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.

中文翻译：

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OsEIL1-OsERF115-靶基因调控模块控制水稻粒大小和重量

籽粒大小是水稻产量的重要决定因素之一。我们之前的研究表明，乙烯在粒度控制中起着重要作用。然而，确切的机制仍有待确定。在这里，我们报告乙烯反应因子 OsERF115 是乙烯介导的谷物发育的关键下游调节因子。OsERF115编码一种 AP2/ERF 型转录因子，该因子在幼小小穗和发育中的颖果中特异性表达。OsERF115的过表达通过促进小穗壳细胞的纵向伸长和横向分裂以及增强灌浆活性显着增加籽粒长度、宽度、厚度和重量，而其敲除突变导致相反的效果，表明OsERF115正向调节谷物大小和重量。OsERF115转录受乙烯强烈诱导，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晶粒大小的基因。重要的是，单倍型分析表明，OsERF115启动子的 EIN3 结合位点的 SNP 变异与OsERF115表达水平和粒重显着相关，表明OsERF115启动子的自然变异有助于粒大小的多样性。此外，OsERF115直系同源物仅在草种中被发现，这意味着在谷类作物的谷物发育中具有保守和独特的作用。我们的研究结果为乙烯介导的粒度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的潜在策略提供了见解。