Grain number per-panicle is one of the most important components for rice yield. Spikelets on the primary and secondary branches determine the grain number per-panicle in rice. In this study, we identified a natural mutant, gnp4, lack of lateral spikelet on the secondary branches in the field condition. In addition, the Gnp4 and Lax1-1 double mutant showed dramatically reduced secondary branches and spikelets in panicle at reproductive stage, and tillers at vegetative stage. By map-based cloning approach, and using four F2 segregating populations, the Gnp4 gene was finally mapped to a 10.7-kb region on the long arm of chromosome 4 in rice. In this region, only one gene was predicted, and genomic DNA sequencing of the 10.7-kb region showed no nucleotide differences between the mutant and wild type. Interestingly, we found that the methylation level of several cytosines in the promoter CpG islands region of the predicted gene in gnp4 were different from the wild type. Thus, we propose that the DNA methylation changes at these sites may induce to decrease expression level of Gnp4, consequently, resulting in phenotypic variation.
每穗粒數(shù)是構(gòu)成水稻產(chǎn)量最重要的因子之一。一次枝梗和二次枝梗上的小穗數(shù)決定了每穗粒數(shù)。本研究，我們鑒定到一個(gè)來(lái)自田間的自然突變體，gnp4，其二次枝梗上不著生小穗。此外，Gnp4 Lax1-1雙突變體，在生殖生長(zhǎng)期二次枝梗和小穗顯著減少，在營(yíng)養(yǎng)生長(zhǎng)期分蘗顯著減少。利用4個(gè)F2分離群體，通過圖位克隆，將Gnp4精細(xì)定位在水稻4號(hào)染色體長(zhǎng)臂一個(gè)10.7kb的區(qū)間內(nèi)。在該區(qū)間內(nèi)，只有一個(gè)候選基因，并對(duì)這10.7kb的基因組DNA進(jìn)行了測(cè)序，在突變體和野生型之間，沒有發(fā)現(xiàn)堿基差異。有趣的是，我們發(fā)現(xiàn)在gnp4預(yù)測(cè)基因啟動(dòng)子的CpG島區(qū)域，胞嘧啶的甲基化水平，突變體和野生型存在差異。所以，我們認(rèn)為該位點(diǎn)的DNA甲基化，可能是引起Gnp4基因表達(dá)水平下降，以及導(dǎo)致表型變異的原因。