HIS1 regulate the fragrance, starch synthesis, and herbicide resistance in rice. Although the molecular functions of four genes have been investigated in the Oryza sativa species, little is known regarding their evolutionary history in the Oryza genus. Here, we studied the evolution of four focal genes in 10 Oryza species using phylogenetic and syntenic approaches. The HIS1 family underwent several times of tandem duplication events in the Oryza species, resulting in copy number variation ranging from 2 to 7. At most one copy of BADH2, GBSS1, and GBSS2 orthologs were identified in each Oryza species, and gene loss events of BADH2 and GBSS2 were identified in three Oryza species. Gene transfer analysis proposed that the functional roles of GBSS1 and GBSS2 were developed in the Asian and African regions, respectively, and most allelic variations of BADH2 in japonica rice emerged after the divergence between the Asian and African rice groups. These results provide clues to determine the origin and evolution of the key genes in rice breeding as well as valuable information for molecular breeders and scientists to develop efficient strategies to simultaneously improve grain quality and yield potential in rice. [ABSTRACT FROM AUTHOR]

Rice is cultivated and consumed worldwide. It belongs to genus 'Oryza' with about 21 wild relatives and eight identified genomes which makes it accessible to the huge pool of genetic resources. The rice crop can be distressed by various biotic and abiotic stressors that affect its productivity. Brown planthoppers (BPH) are major pests of different persistent biotypes in different regions. Several major and minor genes and quantitative trait loci (QTLs) regulate BPH resistance, a composite character. These genes/QTLs employ different resistance mechanisms and may be specific to each biotype. 22 of the 44 BPH genes are found in the wild cousins of rice. Several genes have been discovered, cloned, functionally assessed, and introduced into various lines. Most of the identified genes have not been functionally studied rendering their mechanisms to remain unknown. With the discovery that BPH-1 could not provide protection against Biotype 2, there were concerns about a major plant hopper outbreak. To avoid such a scenario, genes from various sources and different resistance mechanisms are being explored. [ABSTRACT FROM AUTHOR]

Aromatic rice cultivars fetch premium price globally. Jeerakasala and Gandhakasala are the two most important and popular tropical scented rice cultivars of Kerala with GI (geographical indication) tags. Reliable procedures are essential and need of the hour for preventing adulteration in aromatic rice cultivars. Molecular technologies using polymerase chain reaction based microsatellite markers are the most reliable and efficient, compared to morphological and biochemical strategies. In this study, we aimed to identify simple sequence repeats (SSR) markers to distinguish between aromatic and non-aromatic rice cultivars at the Regional Agricultural Research Station, Pattambi, Kerala, India. Two aromatic (Gandhakasala and Jeerakasala) and two non-aromatic popular rice cultivars (Jyothi and Aathira) of Kerala, were used for the study. In the bulked line analysis using five SSR markers, RM163, RM202, and RM342 exhibited polymorphism between the aromatic and non-aromatic bulks. In addition, these three SSR markers exhibited polymorphism in individual genotyping. Hence these SSR markers are promising for discriminating between aromatic and non-aromatic tropical rice genotypes and for preventing adulteration. [ABSTRACT FROM AUTHOR]

Breeding for "weed competitive" cultivars is a prioritized goal under direct seeded rice (DSR) conditions for achieving higher grain yields. Early seedling vigour (ESV) is an imperative trait that imparts weed competitiveness through initial rapid growth and uniform crop establishment. African rice species Oryza glaberrima has been recognised as potential donors for weed competitive traits due to their early vegetative vigour. In the present study, 29 accessions of O. glaberrima were evaluated for early seedling vigour traits under laboratory and DSR conditions. Seedling vigour index-I and II estimated from the paper roll method under laboratory condition revealed that six O. glaberrima accessions (EC861796, EC861801, EC861804, EC861814, EC861819 and EC861820) had higher/similar seedling vigour indices than high vigour check Sabita. In addition, during Kharif 2017 and Rabi 2018, O. glaberrima accessions were phenotyped for nine ESV traits, e.g. seedling height, number of leaves/tillers, leaf area, shoot fresh/dry weight, absolute growth rate, specific leaf area and crop growth rate under DSR condition. Significant genetic variation and genotype × environment interaction was observed for ESV traits under DSR condition. The heritability estimates for ESV traits were ranging from low to high, indicating complex inheritance of the trait. The study identified six accessions of O. glaberrima (EC861787, EC861790, EC861792, EC861795, EC861819 and EC861820) as promising accessions with early seedling vigour based on mean performance in both seasons under direct seeded rice condition. Thus, our study demonstrated inherent nature of early seedling vigour in O. glaberrima and these promising accessions could be exploited for breeding weed-competitive rice cultivars. [ABSTRACT FROM AUTHOR]

Oryza coarctata (2n = 4X = 48, KKLL) is an allotetraploid, undomesticated relative of rice and the only species in the genus Oryza with tolerance to high salinity and submergence. Therefore, it contains important stress and tolerance genes/factors for rice. The initial draft genome published was limited by data and technical restrictions, leading to an incomplete and highly fragmented assembly. This study reports a new, highly contiguous chromosome-level genome assembly and annotation of O. coarctata. PacBio high-quality HiFi reads generated 460 contigs with a total length of 573.4 Mb and an N50 of 23.1 Mb, which were assembled into scaffolds with Hi-C data, anchoring 96.99% of the assembly onto 24 chromosomes. The genome assembly comprises 45,571 genes, and repetitive content contributes 25.5% of the genome. This study provides the novel identification of the KK and LL genome types of the genus Oryza, leading to valuable insights into rice genome evolution. The chromosome-level genome assembly of O. coarctata is a valuable resource for rice research and molecular breeding. [ABSTRACT FROM AUTHOR]

Salt stress causes significant reductions in rice production worldwide; thus, improving salt tolerance is a promising approach to meet the increasing food demand. Wild rice germplasm is considered to be a valuable genetic resource for improving rice cultivars. However, information regarding the improvement of salt tolerance in cultivated rice using wild rice genes is limited. Given that Dongxiang wild rice (Oryza rufipogon Griff) is characterized by strong salt stress tolerance, in this study, to elucidate the molecular genetic mechanisms of salt-stress tolerance in Dongxiang wild rice, a backcross inbred line (BIL) population derived from an interspecific cross between Xieqingzao B (Oryzasativa L.) and an accession of Dongxiang wild rice was used for genetic linkage map construction and quantitative trait locus (QTL) mapping associated with salt tolerance at the seedling stage. The results showed that a linkage map consisting of 132 markers was constructed. Through evaluating the salt tolerance of 224 BILs at the seedling stage, a total of 11 QTLs related to salt tolerance were identified on chromosomes 2, 3, 4, 5, 7, 9, 11, and 12, with individual QTLs explaining 2.4–12.5% of phenotypic variance. All of the additive alleles in the QTLs were derived from O. rufipogon. In these QTLs, we found that 4 QTLs qDXWRST-1, qDXWRST-4, qDXWRST-9, and qDXWRST-10 did not overlap with QTLs previously reported for salt tolerance at the seedling stage of cultivated rice and could be considered as novel salt tolerance loci compared with cultivated rice. In addition, qDXWRST-1 and qDXWRST-9 were considered as new and unique loci for salt tolerance at seedling stage in Dongxiang wild rice. Overall, the favorable O. rufipogon-derived QTLs identified in the present study will provide new genetic resources for improving the resistance of cultivated rice against salinity stress using molecular breeding strategies in the future. [ABSTRACT FROM AUTHOR]

Resistant rice varieties are considered to be a potential alternative for controlling the plant-parasitic nematode Meloidogyne graminicola in the field due to their joint economic and environmental sustainability features. However, the emergence of virulent pathogen forms threatens natural resistance durability. In this study, we isolated a virulent M. graminicola population from a naturally infested field in Cambodia that overcomes the resistance of the Oryza sativa Zhonghua 11 rice variety. We used molecular (internal transcribed spacer of rDNA and mitochondrial markers) and morphological approaches to unequivocally identify and confirm the species identification. Few intraspecific variabilities in traits between the virulent pathotype and several avirulent pathotypes were found. Remarkably, histological analysis showed the absence of a hypersensitive response (HR) on root cells surrounding the nematode in the "virulent pathotype–Zhonghua 11" interaction. In addition, the virulent pathotype reproduced to a significant extent in two other Oryza sativa varieties known to be resistant to M. graminicola. However, this virulent population was unable to overcome the previously described resistance in three Oryza glaberrima varieties. We concluded that the virulent M. graminicola pathotype isolated in this study could compromise rice breeding programs based on the sole use of known resistant O. sativa gene pools. The identification of this virulent pathotype should provide the genetic resources needed to study the molecular mechanisms that may enable M. graminicola to bypass HR resistance. [ABSTRACT FROM AUTHOR]

Rice panicle architecture is directly associated with grain yield and is also the key target in high-yield rice breeding program. In this study, three BC6F2 segregation populations derived from the crosses between two accessions of Oryza meridionalis and a O. sativa spp. japonica cultivar Dianjingyou 1, were employed to map QTL for panicle architecture. Three QTL, EP4.2, DEP7 and DEP8 were identified and validated using substitution mapping strategy on chromosome 4, 9 and 8, respectively. The three QTL showed pleiotropic phenotype on panicle length (PL), grain number per panicle (GNPP), number of primary branches (NPB), number of secondary branches (NSB), and grain width. DEP7 and DEP8 showed yield-enhancing potential by increasing GNPP, NPB and NSB, while EP4.2 exhibited wide grain, short stalk and panicle which can improve plant and panicle architecture, too. Moreover, epistatic interaction for PL was detected between EP4.2 and DEP7, and epistatic analysis between DEP7 and DEP8 for GNPP and NPB also revealed significant two QTL interactions. The result would help us understand the molecular basis of panicle architecture and lay the foundation for using these three QTL in rice breeding. [ABSTRACT FROM AUTHOR]

Panicle structure is one of the most important agronomic traits directly related to rice yield. This study identified a rice mutant basal primary branch 1 (bpb1), which exhibited a phenotype of reduced panicle length and arrested basal primary branch development. In addition, lignin content was found to be increased while cellulose content was decreased in bpb1 young panicles. Map-based cloning methods characterized the gene BPB1, which encodes a peptide transporter (PTR) family transporter. Phylogenetic tree analysis showed that the BPB1 family is highly conserved in plants, especially the PTR2 domain. It is worth noting that BPB1 is divided into two categories based on monocotyledonous and dicotyledonous plants. Transcriptome analysis showed that BPB1 mutation can promote lignin synthesis and inhibit cellulose synthesis, starch and sucrose metabolism, cell cycle, expression of various plant hormones, and some star genes, thereby inhibiting rice panicle length, resulting in basal primary branch development stagnant phenotypes. In this study, BPB1 provides new insights into the molecular mechanism of rice panicle structure regulation by BPB1 by regulating lignin and cellulose content and several transcriptional metabolic pathways. [ABSTRACT FROM AUTHOR]

Understanding and exploiting genetic diversity is a key factor for the productive and stable production of rice. Here, we utilize 73 high-quality genomes that encompass the subpopulation structure of Asian rice (Oryza sativa), plus the genomes of two wild relatives (O. rufipogon and O. punctata), to build a pan-genome inversion index of 1769 non-redundant inversions that span an average of ~29% of the O. sativa cv. Nipponbare reference genome sequence. Using this index, we estimate an inversion rate of ~700 inversions per million years in Asian rice, which is 16 to 50 times higher than previously estimated for plants. Detailed analyses of these inversions show evidence of their effects on gene expression, recombination rate, and linkage disequilibrium. Our study uncovers the prevalence and scale of large inversions (≥100 bp) across the pan-genome of Asian rice and hints at their largely unexplored role in functional biology and crop performance. Pan-genomes provide useful resources for evolutionary studies, functional genomics and breeding of cultivated plants. Here, the authors report a new rice pan-genome including 73 Asian rice and two wild relatives (Oryza rufipogon and O. punctata), and reveal the prevalence and scale of large inversions across the pan-genome. [ABSTRACT FROM AUTHOR]

As climate change intensifies, the development of resilient rice that can tolerate abiotic stresses is urgently needed. In nature, many wild plants have evolved a variety of mechanisms to protect themselves from environmental stresses. Wild relatives of rice may have abundant and virtually untapped genetic diversity and are an essential source of germplasm for the improvement of abiotic stress tolerance in cultivated rice. Unfortunately, the barriers of traditional breeding approaches, such as backcrossing and transgenesis, make it challenging and complex to transfer the underlying resilience traits between plants. However, de novo domestication via genome editing is a quick approach to produce rice with high yields from orphans or wild relatives. African wild rice, Oryza longistaminata, which is part of the AA-genome Oryza species has two types of propagation strategies viz. vegetative propagation via rhizome and seed propagation. It also shows tolerance to multiple types of abiotic stress, and therefore O. longistaminata is considered a key candidate of wild rice for heat, drought, and salinity tolerance, and it is also resistant to lodging. Importantly, O. longistaminata is perennial and propagates also via rhizomes both of which are traits that are highly valuable for the sustainable production of rice. Therefore, O. longistaminata may be a good candidate for de novo domestication through genome editing to obtain rice that is more climate resilient than modern elite cultivars of O. sativa. [ABSTRACT FROM AUTHOR]

Plant precursor miRNAs (pre-miRNA) have conserved evolutionary footprints that correlate with mode of miRNA biogenesis. In plants, base to loop and loop to base modes of biogenesis have been reported. Conserved structural element(s) in pre-miRNA play a major role in turn over and abundance of mature miRNA. Pre-miR396c sequences and secondary structural characteristics across Oryza species are presented. Based on secondary structure, twelve Oryza pre-miR396c sequences are divided into three groups, with the precursor from halophytic Oryza coarctata forming a distinct group. The miRNA-miRNA* duplex region is completely conserved across eleven Oryza species as are other structural elements in the pre-miRNA, suggestive of an evolutionarily conserved base-to-loop mode of miRNA biogenesis. SNPs within O. coarctata mature miR396c sequence and miRNA* region have the potential to alter target specificity and association with the RNA-induced silencing complex. A conserved SNP variation, rs10234287911 (G/A), identified in O. sativa pre-miR396c sequences alters base pairing above the miRNA-miRNA* duplex. The more stable structure conferred by the 'A10234287911' allele may promote better processing vis-à-vis the structure conferred by 'G10234287911' allele. We also examine pri- and pre-miR396c expression in cultivated rice under heat and salinity and their correlation with miR396c expression. [ABSTRACT FROM AUTHOR]

Plant breeding efforts to boost rice productivity have focused on developing a haploid development pipeline. CENH3 gene has emerged as a leading player that can be manipulated to engineer haploid induction system. Currently, allele mining for the OsCENH3 gene was done by PCR-based resequencing of 33 wild species accessions of genus Oryza and in silico mining of alleles from pre-existing data. We have identified and characterized CENH3 variants in genus Oryza. Our results indicated that the majority CENH3 alleles present in the Oryza gene pool carry synonymous substitutions. A few non-synonymous substitutions occur in the N-terminal Tail domain (NTT). SNP A/G at position 69 was found in accessions of AA genome and non-AA genome species. Phylogenetic analysis revealed that non-synonymous substitutions carrying alleles follow pre-determined evolutionary patterns. O. longistaminata accessions carry SNPs in four codons along with indels in introns 3 and 6. Fifteen haplotypes were mined from our panel; representative mutant alleles exhibited structural variations upon modeling. Structural analysis indicated that more than one structural variant may be exhibited by different accessions of single species (Oryza barthii). NTT allelic mutants, though not directly implicated in HI, may show variable interactions. HI and interactive behavior could be ascertained in future investigations. [ABSTRACT FROM AUTHOR]

Crop breeding programs can improve traits associated with desirable phenotypic characteristics to different local environmental conditions. In rice, such improvements were achieved depending on genetic diversity among local populations. Here, we examined whether differences in traits of elite varieties are due to genetic differences and from what the genetic differences are derived. Previously, we identified one quantitative trait locus (QTLs) associated with heading date, i.e., the quantitative trait locus for days to heading on chromosome 3 (qDTH3). Using 592 plants of the F2 generation, fine mapping narrowed the qDTH3 locus down to a 158-kb region of the corresponding rice reference genome. Based on the genome sequences of a 656-kb region including the qDTH3 locus among four Oryza species collections, we propose the historic evolutionary process of cultivated rice, considering nucleotide polymorphisms and intrapopulation recombination. Phenotypic differences in qDTH3 in elite varieties may be derived from a different lineage split from the ancestor. [ABSTRACT FROM AUTHOR]

Bcl-2-associated anthogenes (BAGs), chaperone regulators are known to regulate programmed cell death in plants. In the present study, we have identified eight BAG genes in the rice (Oryza sativa) genome. Subsequently, to understand the evolution, 78 BAG homologs were identified in other nine Oryza species. In addition to the signature ubiquitin-like domain, an additional conserved sequence of 12 amino acids was found in all the class I BAG genes except few exceptions in wild species. A significantly variable number of BAG genes was identified in different Oryza species indicates the expansion of BAG genes due to segmental duplication. Based on whole genome resequencing information available for 4726 rice genotypes, haplotype diversity and the functional effect of variations in BAG genes were predicted. Transcriptomic analyses further suggested the multifunctional roles of BAG genes during both developmental and defense response in Oryza species. Differential expression of BAG genes particularly BAG3 and BAG5 was observed under heavy metal stress. Similarly, higher expression of OsBAG1 and OsBAG2 were found in resistant rice cultivar in response to Magnaporthe oryzae infection and OsBAG2 showed upregulation in response to Xanthomonas oryzae infection as well. A similar expression of BAG genes was observed in the qRT-PCR analysis. Furthermore, heterologous transient expression of OInBAG6 protein tagged with yellow fluorescent protein in tobacco leaves showed the subcellular localization in both nucleus and plasma membrane. This study will help to understand the evolution of BAG genes and their role in cell death under stress conditions in rice. [ABSTRACT FROM AUTHOR]

Seeds are continuously exposed to a wide variety of microorganisms in the soil. In addition, seeds contain large amounts of carbon and nitrogen sources that support initial growth after germination. Thus, seeds in the soil can easily promote microbial growth, and seeds are susceptible to decay. Therefore, seed defense against microorganisms is important for plant survival. Seed-microbe interactions are also important issues from the perspective of food production, in seed quality and shelf life. However, seed-microbe interactions remain largely unexplored. In this study, we established a simple and rapid assay system for the antibacterial activity of rice seed crude extracts by colorimetric quantification methods by the reduction of tetrazolium compound. Using this experimental system, the diversity of effects of rice seed extracts on microbial growth was analyzed using Escherichia coli as a bacterial model. We used collections of cultivated rice, comprising 50 accessions of Japanese landraces, 52 accessions of world rice core collections, and of 30 wild Oryza accessions. Furthermore, we attempted to find genetic factors responsible for the diversity by genome-wide association analysis. Our results demonstrate that this experimental system can easily analyze the effects of seed extracts on bacterial growth. It also suggests that there are various compounds in rice seeds that affect microbial growth. Overall, this experimental system can be used to clarify the chemical entities and genetic control of seed-microbe interactions and will open the door for understanding the diverse seed-microbe interactions through metabolites. [ABSTRACT FROM AUTHOR]

Oryza nivara is considered one of the wild progenitors of cultivated Asian rice (O. sativa). An O. nivara (IRGC104443) accession, previously identified as being moderately resistant to rice sheath blight disease, was used as the donor parent to develop an advanced backcross population with the U.S. rice (O. sativa) cultivar, LaGrue, as the recurrent parent. The population was genotyped with 210 DNA markers and a linkage map constructed that spanned 1488.9 cM. Sheath blight (ShB) disease was evaluated in both greenhouse and field conditions. Days to heading (DTHD), plant height (PTHT) and culm (angle) habit (CULMHAB) were recorded because they can confound sheath blight disease ratings under field conditions. Multiple interval mapping identified qShB9 as the ShB-QTL being the source of resistance and the resistance was attributed to the O. nivara allele. The single CULMHAB QTL, qCULMHAB9, was also located in this region but had a different peak suggesting the more open tillering was most likely due to the TILLER ANGLE CONTROL-1 gene which was fine-mapped near the chromosome 9 ShB resistance in other O. sativa populations. The ShB QTL, qShB3-2-mc, identified in the greenhouse study was not verified in the field studies. None of the three DTHD QTL were colocalized with ShB QTL, while the single PTHT QTL was mapped to the region of the semi-dwarf-1 gene for short stature on chromosome 1. Further studies will be undertaken to fine map the qShB9 region and identify linked markers for use in cultivar development. [ABSTRACT FROM AUTHOR]

There is limited information concerning the distribution of mercury in rice, particularly in African rice. The objective was to compare the distribution of total mercury (THg) and methylmercury (MeHg) in African rice (Oryza glaberrima Steud.) and Asian rice (O. sativa L.). It is hypothesized that increased mineral accumulation and greater stress tolerance in O. glaberrima will affect the uptake and distribution of THg and MeHg, compared to O. sativa. Rice varieties from the Republic of Mali, including O. glaberrima (n =1) and O. sativa (n = 2), were cultivated in a greenhouse, in mercury-spiked soil (50 mg/kg) (n =3 replicates/variety). THg and MeHg concentrations were analyzed in the grain (brown rice), and the THg distribution was analyzed using laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS). THg and MeHg concentrations did not differ between O. glaberrima and O. sativa grain. However, in both O. sativa varieties, THg was highly concentrated in the scutellum, which surrounds the embryo and is removed during polishing. Conversely, in O. glaberrima grain, THg was widely distributed throughout the endosperm, the edible portion of the grain. Differences in the THg distribution in O. glaberrima grain, compared to O. sativa, may elevate the risk of mercury exposure through ingestion of polished rice. The novelty of this study includes the investigation of a less-studied rice species (O. glaberrima), the use of a highly sensitive elemental imaging technique (LA-ICP-MS), and its finding of a different grain THg distribution in O. glaberrima than has been observed in O. sativa. [ABSTRACT FROM AUTHOR]

Sheath blight (ShB) caused by Rhizoctonia solani is one of the serious constraints that hamper global rice production. It causes severe yield loss of up to 69% under favorable environmental conditions. The application of chemical fungicides remains the primary approach for the management of this disease. But, overuse of chemical fungicides causes potential health and environmental risk. The use of host plant resistance is a very effective, economic, and sustainable strategy to control sheath blight disease in rice. In this report, we have evaluated 405 accessions of Oryza rufipogon for four ShB-related traits i.e. lesion height (LH), plant height (PH), relative lesion length (RLH), and disease score (DS) during the years 2015, 2016, and 2017. A total of 44,109 high-quality SNP markers on 301 accessions were employed to identify significant marker-trait associations using a genome-wide association study (GWAS). The GWAS analysis revealed a total of 22 significant SNPs associated with the ShB-related traits distributed on all the rice chromosomes except 10 and 12. Among them, eleven were associated with RLH, seven with PH, and one each with LH and DS. The SNPs on chromosomes 3 and 9 were associated with multiple traits. Furthermore, seven ShB resistance loci were also found to be co-localized with previously reported ShB resistance genes/QTLs. These findings provide valuable information to identify key SNPs associated with ShB resistance. Significantly associated SNPs could be used for introgression of ShB resistance traits into rice cultivars using marker-assisted selection. [ABSTRACT FROM AUTHOR]

Heading date is an important trait influencing the grain yield in rice (Oryza sativa L.) and plays a major role in rice breeding programmes. Molecular diversity among 84 rice genotypes belonging to different maturity groups, including cultivars, wild introgression lines and mutants, was investigated using 57 SSR markers linked to heading date. A total of 99 alleles were identified using 42 polymorphic SSRs, with an average of 2.35 alleles per locus. Cluster analysis grouped 84 genotypes into ten major clusters at a genetic similarity of 0.96. The analysis of the genetic structure in the germplasm collection revealed three levels of stratification and the primary division was between O. sativa cultivars and O.nivara introgression lines, followed by a distinction between cultivars and mutants in the O. sativa group. Intra-specific subgroups were detected within cultivated group representing different maturity groups. Breeding programmes involving these diverse genotypes helps in developing high yielding varieties for different maturity groups. [ABSTRACT FROM AUTHOR]

African cultivated rice (Oryza glaberrima Steud) contains many favorable genes for tolerance to biotic and abiotic stresses and F1 hybrids between Asian cultivated rice (Oryza sativa L.) show strong heterosis. However, the hybrids of two species often exhibit hybrid sterility. Here, we identified a male sterility locus qHMS4 on chromosome 4 (Chr.4), which induces pollen semi-sterility in F1 hybrids of japonica rice variety Dianjingyou1 (DJY1) and a near-isogenic line (NIL) carrying a Chr.4 segment from Oryza glaberrima accession IRGC101854. Cytological observations indicated that non-functional pollen grains produced by the hybrids and lacking starch accumulation abort at the late bicellular stage. Molecular genetic analysis revealed distorted segregation in male gametogenesis carrying qHMS4 allele from DJY1. Fine-mapping of qHMS4 using an F2 population of 22,500 plants delimited qHMS4 to a region of 110-kb on the short arm of Chr.4. Sequence analysis showed that the corresponding sequence region in DJY1 and Oryza glaberrima were 114-kb and 323-kb, respectively, and that the sequence homology was very poor. Gene prediction analysis identified 16 and 46 open reading frames (ORFs) based on the sequences of DJY1 and O. glaberrima, respectively, among which 3 ORFs were shared by both. Future map-based cloning of qHMS4 will help to understand the underlying molecular mechanism of hybrid sterility between the two cultivated rice species. [ABSTRACT FROM AUTHOR]

Being one of the most important staple dietary constituents globally, genetic enhancement of cultivated rice for yield, agronomically important traits is of substantial importance. Even though the climatic factors and crop management practices impact complex traits like yield immensely, the contribution of variation by underlying genetic factors surpasses them all. Previous studies have highlighted the importance of utilizing exotic germplasm, landraces in enhancing the diversity of gene pool, leading to better selections and thus superior cultivars. Thus, to fully exploit the potential of progenitor of Asian cultivated rice for productivity related traits, genome wide association study (GWAS) for seven agronomically important traits was conducted on a panel of 346 O. rufipogon accessions using a set of 15,083 high-quality single nucleotide polymorphic markers. The phenotypic data analysis indicated large continuous variation for all the traits under study, with a significant negative correlation observed between grain parameters and agronomic parameters like plant height, culm thickness. The presence of 74.28% admixtures in the panel as revealed by investigating population structure indicated the panel to be very poorly genetically differentiated, with rapid LD decay. The genome-wide association analyses revealed a total of 47 strong MTAs with 19 SNPs located in/close to previously reported QTL/genic regions providing a positive analytic proof for our studies. The allelic differences of significant MTAs were found to be statistically significant at 34 genomic regions. A total of 51 O. rufipogon accessions harboured combination of superior alleles and thus serve as potential candidates for accelerating rice breeding programs. The present study identified 27 novel SNPs to be significantly associated with different traits. Allelic differences between cultivated and wild rice at significant MTAs determined superior alleles to be absent at 12 positions implying substantial scope of improvement by their targeted introgression into cultivars. Introgression of novel significant genomic regions into breeder's pool would broaden the genetic base of cultivated rice, thus making the crop more resilient. [ABSTRACT FROM AUTHOR]

Oryza australiensis is a wild rice native to monsoonal northern Australia. The International Oryza Map Alignment Project emphasises its significance as the sole representative of the EE genome clade. Assembly of the O. australiensis genome has previously been challenging due to its high Long Terminal Repeat (LTR) retrotransposon (RT) content. Oxford Nanopore long reads were combined with Illumina short reads to generate a high-quality ~ 858 Mbp genome assembly within 850 contigs with 46× long read coverage. Reference-guided scaffolding increased genome contiguity, placing 88.2% of contigs into 12 pseudomolecules. After alignment to the Oryza sativa cv. Nipponbare genome, we observed several structural variations. PacBio Iso-Seq data were generated for five distinct tissues to improve the functional annotation of 34,587 protein-coding genes and 42,329 transcripts. We also report SNV numbers for three additional O. australiensis genotypes based on Illumina re-sequencing. Although genetic similarity reflected geographical separation, the density of SNVs also correlated with our previous report on variations in salinity tolerance. This genome re-confirms the genetic remoteness of the O. australiensis lineage within the O. officinalis genome complex. Assembly of a high-quality genome for O. australiensis provides an important resource for the discovery of critical genes involved in development and stress tolerance. [ABSTRACT FROM AUTHOR]

We studied variation in adaptive traits and genetic association to understand the low P responses, including the symbiotic association of arbuscular mycorrhizal (AM) fungal colonization in Oryza species (O. sativa, O. nivara, and O. rufipogon). In the present experiment, we performed the phenotypic variability of the morphometric and geometric traits for P deficiency tolerance and conducted the association studies in GLM and MLM methods. A positive association between the geometric trait of the top-view area and root traits suggested the possibility of exploring a non-destructive approach in screening genotypes under low P. The AMOVA revealed a higher proportion of variation among the individuals as they belonged to different species of Oryza and the NM value was 2.0, indicating possible gene flow between populations. A sub-cluster with superior-performing accessions had a higher proportion of landraces (42.85%), and O. rufipogon (33.3%) was differentiated by four Pup1-specific markers. Association mapping identified seven notable markers (RM259, RM297, RM30, RM6966, RM242, RM184, and PAP1) and six potential genotypes (IC459373, Chakhao Aumbi, AC100219, AC100062, Sekri, and Kumbhi Phou), which will be helpful in the marker-assisted breeding to improve rice for P-deprived condition. In addition, total root surface area becomes a single major trait that helps in P uptake under deficit P up to 33% than mycorrhizal colonization. Further, the phenotypic analysis of the morphometric and geometric trait variations and their interactions provides excellent potential for selecting donors for improving P-use efficiency. The identified potential candidate genes and markers offered new insights into our understanding of the molecular and physiological mechanisms driving PUE and improving grain yield under low-P conditions. [ABSTRACT FROM AUTHOR]

The brown planthopper (Nilaparvata lugens Stål, BPH) is one of the most destructive rice pests worldwide. GXU202 is a germplasm of common wild rice (Oryza rufipogon Griff.) with high resistance to the BPH. In this study, genetic analysis indicated that the BPH-resistant phenotype of GXU202 is controlled by a major gene. Through the combination and comparison of QTL linkage and BSA-seq analyses, a novel gene locus, BPH41, conferring BPH resistance was identified. This gene locus was finely mapped to a 116-kb region delimited by W4-4–3 and W1-6–3 on chromosome 4. The markers D01031 and D01045 showed high accuracy in predicting phenotypes resistant to BPH, suggesting their reliability for marker-assisted selection of BPH41 in breeding BPH-resistant rice varieties. The present identification of BPH41 will establish a foundation for further map-based cloning and functional characterization of the gene. [ABSTRACT FROM AUTHOR]

Pre-harvest sprouting is one of the most serious problems in rice production. Sensitive pre-harvest sprouting causes low seed quality and losses before harvesting. Seed dormancy is one of the most important traits relative to pre-harvest sprouting. In this study, the common wild rice, Oryza rufipogon W630 (strong seed dormancy) was used as a donor to improve the pre-harvest sprouting resistance of O. sativa Indica IR36 (popular cultivar in Asia). Thereafter, 170 backcross recombinant inbred lines (BRILs) at the BC2F8 generation were produced by the single seed descendant method. Their degree of dormancy was assessed and genotype was analyzed using 180 polymorphic SSR markers covering entire chromosomes. Finally, a QTL analysis was conducted by composite interval mapping to identify putative QTLs of seed dormancy and the wild allele effects to the background of typical rice cultivar IR36. Thus, two of 170 BRILs showed stronger seed dormancy compared to recurrent parent IR36. In addition, two putative QTLs for seed dormancy at chromosome 2 and 7 were also found in this population through composite interval mapping. These results indicated the stronger dormancy trait of two BRILs derived from wild rice Oryza rufipogon W630; this trait was also controlled by genetic factors. [ABSTRACT FROM AUTHOR]

Endophytic fungi inhabiting niche environments are novel biocatalyst resources that need to be exploited urgently. In this study, 63 endophytic fungi isolated from Dongxiang wild rice (Oryza rufipogon Griff.) were tested to assess their potentials to transform glycyrrhizin (GL) into glycyrrhetinic acid monoglucuronide (GAMG) or glycyrrhetinic acid (GA), of which 12 strains were shown to have β-d-glucuronidase activity. Based on morphological characteristics and rDNA ITS sequence analysis, the strains S59, L138, L55 and R57 with high GL molar conversion rates (55%, 45%, 65% and 89%) were further identified as Microsphaeropsis arundinis S59, Penicillium rubens L138, Aspergillus flavus L55 and Eupenicillium javanicum R57, respectively. These four strains with four different types of GL conversion processes were identified, i.e., (1) GL → GAMG in M. arundinis S59, (2) GL → GAMG and GA in A. flavus L55, (3) GL → GA in P. rubens L138, and (4) GL → GAMG → GA in E. javanicum R57, in which the bioconversion type (4) is reported for the first time. The study not only provided abundant and diverse β-d-glucuronidase resources that can be used for GL bioconversion, especially for GAMG biosynthesis from endophytic fungi, but also expanded our knowledge of potential roles of endophytes as new biocatalysts in biotransformation. [ABSTRACT FROM AUTHOR]

Main conclusion: Our transcriptomic analysis expanded the repertoire of nitrate-responsive genes/processes in rice and revealed their phenotypic association with root/shoot, stomata, tiller, panicle/flowering and yield, with agronomic implications for nitrogen use efficiency. Nitrogen use efficiency (NUE) is a multigenic quantitative trait, involving many N-responsive genes/processes that are yet to be fully characterized. Microarray analysis of early nitrate response in excised leaves of japonica rice revealed 6688 differentially expressed genes (DEGs), including 2640 hitherto unreported across multiple functional categories. They include transporters, enzymes involved in primary/secondary metabolism, transcription factors (TFs), EF-hand containing calcium binding proteins, hormone metabolism/signaling and methytransferases. Some DEGs belonged to hitherto unreported processes viz. alcohol, lipid and trehalose metabolism, mitochondrial membrane organization, protein targeting and stomatal opening. 1158 DEGs were associated with growth physiology and grain yield or phenotypic traits for NUE. We identified seven DEGs for shoot apical meristem, 66 for leaf/culm/root, 31 for tiller, 70 for heading date/inflorescence/spikelet/panicle, 144 for seed and 78 for yield. RT-qPCR validated nitrate regulation of 31 DEGs belonging to various important functional categories/traits. Physiological validation of N-dose responsive changes in plant development revealed that relative to 1.5 mM, 15 mM nitrate significantly increased stomatal density, stomatal conductance and transpiration rate. Further, root/shoot growth, number of tillers and grain yield declined and panicle emergence/heading date delayed, despite increased photosynthetic rate. We report the binding sites of diverse classes of TFs such as WRKY, MYB, HMG etc., in the 1 kb up-stream regions of 6676 nitrate-responsive DEGs indicating their role in regulating nitrate response/NUE. Together, these findings expand the repertoire of genes and processes involved in genomewide nitrate response in rice and reveal their physiological, phenotypic and agronomic implications for NUE. [ABSTRACT FROM AUTHOR]

Proper anther and pollen development are important for plant reproduction. The plant hormone gibberellin is important for anther development in rice, but its gametophytic functions remain largely unknown. Here, we report the functional and evolutionary analyses of rice gibberellin 3-oxidase 1 (OsGA3ox1), a gibberellin synthetic enzyme specifically expressed in the late developmental stages of anthers. Enzymatic and X-ray crystallography analyses reveal that OsGA3ox1 has a higher GA7 synthesis ratio than OsGA3ox2. In addition, we generate an osga3ox1 knockout mutant by genome editing and demonstrate the bioactive gibberellic acid synthesis by the OsGA3ox1 action during starch accumulation in pollen via invertase regulation. Furthermore, we analyze the evolution of Oryza GA3ox1s and reveal that their enzyme activity and gene expression have evolved in a way that is characteristic of the Oryza genus and contribute to their male reproduction ability. The authors solve the crystal structure of OsGA3ox2 and predict that of OsGA3ox1. These enzymes catalyze the final step in the biosynthesis of gibberellin, one of the plant hormones. Evolutionary analysis combined with the new structure reveal important aspects of the OsGA3ox1's function in plant male reproduction. [ABSTRACT FROM AUTHOR]

Chinese wild rice (Zizania latifolia; family: Gramineae) is a valuable medicinal homologous grain in East and Southeast Asia. Here, using Nanopore sequencing and Hi-C scaffolding, we generated a 547.38 Mb chromosome-level genome assembly comprising 332 contigs and 164 scaffolds (contig N50 = 4.48 Mb; scaffold N50 = 32.79 Mb). The genome harbors 38,852 genes, with 52.89% of the genome comprising repetitive sequences. Phylogenetic analyses revealed close relation of Z. latifolia to Leersia perrieri and Oryza species, with a divergence time of 19.7–31.0 million years. Collinearity and transcriptome analyses revealed candidate genes related to seed shattering, providing basic information on abscission layer formation and degradation in Z. latifolia. Moreover, two genomic blocks in the Z. latifolia genome showed good synteny with the rice phytocassane biosynthetic gene cluster. The updated genome will support future studies on the genetic improvement of Chinese wild rice and comparative analyses between Z. latifolia and other plants. Yan, Yang, Yu, Shang et al. provide a chromosome-level reference genome for Chinese wild rice (Zizania latifolia) along with phylogenetic and transcriptomic analyses. Their results identify candidate genes related to seed shattering and synteny with the rice phytocassane biosynthetic gene cluster. [ABSTRACT FROM AUTHOR]

The analysis of wild rice cell structures, tissues, organs, and other morphological characteristics and the development of identification markers for wild rice are the basis for identifying the origins and evolution of prehistorical rice agriculture. However, contemporary wild rice strains are often subject to gene introgression from domesticated rice cultivated by humans during the evolutionary process, which may affect the accuracy of wild rice identification markers. This means that how to eliminate the effects of gene introgression from domesticated rice and other plants on the identification of origin markers, and the purification of the morphological characteristics of wild rice have become critical in research to identify the origin of rice. In this study, we compared and analysed the phytolith morphologies of three common wild rice species (Oryza rufipogon Griff.) from various habitats and one species of ectopically preserved homozygous common wild rice after six consecutive generations of self-crossing. We found that the morphology of the bulliform phytolith in the homozygous wild rice with reduced domestication gene introgression had three significant differences compared with native wild rice: (1) an overall reduction in size (body length decreased from 41.9 µm in VLnative to 38.6 µm in VLhomozygous); (2) an increase in the proportion of the long-stalked phenotype, with the ratio of B/A decreasing from 1.22±0.47 in B/Anative to 0.92±0.30 in B/Ahomozygous; and (3) a decrease in the number of fish-scale decorations, with the proportion of bulliform phytoliths with ≥9 fish-scale decorations reduced from 53.4% in native wild rice to 37.2% in homozygous wild rice. Thus, this study provides a reliable reference for the identification of rice origins using rice phytolith morphology. [ABSTRACT FROM AUTHOR]

High seed cost due to poor seed yield severely limits the adoption of hybrid rice by farmers. Increasing the out-crossing rate is one of the key strategies to increase hybrid seed production. Out-crossing rate is highly influenced by the size of female floral traits, which capture pollen grains from male donor plants. In the current study, we identified 14 QTLs derived from the perennial wild rice Oryza longistaminata by composite interval mapping for five key floral traits: stigma length (five), style length (three), stigma breadth (two), stigma area (one), and pistil length (three). QTL analysis and correlation studies revealed that these stigma traits were positively correlated and pleiotropic to the stigma length trait. We selected the major-effect QTL qSTGL8.0 conferring long stigma phenotype for further fine mapping and marker-assisted selection. The qSTGL8.0 (~ 3.9 Mb) was fine mapped using newly developed internal markers and was narrowed down to ~ 2.9 Mb size (RM7356–RM256 markers). Further, the flanking markers were validated in a segregating population and in progenies from different genetic backgrounds. The markers PA08-03 and PA08-18 showed the highest co-segregation with the stigma traits. The qSTGL8.0 was introgressed into two cytoplasmic male sterile (CMS) lines, IR58025A and IR68897A, by foreground, background, and trait selection approaches. The qSTGL8.0 introgression lines in CMS backgrounds showed a significantly higher seed setting rate (2.5–3.0-fold) than the original CMS lines in test crosses with their corresponding maintainer lines. The newly identified QTLs especially qSTGL8.0, will be quite useful for increasing out-crossing rate and this will contribute to increase seed production and decrease seed cost. [ABSTRACT FROM AUTHOR]

Background: Drought is global environmental stress that limits crop yields. Plant-associated microbiomes play a crucial role in determining plant fitness in response to drought, yet the fundamental mechanisms for maintaining microbial community stability under drought disturbances in wild rice are poorly understood. We make explicit comparisons of leaf, stem, root and rhizosphere microbiomes from the drought-tolerant wild rice (Oryza longistaminata) in response to drought stress. Results: We find that the response of the wild rice microbiome to drought was divided into aboveground–underground patterns. Drought reduced the leaf and stem microbial community diversity and networks stability, but not that of the roots and rhizospheres. Contrary to the aboveground microbial networks, the drought-negative response taxa exhibited much closer interconnections than the drought-positive response taxa and were the dominant network hubs of belowground co-occurrence networks, which may contribute to the stability of the belowground network. Notably, drought induces enrichment of Actinobacteria in belowground compartments, but not the aboveground compartment. Additionally, the rhizosphere microbiome exhibited a higher proportion of generalists and broader habitat niche breadth than the microbiome at other compartments, and drought enhanced the proportion of specialists in all compartments. Null model analysis revealed that both the aboveground and belowground-community were governed primarily by the stochastic assembly process, moreover, drought decreased 'dispersal limitation', and enhanced 'drift'. Conclusions: Our results provide new insight into the different strategies and assembly mechanisms of the above and belowground microbial community in response to drought, including enrichment of taxonomic groups, and highlight the important role of the stochastic assembly process in shaping microbial community under drought stress. [ABSTRACT FROM AUTHOR]

Aims: Specific soil bacteria can sense and respond to the selective rhizosphere recruitment of root exudates using unique systems of chemotaxis that mediate plant-microbe and microbe-microbe interactions. This study investigates how the bacterial chemotaxis systems have been impacted by selection during the domestication of rice (Oryza species). Methods: Shotgun metagenomic sequencing and 16S rRNA gene amplicon sequencing were performed to investigate the bacterial chemotaxis systems and chemotactic bacteria in the rhizospheres of wild and cultivated rice. Metabolomics analysis was performed to examine the root metabolites of different accessions of rice. Results: The bacterial chemotaxis genes exhibited a higher abundance in the rhizospheres of wild rice than cultivated rice, and that the compositional profile of chemotaxis genes was distinctly different between types of rice. Differential selection of chemotaxis systems was at least partially driven by changes in the metabolite profiles of rice roots that were affected by domestication. A core group of chemotactic bacteria was also identified, and specific chemotactic bacteria were found to function as hub taxa in the rhizosphere bacterial community. Conclusion: The present study provides novel insights into the composition and function of the bacterial chemotaxis systems in the rhizospheres of wild and domesticated rice. It also provides a new perspective on the impact of rice domestication on the assembly of rhizomicrobiome. [ABSTRACT FROM AUTHOR]

As the number of people in the world increases, people's demand for food becomes greater. In order to reduce reliance on pesticides that maintain crop yields, plant disease resistance is gaining increasing attention. As a near-isogenic line with high resistance to bacterial blight, transcriptional regulation of Y73 on disease resistance has aroused our great interest. To comprehend how Y73 plants defend themselves against bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) and how their disease resistance is executed at the transcriptional level, a time series transcriptional profiles of the local leaves and systemic leaves of Y73 and its recurrent parent Dalixiang (DLX) were obtained after inoculation with Xoo strain PXO341. Transcriptome data showed that the differences between incompatible (Y73 to Xoo) and compatible (DLX to Xoo) interactions were greater in the systemic leaves than in the inoculated ones. In contrast to compatible interactions, incompatible interactions were able to generate a sustained systemic acquired resistance (SAR) response, groups of genes like PR3 (chitinase 5) and PR1 had been up-regulated in systemic leaves. These results provide evidence that a robust and sustained SAR response in Y73 plays an important role in its broad-spectrum and high resistance to bacterial blight. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of endophytic bacteria from cultivated (Oryza sativa) and wild rice (Oryza rufipogon) plants and their functional traits related to plant growth promotion. A total of 70 bacterial isolates were characterized by both biochemical and molecular identification methods. Taxonomic classification showed dominance of three major phyla, viz, Firmicutes (57.1%), Actinobacteria (20.0%) and Proteobacteria (22.8%). Screening for in vitro plant growth-promoting activities revealed a hitherto unreported endophytic bacterium from wild rice germplasm, Microbacterium laevaniformans RS0111 with highest indole acetic acid (28.39 ± 1.39 µg/ml) and gibberellic acid (67.23 ± 1.83 µg/ml) producing efficiency. Few other endophytic isolates from cultivated rice germplasm such as Bacillus tequilensis RHS01 showed highest phosphate solubilizing activity (81.70 ± 1.98 µg/ml), while Microbacterium testaceum MKLS01 and Microbacterium enclense MI03 L05 showed highest potassium (53.42 ± 0.75 µg/ml) and zinc solubilizing activity (157.50%). Fictibacillus aquaticus LP20 05 produced highest siderophore (64.8%). In vivo evaluation of plant growth-promoting efficiencies of the isolates showed that Microbacterium laevaniformans RS0111, Microbacterium testaceum MKLS01 and Bacillus tequilensis RHS 01 could increase rice grain yield by 3.4-fold when compared to the control group. This study indicates the potentiality of rice endophytes isolates as an effective bioinoculants. [ABSTRACT FROM AUTHOR]

Chaling common wild rice (Chaling CWR, Oryza rufipogon Griff.) is a kind of germplasm resource which possesses abundant genetic diversity and plays a pivotal role in improving cultivated rice. In this research, we used next-generation sequencing technology to reveal the genome sequence of Chaling CWR and investigate its elite genes. The results showed that the average coverage was 93.99%. 1,743,368 single-nucleotide polymorphism (SNP) and 387,381 insertion and deletion (InDel) variants have been detected in Chaling CWR compared with the Nipponbare genome. The variant density was found to be highest in chromosome 10 and lowest in chromosome 5, with an average density of 467.08 SNPs/100 kb and 109.59 InDels/100 kb across the whole genome. 109,684 non-synonymous SNPs were identified in 14,315 genes, and 26,051 InDels were detected in the coding regions. We further classified these genes based on the protein domains that were involved in host defense mechanisms and in the analysis of 37 NBS-LRRs, 71 LRRs, 136 NB-ARCs, 119 PKs, 19 WRKY transcription factors, and 25 resistant protein genes. Among the putative R-genes, Pish, Pita, Pi25, Pi9, Pi21, Pid2, Pikm, and Xa21 were further identified, as exhibiting high rates of polymorphism. Results from this study provide a foundation for future basic research and marker-assisted breeding of rice resistance. [ABSTRACT FROM AUTHOR]

Background: The rice (Oryza sativa) gene Xa7 has been hypothesized to be a typical executor resistance gene against Xanthomonas oryzae pv. oryzae (Xoo), and has conferred durable resistance in the field for decades. Its identity and the molecular mechanisms underlying this resistance remain elusive. Results: Here, we filled in gaps of genome in Xa7 mapping locus via BAC library construction, revealing the presence of a 100-kb non-collinear sequence in the line IRBB7 compared with Nipponbare reference genomes. Complementary transformation with sequentially overlapping subclones of the BACs demonstrated that Xa7 is an orphan gene, encoding a small novel protein distinct from any other resistance proteins reported. A 27-bp effector binding element (EBE) in the Xa7 promoter is essential for AvrXa7-inducing expression model. XA7 is anchored in the endoplasmic reticulum membrane and triggers programmed cell death in rice and tobacco (Nicotiana benthamiana). The Xa7 gene is absent in most cultivars, landraces, and wild rice accessions, but highly homologs of XA7 were identified in Leersia perrieri, the nearest outgroup of the genus Oryza. Conclusions: Xa7 acts as a trap to perceive AvrXa7 via EBEAvrXa7 in its promoter, leading to the initiation of resistant reaction. Since EBEAvrXa7 is ubiquitous in promoter of rice susceptible gene SWEET14, the elevated expression of which is conducive to the proliferation of Xoo, that lends a great benefit for the Xoo strains retaining AvrXa7. As a result, varieties harboring Xa7 would show more durable resistance in the field. Xa7 alleles analysis suggests that the discovery of new resistance genes could be extended beyond wild rice, to include wild grasses such as Leersia species. [ABSTRACT FROM AUTHOR]

Background: Grain size and weight are important target traits determining grain yield and quality in rice. Wild rice species possess substantial elite genes that can be served as an important resource for genetic improvement of rice. In this study, we identify and validate a novel QTL on chromosome 7 affecting the grain size and weight using introgression lines from cross of Oryza sativa and Oryza minuta. Results: An introgression line 'IL188' has been achieved from a wild species Oryza minuta (2n = 48, BBCC, W303) into O. sativa japonica Nipponbare. The F2 and F2:3 populations derived from a cross between IL188 and Nipponbare were used to map QTLs for five grain size traits, including grain length (GL), grain width (GW), grain length to width ratio (LWR), grain thickness (GT) and thousand grain weight (TGW). A total of 12 QTLs for the five grain traits were identified on chromosomes 1, 2, 3, 6, 7, and 8. The QTL-qGL7 controlling GL on chromosome 7 was detected stably in the F2 and F2:3 populations, and explained 15.09–16.30% of the phenotypic variance. To validate the effect of qGL7, eight residual heterozygous line (RHL) populations were developed through selfing four F2:3 and four F2:4 plants with different heterozygous segments for the target region. By further developing SSR and Indel markers in the target interval, qGL7 was delimited to a ~ 261 kb region between Indel marker Y7–12 and SSR marker Y7–38, which also showed significant effects on grain width and thousand grain weight. Comparing with the reference genome of Nipponbare, stop or frameshift mutations in the exon of the three putative genes LOC_Os07g36830, LOC_Os07g36900 and LOC_Os07g36910 encoding F-box domain-containing proteins may be the candidate genes for qGL7. Scanning electron microscopy analysis of the glume's epidermal cells showed that the cell length and width of NIL-qGL7IL188 was higher than NIL-qGL7Nip, indicating that qGL7 increases grain size and weight by regulating cell expansion. Conclusions: In this study, we detected 12 QTLs regulating grain size and weight using an introgression line from a cross between Oryza sativa and Oryza minuta. Of these loci, we confirmed and delimited the qGL7 to a ~ 261 kb region. Three putative genes, LOC_Os07g36830, LOC_Os07g36900 and LOC_Os07g36910 encoding F-box domain-containing proteins may be the candidate genes for qGL7. These results provide a basis for map-based cloning of the qGL7 gene and useful information for marker assisted selection in rice grain quality improvement. [ABSTRACT FROM AUTHOR]

Key message: we identified a functional chromogen gene C from wild rice, providing a new insight of anthocyanin biosynthesis pathway in indica and japonica. Accumulation of anthocyanin is a desirable trait to be selected in rice domestication, but the molecular mechanism of anthocyanin biosynthesis in rice remains largely unknown. In this study, a novel allele of chromogen gene C, OrC1, from Oryza rufipongon was cloned and identified as a determinant regulator of anthocyanin biosynthesis. Although OrC1 functions in purple apiculus, leaf sheath and stigma in indica background, it only promotes purple apiculus in japonica. Transcriptome analysis revealed that OrC1 regulates flavonoid biosynthesis pathway and activates a few bHLH and WD40 genes of ternary MYB-bHLH-WD40 complex in indica. Differentially expressed genes and metabolites were found in the indica and japonica backgrounds, indicating that OrC1 activated the anthocyanin biosynthetic genes OsCHI, OsF3H and OsANS and produced six metabolites independently. Artificial selection and domestication of C1 gene in rice occurred on the coding region in the two subspecies independently. Our results reveal the regulatory system and domestication of C1, provide new insights into MYB transcript factor involved in anthocyanin biosynthesis, and show the potential of engineering anthocyanin biosynthesis in rice. [ABSTRACT FROM AUTHOR]

Historical sources describe irrigation and intensive agriculture being practiced in lowland Yunnan from at least the first century AD, but so far archaeobotanical remains allowing investigation of this issue have been scarce. Here, we present new archaeobotanical evidence, including macro-botanical and phytoliths results, from the Dian settlement site of Dayingzhuang, with direct AMS radiocarbon dates on two wheat grains falling between 750 and 390 BC. We compare these results with contemporary Dian sites and analyse the agricultural systems in Central Yunnan between the eight and fourth centuries BC. We propose that agriculture was intensified toward the end of the Dian through both multiple cropping seasons and increased evidence for irrigated rice fields. [ABSTRACT FROM AUTHOR]

For breeding of salinity tolerant rice, halophytic species Oryza coarctata is considered as a valuable resource. Non-availability of molecular markers in the species is a major limitation and identification of markers applicable with wider gene pool will be resource-saving. Even after the recent advancement in high throughput genotyping techniques, sequence-tagged microsatellite sites (STMS) markers are considered as valuable resource for pre-breeding, especially when usable for a large number of species. Using a novel bioinformatics pipeline for cross transferable marker identification, whole genome sequences of nine Oryza species were surveyed with 23,499 STMS markers of rice. With this highly reproducible strategy, band sizes or polymorphism prediction among different species is possible before in-vitro validation. Only 359 STMS markers were cross-transferable to O. coarctata and 77 of those were common with O. sativa complex. These core markers were distributed over 11 chromosomes and nearly 76% were located within various genes of Oryza. The markers also showed unique genome specific polymorphism pattern with high levels of inter- and intraspecific variations in "AA" genome and complete absence of intra- or inter-population variations in O. coarctata (KKLL). The numbers of microsatellite motifs and the repeat numbers in different motifs were much lesser in O. coarctata leading to the exceptionally high level of polymorphism with all "AA" genome species. Two markers are also useful for species identification. The hyper-variable markers are effective resource for pre-breeding of O. sativa, O. glaberrima and new rice for Africa involving O. coarctata or any other species of O. sativa complex. [ABSTRACT FROM AUTHOR]

Background: OryzaGenome (http://viewer.shigen.info/oryzagenome21detail/index.xhtml), a feature within Oryzabase (https://shigen.nig.ac.jp/rice/oryzabase/), is a genomic database for wild Oryza species that provides comparative and evolutionary genomics approaches for the rice research community. Results: Here we release OryzaGenome2.1, the first major update of OryzaGenome. The main feature in this version is the inclusion of newly sequenced genotypes and their meta-information, giving a total of 217 accessions of 19 wild Oryza species (O. rufipogon, O. barthii, O. longistaminata, O. meridionalis, O. glumaepatula, O. punctata, O. minuta, O. officinalis, O. rhizomatis, O. eichingeri, O. latifolia, O. alta, O. grandiglumis, O. australiensis, O. brachyantha, O. granulata, O. meyeriana, O. ridleyi, and O. longiglumis). These 19 wild species belong to 9 genome types (AA, BB, CC, BBCC, CCDD, EE, FF, GG, and HHJJ), representing wide genomic diversity in the genus. Using the genotype information, we analyzed the genome diversity of Oryza species. Other features of OryzaGenome facilitate the use of information on single nucleotide polymorphisms (SNPs) between O. sativa and its wild progenitor O. rufipogon in rice research, including breeding as well as basic science. For example, we provide Variant Call Format (VCF) files for genome-wide SNPs of 33 O. rufipogon accessions against the O. sativa reference genome, IRGSP1.0. In addition, we provide a new SNP Effect Table function, allowing users to identify SNPs or small insertion/deletion polymorphisms in the 33 O. rufipogon accessions and to search for the effect of these polymorphisms on protein function if they reside in the coding region (e.g., are missense or nonsense mutations). Furthermore, the SNP Viewer for 446 O. rufipogon accessions was updated by implementing new tracks for possible selective sweep regions and highly mutated regions that were potentially exposed to selective pressures during the process of domestication. Conclusion: OryzaGenome2.1 focuses on comparative genomic analysis of diverse wild Oryza accessions collected around the world and on the development of resources to speed up the identification of critical trait-related genes, especially from O. rufipogon. It aims to promote the use of genotype information from wild accessions in rice breeding and potential future crop improvements. Diverse genotypes will be a key resource for evolutionary studies in Oryza, including polyploid biology. [ABSTRACT FROM AUTHOR]

Five rice accessions belonging to three wild species viz., IRGC99577 (Oryza punctata Kotschy ex Steud.), IRGC105270, IRGC105275 (O. australiensis Domin.), IRGC104646, CR100204 (O. nivara Sharma et Shastry) along with TN1 (susceptible check) and Ptb33 (resistant check) were used to study antixenosis and the role of biophysical factors in imparting resistance to brown planthopper (BPH), Nilaparvata lugens (Stål). The settling of BPH nymphs and adults was significantly less on IRGC99577, IRGC104646, and Ptb33 than on TN1. Oviposition and egg viability was less, while probing/feeding marks was more on IRGC99577 and IRGC105270 accessions. IRGC104646 showed longest trichomes while trichome density was greater in Ptb33. Largest silica cells were observed in IRGC99577 and TN1. Antixenosis resistance parameters did not show any significant association with biophysical factors. The accession IRGC99577 displayed a high level of antixenosis resistance for nymph settling, adult settling, feeding/probing marks and oviposition to BPH. This accession has emerged as a new source of resistance, which can be used for resistance breeding and to find gene/QTLs for antixenosis parameters. [ABSTRACT FROM AUTHOR]

Rice (Oryza spp.) is an important food and cash crop in the Republic of Benin. However, despite its production increase in recent years, the yield of cultivated varieties remains low, and the introduction of improved varieties threatens the rice diversity existing in traditional agriculture. Therefore, documenting the on-farm management of rice diversity, farmers' varietal preferences, and their perceptions of the performance of cultivated varieties and species are important prerequisites for the development of on-site breeding and conservation programs. To fill these gaps in Benin, 418 rice farmers, belonging to 21 ethnic groups, were surveyed in 39 villages using participatory rural appraisal tools. Subject to synonymy, 30 improved varieties and 68 local varieties were registered and their folk nomenclature and taxonomy were documented. The north of Benin had the highest diversity of rice with the greatest number of traditional varieties, making this region the best place for an in situ conservation program. The number of rice varieties maintained per village varied from 1 to 15 (six on average). The foursquare analysis revealed that the improved variety IR 841 was by far the most popular variety. Most of NERICA varieties were abandoned in the south, while the north still hosts a wide range of local varieties. Twenty-one reasons explained varietal abandonment by farmers, varying according to geographic areas and ethnic groups. The seed system was both formal and informal in the study area. The participatory evaluation revealed the necessity to create and introduce tolerant/resistant rice varieties to drought and flooding stresses in Beninese agriculture that meet farmers' preferences. Our results showed that north Benin would be the most suitable place for in situ conservation of local rice diversity. [ABSTRACT FROM AUTHOR]

Background: Zn deficiency is one of the leading public health problems in the world. Staple food crop, such as rice, cannot provide enough Zn to meet the daily dietary requirement because Zn in grain would chelate with phytic acid, which resulted in low Zn bioavailability. Breeding new rice varieties with high Zn bioavailability will be an effective, economic and sustainable strategy to alleviate human Zn deficiency. Results: The high Zn density mutant LLZ was crossed with the low phytic acid mutant Os-lpa-XS110–1, and the contents of Zn and phytic acid in the brown rice were determined for the resulting progenies grown at different sites. Among the hybrid progenies, the double mutant always displayed significantly higher Zn content and lower phytic acid content in grain, leading to the lowest molar ratio of phytic acid to Zn under all environments. As assessed by in vitro digestion/Caco-2 cell model, the double mutant contained the relatively high content of bioavailable Zn in brown rice. Conclusions: Our findings suggested pyramiding breeding by a combination of high Zn density and low phytic acid is a practical and useful approach to improve Zn bioavailability in rice grain. [ABSTRACT FROM AUTHOR]