National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Shanghai 200032, China; University of the Chinese Academy of Sciences, Beijing 100049, China.
National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Shanghai 200032, China.
Mol Plant. 2022 Mar 7;15(3):468-487. doi: 10.1016/j.molp.2021.11.013. Epub 2021 Nov 27.
Maize (Zea mays) endosperm filling is coordinated with cell expansion to enlarge the grain size, but the mechanism coupling the two processes is poorly understood. Starchy endosperm cells basically contain no visible vacuoles for cell expansion. During grain filling, efficient synthesis of storage compounds leads to reduced cytoplasm and thus lowered cell turgor pressure. Although bioactive gibberellins (GAs) are essential for cell expansion, they accumulate at a low level at this stage. In this study, we identified an endosperm-specific GRAS domain-containing protein (ZmGRAS11) that lacks the DELLA domain and promotes cell expansion in the filling endosperm. The zmgras11 loss-of-function mutants showed normal grain filling but delayed cell expansion, thereby resulting in reduced kernel size and weight. Overexpression of ZmGRAS11 led to larger endosperm cells and therefore increased kernel size and weight. Consistent with this, ZmGRAS11 positively regulates the expression of ZmEXPB12, which is essential for cell expansion, at the endosperm filling stage. Moreover, we found that Opaque2 (O2), a central transcription factor that regulates endosperm filling, could directly bind to the promoter of ZmGRAS11 and activate its expression. Taken together, these results suggest that endosperm cell expansion is coupled with endosperm filling, which is orchestrated by the O2-ZmGRAS11-centered transcriptional regulatory network. Our findings also provide potential targets for maize yield improvement by increasing the storage capacity of endosperm cells.
玉米（Zea mays）胚乳填充与细胞扩展相协调，以增大籽粒大小，但这两个过程的耦联机制尚不清楚。淀粉胚乳细胞基本上不含可见的液泡用于细胞扩展。在灌浆期间，有效合成储存化合物会导致细胞质减少，从而降低细胞膨压。尽管生物活性赤霉素（GAs）对于细胞扩展是必需的，但在这个阶段它们的积累水平较低。在本研究中，我们鉴定了一个胚乳特异性 GRAS 结构域蛋白（ZmGRAS11），它缺乏 DELLA 结构域，并促进填充胚乳中的细胞扩展。Zmgras11 功能丧失突变体表现出正常的灌浆，但细胞扩展延迟，从而导致籽粒大小和重量减小。ZmGRAS11 的过表达导致胚乳细胞更大，从而增加了籽粒大小和重量。与此一致的是，ZmGRAS11 正向调节ZmEXPB12 的表达，ZmEXPB12 对于细胞扩展是必需的，在胚乳填充阶段。此外，我们发现，调控胚乳填充的中心转录因子 Opaque2 (O2) 可以直接结合ZmGRAS11 的启动子并激活其表达。总之，这些结果表明，胚乳细胞扩展与胚乳填充相耦联，由 O2-ZmGRAS11 为中心的转录调控网络协调。我们的发现还为通过增加胚乳细胞的储存能力来提高玉米产量提供了潜在的目标。
