Rice ( Oryza sativa L.) is one of the most important food crops, and its yield is mainly determined by the number of effective tillers, grains per panicle and grain weight. Grain shape is positively correlated with grain weight, which is the key factor determining rice yield, so grain shape has always been an important target trait in rice breeding. In recent years, a number of key genes involved in grain shape regulation in rice have been reported, and these genes are involved in a variety of signaling pathways. Auxin plays an important regulatory role in all stages of plant growth and development. Scientists have cloned a series of star genes that control rice grain shape, but the molecular mechanism by which auxin regulates rice grain shape is still unclear.
Recently, a research article entitled "The OsbHLH166- OsABCB4 module regulates grain length and weight via altering auxin efflux" was published online in Science Bulletin, which was reported by first author, Lina Du in Inner Mongolia University and co-corresponding with Professor Yanhua Qi of Inner Mongolia University, Academician Qian Qian of Yazhouwan National Laboratory and researcher Zhenyu Gao of China National Rice Research Institute. This study reported the biological function of the OsbHLH166- OsABCB4 module in regulating rice grain shape. The research results not only reveal the genetic regulation mechanism of rice grain shape from a new perspective, but also provide new genetic resources for high-yield rice breeding.
This study detected the quantitative trait locus qGL1 related to grain length in the recombinant inbred line populations of 9311 and Nipponbare (NIP), and fine-mapped it to the OsABCB4 gene that encodes a member of the ATP-binding cassette B (ABCB) subfamily. Compared with NIP, the OsABCB4 gene mutation resulted in longer and heavier grains, while overexpression resulted in shorter and lighter grains, suggesting that OsABCB4 negatively regulates rice grain length and weight. OsbHLH166, a basic helix-loop-helix transcription factor, was screened from yeast one-hybrid library. Electrophoretic mobility shift assay and yeast one hybridization validation confirmed that the transcription factor directly binds to the promoter region of OsABCB4 , and it was further confirmed that it promotes the expression of OsABCB4 by dual-luciferase reporter assay. OsABCB4 encodes auxin efflux transporter localized to plasma membrane, histological analysis, IAA content measurement and DR5:GUS activity showed that OsbHLH166 and OsABCB4 regulated grain length and weight by regulating cell expansion and auxin content in glume cells, as well as changing the expression of GL7 , GS2 , TGW3 and GS3 genes during grain development. This study revealed a new molecular regulatory mechanism that regulates grain length and weight, and provided new targets and transformation strategies for molecular breeding of efficient rice yield improvement.
Science Bulletin