Background: Low temperature is a limiting factor of rice productivity and geographical distribution. Wild rice (Oryza rufipogon Griff.) is an important germplasm resource for rice improvement. It has superior tolerance to many abiotic stresses, including cold stress, but little is known about the mechanism underlying its resistance to cold. Results: This study elucidated the molecular genetic mechanisms of wild rice in tolerating low temperature. Comprehensive transcriptome profiles of two rice genotypes (cold-sensitive ce 253 and cold-tolerant Y12-4) at the germinating stage under cold stress were comparatively analyzed. A total of 42.44-68.71 million readings were obtained, resulting in the alignment of 29,128 and 30,131 genes in genotypes 253 and Y12-4, respectively. Many common and differentially expressed genes (DEGs) were analyzed in the cold-sensitive and cold-tolerant genotypes. Results showed more upregulated DEGs in the cold-tolerant genotype than in the cold-sensitive genotype at four stages under cold stress. Gene ontology enrichment analyses based on cellular process, metabolic process, response stimulus, membrane part, and catalytic activity indicated more upregulated genes than downregulated ones in the cold-tolerant genotype than in the cold-sensitive genotype. Quantitative real-time polymerase chain reaction was performed on seven randomly selected DEGs to confirm the RNA Sequencing (RNA-seq) data. These genes showed similar expression patterns corresponding with the RNA-Seq method. Weighted gene co-expression network analysis (WGCNA) revealed Y12-4 showed more positive genes than 253 under cold stress. We also explored the cold tolerance gene LTG5 (Low Temperature Growth 5) encoding a UDP-glucosyltransferase. The overexpression of the LTG5 gene conferred cold tolerance to indica rice. Conclusion: Gene resources related to cold stress from wild rice can be valuable for improving the cold tolerance of crops.
The anthocyanin biosynthesis of rice is a major concern due to the potential nutritional value. Purple appears in various organs and tissues of rice such as pericarp, flower organs, leaves, leaf sheaths, internodes, ligules, apex, and stigma. At present, there are many studies on the color of rice pericarp, but the gene and mechanism of other organs such as leaves are still unclear, and the gene regulatory network of specific organ coloring has not been systematically understood. In this study, genetic analysis demonstrated that the purple leaf traits of rice were regulated by a recessive gene. The green leaf cultivar Y58S and purple leaf cultivar XianHongB were used to construct the mapping population. A set of near isogenicline (NIL) (BC3F1) was bred via crossing and back-crossing. The generations of BC3F2 appeared to separate four phenotypes, pl1, pl2, pl3, and pl4, due to the occurrence of a purple color in different organs. We constructed three bulked segregant analysis (BSA) pools (pl1–pl2, pl1–pl3, and pl1–pl4) by using the separated generations of BC3F5 and mapped the purple leaf gene plr4 to the vicinity of 27.9–31.1 Mb on chromosome 4. Subsequently, transcriptome sequencing (RNA-Seq) for pl3 and pl2 was used to analyze the differentially expressed genes in the localization interval, where 12 unigenes exhibited differential expression in which two genes (Os04g0577800, Os04g0616400) were downregulated. The two downregulated genes (Os04g0577800 and Os04g0616400) are possible candidate genes because of the recessive genetic characteristics of the purple leaf genes. These results will facilitate the cloning of plr4 and illustrate the molecular mechanisms of the anthocyanin synthesis pathway.
Rice (Oryza sativa L.) is an important staple food crop for more than half of the world’s population. Enhancing the grain quality and yield of rice to meet growing demand remains a major challenge. Here, we show that OsMKK3 encode a MAP kinase kinase that controls grain size and chalkiness by affecting cell proliferation in spikelet hulls. We showed that OsSPL16, GS5, and GIF1 have a substantial effect on the OsMKK3-regulated grain size pathway. OsMKK3 has experienced strong directional selection in indica and japonica. Wild rice accessions contained four OsMKK3 haplotypes, suggesting that the OsMKK3 haplotypes present in cultivated rice likely originated from different wild rice accessions during rice domestication. OsMKK3-Hap1, gs3, and gw8 were polymerized to enhance the grain length. Polymerization of beneficial alleles, such as OsMKK3-Hap1, gs3, gw8, fgr, alk, chalk5, and wx, also improved the quality of hybrid rice. Overall, the results indicated that beneficial OsMKK3 alleles could be used for genomic-assisted breeding for rice cultivar improvement and be polymerized with other beneficial alleles.
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