Grain weight is a major determinant of grain yield. GS5 is a positive regulator of grain size such that grain width, filling, and weight are correlated with its expression level. Previous work suggested that polymorphisms of GS5 in the promoter region might be responsible for the variation in grain size. In this study, two single nucleotide polymorphisms (SNPs) between the wide-grain allele GS5-1 and the narrow-grain allele GS5-2 in the upstream region of the gene that were responsible for the differential expression in developing young panicles were identified. These two polymorphs altered the responses of the GS5 alleles to abscisic acid (ABA) treatments, resulting in higher expression of GS5-1 than of GS5-2 in developing young panicles. It was also shown that SNPs in light-responsive elements of the promoter altered the response to light induction, leading to higher expression of GS5-2 than GS5-1 in leaves. Enhanced expression of GS5 competitively inhibits the interaction between OsBAK1-7 and OsMSBP1 by occupying the extracellular leucine-rich repeat (LRR) domain of OsBAK1-7, thus preventing OsBAK1-7 from endocytosis caused by interacting with OsMSBP1, providing an explanation for the positive association between grain size and GS5 expression. These results advanced our understanding of the molecular mechanism by which GS5 controls grain size.
粒重是影響籽粒產(chǎn)量的一個主要決定因素。GS5是籽粒大小的正向調(diào)控因子，如粒寬、灌漿以及重量等均與其表達水平有關(guān)。之前研究表明GS5啟動子區(qū)域的多態(tài)性可能決定籽粒大小的差異。本文對寬粒等位基因GS5-1和窄粒等位基因GS5-2上游區(qū)域的兩個單核苷酸多態(tài)性（SNPs）進行了鑒定，它們影響發(fā)育幼穗中GS5的表達變化。這兩個多態(tài)性改變了GS5等位基因?qū)γ撀渌幔ˋBA）處理的應(yīng)答，并導(dǎo)致發(fā)育幼穗中GS5-1的表達量高于GS5-2。同時啟動子區(qū)域光響應(yīng)元件中的SNPs改變了對光誘導(dǎo)的應(yīng)答，導(dǎo)致葉片中GS5-2表達量高于GS5-1。GS5表達增強會通過占據(jù)OsBAK1-7的胞外富亮氨酸重復(fù)（LRR）結(jié)構(gòu)域，競爭性地抑制OsBAK1-7和OsMSBP1間的互作，進而阻止OsBAK1-7通過與OsMSBP1互作而產(chǎn)生的胞吞作用，為籽粒大小和GS5表達間的正相關(guān)作用提供了一個很好的解釋。這些結(jié)果加深了我們對GS5控制籽粒大小分子機理的理解。