Search

Fragrance is an important economic and quality trait in rice. The trait is controlled by the recessive gene betaine aldehyde dehydrogenase 2 (BADH2) via the production of 2-acetyl-1-pyrroline (2AP).Variation in BADH2 was evaluated at the population, genetic, transcriptional, and metabolic levels to obtain insights into fragrance regulation in rice.Whole-genome resequencing of the Korean World Rice Collection of 475 rice accessions, including 421 breeding lines and 54 wild accessions, was performed. Transcriptome analyses of a subset of 279 accessions, proteome analyses of 64 accessions, and volatile profiling of 421 breeding lines were also performed.We identified over 3.1 million high-quality single nucleotide polymorphisms (SNPs) in Korean rice collection. Most SNPs were present in intergenic regions (79%), and 190,148 SNPs (6%) were located in the coding sequence, of which 53% were nonsynonymous. In total, 38 haplotypes were identified in the BADH2 coding region, including four novel haplotypes (one in cultivated and three in wild accessions). Tajima's D values suggested that BADH2 was under balancing selection in japonica rice. Furthermore, we identified 316 expression quantitative trait loci (eQTL), including 185 cis-eQTLs and 131 trans-eQTLs, involved in BADH2 regulation. A protein quantitative trait loci (pQTL) analysis revealed the presence of trans-pQTLs; 13 pQTLs were mapped 1 Mbp from the BADH2 region. Based on variable importance in projection (VIP) scores, 15 volatile compounds, including 2AP, discriminated haplotypes and were potential biomarkers for rice fragrance.We generated a catalog of haplotypes based on a resequencing analysis of a large number of rice accessions. eQTLs and pQTLs associated with BADH2 gene expression and protein accumulation are likely involved in the regulation of 2AP variation in fragrant rice. These data improve our understanding of fragrance and provide valuable information for rice breeding.

Fatty acids (FAs) are important desirable compounds in oil crops. Here, we evaluated the amounts of 14 FAs in sesame grains using gas chromatography mass spectrometry and investigated the effects of genotype and environment on FA composition in 2 years. Unsaturated FA fractions accounted for 80.018% of the total FAs in sesame in 2014 and 78.936% in 2015. C16:1 and C20:1 levels exhibited few effects from the environment, while other FAs were affected significantly by environmental variance. C18:1 and C24:0 were significantly correlated with population structure. We also identified 249 QTLs that were strongly associated with the amounts of 14 FAs in sesame. These findings will be useful for understanding FA metabolism in sesame and for improving the quality of sesame through molecular breeding in the future.

Betaine aldehyde dehydrogenase 1 (BADH1), a paralog of the fragrance gene BADH2, is known to be associated with salt stress through the accumulation of synthesized glycine betaine (GB), which is involved in the response to abiotic stresses. Despite the unclear association between BADH1 and salt stress, we observed the responses of eight phenotypic characteristics (germination percentage (GP), germination energy (GE), germination index (GI), mean germination time (MGT), germination rate (GR), shoot length (SL), root length (RL), and total dry weight (TDW)) to salt stress during the germination stage of 475 rice accessions to investigate their association with BADH1 haplotypes. We found a total of 116 SNPs and 77 InDels in the whole BADH1 gene region, representing 39 haplotypes. Twenty-nine haplotypes representing 27 mutated alleles (two InDels and 25 SNPs) were highly (p &lt, 0.05) associated with salt stress, including the five SNPs that have been previously reported to be associated with salt tolerance. We observed three predominant haplotypes associated with salt tolerance, Hap_2, Hap_18, and Hap_23, which were Indica specific, indicating a comparatively high number of rice accessions among the associated haplotypes. Eight plant parameters (phenotypes) also showed clear responses to salt stress, and except for MGT (mean germination time), all were positively correlated with each other. Different signatures of domestication for BADH1 were detected in cultivated rice by identifying the highest and lowest Tajima’s D values of two major cultivated ecotypes (Temperate Japonica and Indica). Our findings on these significant associations and BADH1 evolution to plant traits can be useful for future research development related to its gene expression.

At least eight structurally related forms of vitamin E occur in nature, four tocopherols and four tocotrienols, all of which are potent membrane-soluble antioxidants. In this study, we detected two major isoforms in sesame (Sesamum indicum L.) seed: γ-tocopherol and β-tocotrienol. The objective of this study is to investigate the genetic basis of these vitamin E isoforms. We conducted a genome-wide association study (GWAS) using 5962 genome-wide markers, acquired from 96 core sesame accessions. The GWAS was performed using generalized linear (GLM) and mixed linear (MLM) models. LG08_6621957, on chromosome 8, was detected as having a significant association with γ-tocopherol in both models. It explained 20.9% of γ-tocopherol variation in sesame. For β-tocotrienol, no significant loci were detected according to the two models, but one locus, SLG03_13104062, explained 17.8% of the phenotypic variation. Based on structure and phylogenetic studies, the 96 accessions were clearly clustered into two subpopulations. This study on sesame demonstrates and provides an evidence that genotyping by sequencing (GBS) based GWAS can be used to identifying important loci for small growing crops. The significant SNPs or genes could be useful for improving the vitamin E content in sesame breeding programs.

Sesame (Sesamum indicum L.) is the queen of oil seed crops and is cultivated widely in tropical and subtropical areas. The availability of the sesame genome sequence presents unprecedented opportunities for studying its genetics, genomics, and evolution. In this report, we conducted a genome resequencing-based identification of sesame orthologs; in total, 26,379 coding sequences (CDSs) were isolated. Using a reciprocal best hit, we ultimately identified a total of 639 orthologs sets after one-to-one orthologs extraction across seven Pentapetalae plant species. These orthologs were considered to be the most credible between the two species, and in sesame. Furthermore, we performed a branch model-based maximum likelihood estimation of dN/dS of the orthologs, resulting in the identification of 198 evolutionarily accelerated orthologs and 66 positively selected genes (P-value and FDR ＜ 0.05). An enrichment analysis and protein interaction network suggested 19 genes with important functions of the orthologs specific in sesame development and domestication. The method we used here provides a case study for identifying orthologous genes between sesame and other plants species that are distributed in equilibrium phylogenetically, which can be used in other plants.

Betaine aldehyde dehydrogenase 1 (BADH1), a paralog of the fragrance gene BADH2, is known to be associated with salt stress through the accumulation of synthesized glycine betaine (GB), which is involved in the response to abiotic stresses. Despite the unclear association between BADH1 and salt stress, we observed the responses of eight phenotypic characteristics (germination percentage (GP), germination energy (GE), germination index (GI), mean germination time (MGT), germination rate (GR), shoot length (SL), root length (RL), and total dry weight (TDW)) to salt stress during the germination stage of 475 rice accessions to investigate their association with BADH1 haplotypes. We found a total of 116 SNPs and 77 InDels in the whole BADH1 gene region, representing 39 haplotypes. Twenty-nine haplotypes representing 27 mutated alleles (two InDels and 25 SNPs) were highly (p < 0.05) associated with salt stress, including the five SNPs that have been previously reported to be associated with salt tolerance. We observed three predominant haplotypes associated with salt tolerance, Hap_2, Hap_18, and Hap_23, which were Indica specific, indicating a comparatively high number of rice accessions among the associated haplotypes. Eight plant parameters (phenotypes) also showed clear responses to salt stress, and except for MGT (mean germination time), all were positively correlated with each other. Different signatures of domestication for BADH1 were detected in cultivated rice by identifying the highest and lowest Tajima’s D values of two major cultivated ecotypes (Temperate Japonica and Indica). Our findings on these significant associations and BADH1 evolution to plant traits can be useful for future research development related to its gene expression.

Background The domestication process of Asian rice (Oryza sativa L.) is complicated. It’s well established that Oryza rufipogon is the ancestor of Asian rice, although the number of domestication events still controversial. Recently, numerous types of studies based on rice nuclear genome have been conducted, but the results are quite different. Chloroplasts (cp) are also part of the rice genome and have a conserved cyclic structure that is valuable for plant genetics and evolutionary studies. Therefore, we conducted chloroplast-based studies, aiming to provide more evidence for the domestication of Asian rice. Results A total of 1389 variants were detected from the chloroplast genomes of 412 accessions obtained through the world. Oryza sativa L. ssp. japonica exhibited slightly less diversity (π) than Oryza sativa L. indica and wild rice. The fixation index values (FST) revealed that indica and japonica exhibited farther genetic distances compared with wild rice. Across cp genome, Tajima’s D test demonstrated that different selection sites occurred in Asian rice. Principal component analyses (PCA) and multidimensional scaling (MDS) clearly classify the Asian rice into different groups. Furthermore, introgression patterns identified that indica and japonica shared no introgression events in cp level, and phylogenetic studies showed cultivated rice were well separated from different type of wild rice. Conclusions Here, we focus on the domestication of Asian rice (indica and japonica). Diversity and phylogenetic analyses revealed some selection characteristics in the chloroplast genome that potentially occurred in different Asian rice during the domestication. The results shown that Asian rice had been domesticated at least twice. In additional, japonica may experience a strong positive selection or bottleneck event during the domestication. Electronic supplementary material The online version of this article (10.1186/s12284-019-0322-x) contains supplementary material, which is available to authorized users.

Figure S2. The joint number distribution of allele frequencies in japonica and indica. (a). The joint number of indica and temperate japonica based on their allele frequencies. (b). The joint number of indica and tropical japonica based on their allele frequencies. (c). The frequency of site of indica and temperate japonica for introgression event. (d) . The frequency of site of indica and tropical japonica for introgression event. Here, we marked the site (yellow) of frequency bigger than 95% or small than 5%. (PDF 483 kb)