Background: The heterotrimeric G protein complex, consisting of Gα, Gβ, and Gγ subunits, are conserved signal transduction mechanism in eukaryotes. Recent molecular researches had demonstrated that G protein signaling participates in the regulation of yield related traits. However, the effects of G protein genes on yield components and stress tolerance are not well characterized. Results: In this study, we generated heterotrimeric G protein mutants in rice using CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) gene-editing technology. The effects of heterotrimeric G proteins on the regulation of yield components and stress tolerance were investigated. The mutants of gs3 and dep1 generated preferable agronomic traits compared to the wild-type, whereas the mutants of rga1 showed an extreme dwarf phenotype, which led to a dramatic decrease in grain production. The mutants showed improved stress tolerance, especially under salinity treatment. We found four putative extra-large G proteins (PXLG)1–4 that also participate in the regulation of yield components and stress tolerance. A yeast two hybrid showed that the RGB1 might interact with PXLG2 but not with PXLG1, PXLG3 or PXLG4. Conclusion: These findings will not only improve our understanding of the repertoire of heterotrimeric G proteins in rice but also contribute to the application of heterotrimeric G proteins in rice breeding.

Two of the most widely cultivated rice strains are Oryza sativa indica and O. sativa japonica, and understanding the genetic basis of their agronomic traits is of importance for crop production. These two species are highly distinct in terms of geographical distribution and morphological traits. However, the relationship among genetic background, ecological conditions, and agronomic traits is unclear. In this study, we performed the de novo assembly of a high-quality genome of SN265, a cultivar that is extensively cultivated as a backbone japonica parent in northern China, using single-molecule sequencing. Recombinant inbred lines (RILs) derived from a cross between SN265 and R99 (indica) were re-sequenced and cultivated in three distinct ecological conditions. We identify 79 QTLs related to 15 agronomic traits. We found that several genes underwent functional alterations when the ecological conditions were changed, and some alleles exhibited contracted responses to different genetic backgrounds. We validated the involvement of one candidate gene, DEP1, in determining panicle length, using CRISPR/Cas9 gene editing. This study provides information on the suitable environmental conditions, and genetic background, for functional genes in rice breeding. Moreover, the public availability of the reference genome of northern japonica SN265 provides a valuable resource for plant biologists and the genetic improvement of crops.

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The DEP1 (dense and erect panicle 1) gene, which corresponds to the erect panicle architecture, shows a pleiotropic effect in increasing grain yield and nitrogen use efficiency (NUE) in rice. Nevertheless, it remains unclear whether the carbon−nitrogen metabolic balance changes as the dep1 allele enhances nitrogen uptake and assimilation. In this study, we generated transgenic Akitakomati plants by overexpressing dep1 and analyzed the carbon−nitrogen metabolic status, gene expression profiles, and grain yield and quality. Under either low or high nitrogen growth conditions, the carbon−nitrogen metabolic balance of dep1-overexpressed lines was broken in stem sheaths and leaves but not in grains; the dep1-overexpressed plants showed higher expressions of glutamine synthetase (GS) and glutamate synthase (GOGAT) genes than the wildtype, along with increased total nitrogen and soluble protein content in the straw at maturity. However, the ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) and phosphoenolpyruvate carboxylase (PEPC) genes were downregulated in dep1-overexpressed plants, leading to a decreased carbohydrate content and carbon/nitrogen ratio. Although the unbalanced carbon−nitrogen metabolism decreased the grain-filling rate, grain setting percentage, 1000 grain weight, and grain quality in dep1-overexpressed lines, it led to increased grain numbers per panicle and consequently increased grain yield. Our results suggest that an unbalanced carbon−nitrogen metabolic status is a major limiting factor for further improving grain yield and quality in erect panicle varieties.