Yuan Hua, Fan Shijun, Huang Juan, Zhan Shijie, Wang Shifu, Gao Peng, Chen Weilan, Tu Bin, Ma Bingtian, Wang Yuping, Qin Peng, Li Shigui
Rice Research Institute of Sichuan Agricultural University, Chengdu Wenjiang, Sichuan, 611130, China.
State Key Laboratory of Hybrid Rice, Sichuan Agricultural University, Chengdu Wenjiang, Sichuan, 611130, China.
Rice (N Y). 2017 Dec;10(1):25. doi: 10.1186/s12284-017-0165-2. Epub 2017 May 25.
Both grain size and grain number are significant for rice yield. In the past decade, a number of genes related to grain size and grain number have been documented, however, the regulatory mechanisms underlying them remains ambiguous.
We identified a rice small grain (sg2) mutant in an EMS mutant library generated from an indica variety, Shuhui498. Using the MutMap gene mapping strategy, we identified two linkage regions on chromosome 7 and 8, respectively, consistent with the segregation ratios in the F population. We focused on the linkage region on chromosome 8, and named this locus as 08sg2. One of three SNPs identified in the linkage region was located in an exon of OsBAK1, leading to a nonsynonymous mutation in the kinase domain. The plant harboring the mutant version 08sg2 locus exhibited a decreased grain size, grain number and plant height. Cytological analysis indicated that 08SG2 regulated spikelet hull development by affecting cell proliferation. The grain size and number of knockout mutants of OsBAK1 in the japonica background were significantly decreased, but less so than in 08sg2, supporting the idea that the SNP in OsBAK1 was responsible for the 08sg2 phenotype, but that 08SG2/OsBAK1 function differently in indica and japonica backgrounds. 08sg2 was insensitive to 24-epiBL, and the expression of BR-related genes was obviously altered in 08sg2. The proportionally decreased grain length when 08sg2 and GS3 were combined indicate that 08SG2 and GS3 regulate grain length independently.
Our work shows that 08SG2/OsBAK1 is important for rice yield in both indica and japonica backgrounds, by regulating grain size and grain number, and the function of 08SG2/OsBAK1 is obviously affected by genetic background. The amino acid substituted in 08sg2 is highly conserved among different species, supporting the idea that it is important for the molecular function of 08SG2/OsBAK1. Together, our work is helpful for fully understanding the function of 08SG2/OsBAK1.
籽粒大小和粒数对水稻产量都很重要。在过去十年中，已经报道了许多与籽粒大小和粒数相关的基因，然而，其潜在的调控机制仍不明确。
我们在由籼稻品种蜀恢498构建的EMS突变体库中鉴定出一个水稻小粒（sg2）突变体。使用MutMap基因定位策略，我们分别在第7和第8号染色体上鉴定出两个连锁区域，这与F群体中的分离比例一致。我们聚焦于第8号染色体上的连锁区域，并将该位点命名为08sg2。在连锁区域鉴定出的三个单核苷酸多态性（SNP）之一位于OsBAK1的一个外显子中，导致激酶结构域发生非同义突变。携带突变型08sg2位点的植株籽粒大小、粒数和株高均降低。细胞学分析表明，08SG2通过影响细胞增殖来调控小穗颖壳发育。粳稻背景下OsBAK1基因敲除突变体的籽粒大小和粒数显著降低，但低于08sg2，这支持了OsBAK1中的SNP导致08sg2表型的观点，但08SG2/OsBAK1在籼稻和粳稻背景中的功能不同。08sg2对24-表油菜素内酯（24-epiBL）不敏感，且08sg2中油菜素内酯（BR）相关基因的表达明显改变。08sg2与GS3组合时籽粒长度成比例降低，表明08SG2和GS3独立调控籽粒长度。
我们的研究表明，08SG2/OsBAK1通过调控籽粒大小和粒数，对籼稻和粳稻背景下的水稻产量都很重要，且08SG2/OsBAK1的功能明显受遗传背景影响。08sg2中取代的氨基酸在不同物种间高度保守，这支持了其对08SG2/OsBAK1分子功能很重要的观点。总之，我们的研究有助于全面了解08SG2/OsBAK1的功能。
