籽粒大小是水稻产量的重要决定因素之一。我们以前的研究表明,乙烯在粒度控制中起着重要作用;然而,确切的机制还有待确定。这里,我们报告说,乙烯响应因子OsERF115是乙烯介导的谷物发育的关键下游调节剂。OsERF115编码AP2/ERF型转录因子,该转录因子在幼小小穗和发育中的圆锥体中特异性表达。OsERF115的过表达显著增加了晶粒长度,宽度,通过促进小穗壳细胞的纵向伸长和横向分裂,以及增强谷物灌浆活动,而它的敲除突变会导致相反的效果,表明OsERF115正向调节晶粒尺寸和重量。OsERF115转录受到乙烯的强烈诱导,和OsEIL1直接与启动子结合以激活其表达。OsERF115作为转录抑制因子,在小穗生长和胚乳发育过程中直接或间接调节一组粒级基因。重要的是,单倍型分析显示,OsERF115启动子的EIN3结合位点的SNP变异与OsERF115表达水平和粒重显著相关,表明OsERF115启动子的自然变异有助于颗粒大小的多样性。此外,OsERF115直系同源物仅在草种中被鉴定,暗示在谷物作物的谷物发育中具有保守而独特的作用。我们的结果为乙烯介导的粒级控制的分子机制和基于OsEIL1-OsERF115靶基因调控模块的水稻产量遗传改良提供了见解。
Grain size is one of the essential determinants of rice yield. Our previous studies revealed that ethylene plays an important role in grain-size control; however, the precise mechanism remains to be determined. Here, we report that the ethylene response factor OsERF115 functions as a key downstream regulator for ethylene-mediated grain development. OsERF115 encodes an AP2/ERF-type transcriptional factor that is specifically expressed in young spikelets and developing caryopses. Overexpression of OsERF115 significantly increases grain length, width, thickness and weight by promoting longitudinal elongation and transverse division of spikelet hull cells, as well as enhancing grain-filling activity, whereas its knockout mutations lead to the opposite effects, suggesting that OsERF115 positively regulates grain size and weight. OsERF115 transcription is strongly induced by ethylene, and OsEIL1 directly binds to the promoter to activate its expression. OsERF115 acts as a transcriptional repressor to directly or indirectly modulate a set of grain-size genes during spikelet growth and endosperm development. Importantly, haplotype analysis reveals that the SNP variations in the EIN3-binding sites of OsERF115 promoter are significantly associated with the OsERF115 expression levels and grain weight, suggesting that natural variations in the OsERF115 promoter contribute to grain-size diversity. In addition, the OsERF115 orthologues are identified only in grass species, implying a conserved and unique role in the grain development of cereal crops. Our results provide insights into the molecular mechanism of ethylene-mediated grain-size control and a potential strategy based on the OsEIL1-OsERF115-target gene regulatory module for genetic improvement of rice yield.