Search

Hybrid rice (Oryza sativa) generally outperforms its inbred parents in yield and stress tolerance, a phenomenon termed heterosis, but the underlying mechanism is not completely understood. Here, we combined transcriptome, proteome, physiological, and heterosis analyses to examine the salt response of super hybrid rice Chaoyou1000 (CY1000). In addition to surpassing the mean values for its two parents (mid‐parent heterosis), CY1000 exhibited a higher reactive oxygen species scavenging ability than both its parents (over‐parent heterosis or heterobeltiosis). Nonadditive expression and allele‐specific gene expression assays showed that the glutathione S‐transferase gene OsGSTU26 and the amino acid transporter gene OsAAT30 may have major roles in heterosis for salt tolerance, acting in an overdominant fashion in CY1000. Furthermore, we identified OsWRKY72 as a common transcription factor that binds and regulates OsGSTU26 and OsAAT30. The salt‐sensitive phenotypes were associated with the OsWRKY72paternal genotype or the OsAAT30maternal genotype in core rice germplasm varieties. OsWRKY72paternal specifically repressed the expression of OsGSTU26 under salt stress, leading to salinity sensitivity, while OsWRKY72maternal specifically repressed OsAAT30, resulting in salinity tolerance. These results suggest that the OsWRKY72–OsAAT30/OsGSTU26 module may play an important role in heterosis for salt tolerance in an overdominant fashion in CY1000 hybrid rice, providing valuable clues to elucidate the mechanism of heterosis for salinity tolerance in hybrid rice. [ABSTRACT FROM AUTHOR]

Soil salinization is one of the most important abiotic stresses which can seriously affect the growth and development of rice, leading to the decrease in or even loss of a rice harvest. Increasing the rice yield of saline soil is a key issue for agricultural production. The utilization of heterosis could significantly increase crop biomass and yield, which might be an effective way to meet the demand for rice cultivation in saline soil. In this study, to elucidate the regulatory mechanisms of rice hybrids and their parents that respond to salt stress, we investigated the phenotypic characteristics, physiological and biochemical indexes, and expression level of salt-related genes at the seedling stage. In this study, two sets of materials, encapsulating the most significant differences between the rice hybrids and their parents, were screened using the salt damage index and a hybrid superiority analysis. Compared with their parents, the rice hybrids Guang-Ba-You-Hua-Zhan (BB1) and Y-Liang-You-900 (GD1) exhibited much better salt tolerance, including an increased fresh weight and higher survival rate, a better scavenging ability towards reactive oxygen species (ROS), better ionic homeostasis with lower content of Na+ in their Na+/K+ ratio, and a higher expression of salt-stress-responsive genes. These results indicated that rice hybrids developed complex regulatory mechanisms involving multiple pathways and genes to adapt to salt stress and provided a physiological basis for the utilization of heterosis for improving the yield of rice under salt stress. [ABSTRACT FROM AUTHOR]

Summary: The development of embryo sacs is crucial for seed production in plants, but the genetic basis regulating the meiotic crossover formation in the macrospore and microspore mother cells remains largely unclear. Here, we report the characterization of a spontaneous rice female sterile variation 1 mutant (fsv1) that showed severe embryo sacs abortion with low seed‐setting rate. Through map‐based cloning and functional analyses, we isolated the causal gene of fsv1, OsMLH3 encoding a MutL‐homolog 3 protein, an ortholog of HvMLH3 in barley and AtMLH3 in Arabidopsis. OsMLH3 and OsMLH1 (MutL‐homolog 1) interact to form a heterodimer (MutLγ) to promote crossover formation in the macrospore and microspore mother cells and development of functional megaspore during meiosis, defective OsMLH3 or OsMLH1 in fsv1 and CRISPR/Cas9‐based knockout lines results in reduced type I crossover and bivalent frequency. The fsv1 and OsMLH3‐knockout lines are valuable germplasms for development of female sterile restorer lines for mechanized seed production of hybrid rice. [ABSTRACT FROM AUTHOR]

Background: Benzobicyclon (BBC) is a β-triketone herbicide (bTH) used in rice paddy fields. It has the advantages of high efficiency, low toxicity, high crop safety, and good environmental compatibility, and shows efficacy against paddy weeds resistant to other types of herbicides. However, as some important indica rice varieties are susceptible to BBC, BBC is currently only registered and applied in japonica rice cultivation areas. Results: By analyzing haplotypes of the bTHs broad-spectrum resistance gene HIS1 and phenotypes for BBC in 493 major indica rice accessions in China, we identified a novel non-functional allelic variant of HIS1 in addition to the previously reported 28-bp deletion. Through detection with markers specific to the two non-functional mutations, it was clear that 25.4% of indica conventional varieties, 59.9% of fertility restorers, and 15.9% of sterile lines were susceptible to BBC. In addition, due to natural allelic variations of the HIS1 gene in the sterile and restorer lines, some two-line hybrid sterile lines were sensitive to bTHs, and the corresponding restorers were resistant. We showed the potential effectiveness of using bTHs to address the issue of two-line hybrid rice seed purity stemming from the self-crossing of sterile lines during hybrid rice seed production. Finally, allelic variations of the HIS1 gene may also play an important role in the mechanized seed production of hybrid rice. Conclusions: Our findings offer guidance for the application of BBC in indica rice areas and provide a non-transgenic approach to address the seed purity issue of two-line hybrid rice. [ABSTRACT FROM AUTHOR]

Genetic diversities or favorable genes within distantly related species are the important resources for crop genetic improvement and germplasm innovation. Spike-Stalk injection method (SSI) has long been applied in rice genetic improvement by directly introducing genetic materials from non-mating donor species, while its inheritance patterns and the underlying mechanisms are poorly elucidated. In this study, a rice variant ERV1 with improved yield-related traits was screened out in the way of introducing genomic DNA of Oryza eichingeri (2n=24, CC genome) into RH78 (Oryza sativa L. 2n=24, AA genome) using SSI method. Genome-wide comparison revealed that the genomic heterozygosity of ERV1 was approximately 8-fold higher than RH78. Restriction-site associated DNA sequencing technology (RAD-seq) and association analysis of the ERV1 inbred F2 population identified 5 quantitative trait loci (QTLs) regions responsible for these yield-related traits, and found that genomic heterozygosity of ERV1 inbred lines was significantly lower than ERV1 , while spontaneous mutation rate of the ERV1 inbred lines was significantly higher than ERV1. Our results preliminarily uncovered the inheritance patterns of SSI variant rice, and the potential genomic regions for traits changes, which yielded novel insights into the mechanisms of SSI method, and may accelerate our understanding of plant genome evolution, domestication, and speciation in nature. [ABSTRACT FROM AUTHOR]

To make better use of global germplasm resources for improving the eating quality of hybrid rice, using the resequencing data from the 3,000 rice genomes project (3K RGP), the allelic variations of the rice Wx locus were analysed. With the exception of five rare alleles discovered for the first time in our study, most of these alleles were known alleles of Wx. Furthermore, a set of Kompetitive allele-specific PCR (KASP) markers based on these Wx alleles have been developed, and thirty-six main parents of hybrid rice from 1976 to 2018 were selected for Wx genotyping. The results showed that only three Wx alleles existed in the main parents of hybrids, and the allelic combination of the hybrids changed from Wxa/Wxb and Wxlv/Wxb to Wxb/Wxb with the development of hybrid rice. Wxb is widely used in the male parents of hybrid rice. Wxa and Wxlv were used in the female parents of early hybrid rice, and they were gradually replaced by Wxb. In the future, more favourable Wx alleles from cultivated rice should be identified, introduced, and effectively used to improve hybrid rice quality. [ABSTRACT FROM AUTHOR]

The future of rice breeding will likely be built on the basis of the further utilization of heterosis between elite cultivars and genetic resources from distant subspecies of rice. Previous studies have proved that exogenous genomic DNA transformation methods can be used to transfer genetic information from distant relatives (donor) into cultivated rice (recipient). However, the mechanism underlying this form of genetic transfer is poorly characterized, and the genes that cause the phenotypic changes in these variants are typically difficult to identify. This study examined YVB, a stable variant line with greatly improved grain quality traits that was derived from an indica variety (V20B) by transferring genomic DNA of O.minuta through the 'spike-stalk injection method (SIM)'. We used restriction-site associated DNA sequencing technology (RAD-seq) to evaluate a population of BCF backcross lines (YVB × V20B); the RAD-seq data were used to construct a genetic linkage map with high-density SNPs for use in association analysis exploring genotype-phenotype relationships at the whole-genome level. A total of 17 quantitative trait loci (QTLs) for rice quality traits were mapped to chromosomes 3, 5, 6, 8, and 9. 8 major QTLs controlling different phenotypic variations were mapped to the same region of chromosome 5. This region contained the GS5 gene for grain weight and the qSW5/ GW5 gene for grain width. This study provides new resources and insights into the molecular mechanisms of grain trait phenotypic variation and the transmission of genetic information via the introduction of genomic DNA to a distantly related crop relative species. [ABSTRACT FROM AUTHOR]

• Starch fine structures contributed greatly to the eating quality of hybrid rice with similar AAC. • The starch granules of the hybrid rice with poor taste value showed greater diversity of forms and sizes. • The starch volume distribution of hybrid rice showed a bimodal-peak curve. • Hybrid rice with better taste value showed higher gelatinization enthalpy and crystallinity. In this study, we compared the physicochemical properties and starch structures of hybrid rice varieties with similar apparent amylose content but different taste values. In addition to the apparent amylose content, gel permeation chromatography analysis showed that the higher proportions of amylopectin short chains and relatively lower proportions of amylopectin long chains, which could lead to higher peak viscosity and breakdown value, as well as a softer and stickier texture of cooked rice, were the key factors in determining the eating quality of hybrid rice. High-performance anion-exchange chromatography analyses showed that the proportion of amylopectin short chains (degree of polymerization 6–10) and intermediate chains (degree of polymerization 13–24), which might affect the gelatinisation enthalpy and crystallinity, also contributed greatly to the eating quality of hybrid rice. Moreover, this study indicated that a greater diversity of forms and sizes of starch granules might influence the eating quality of hybrid rice. [ABSTRACT FROM AUTHOR]