Key Laboratory of Molecular and Cellular Biology of Ministry of Education, Hebei Collaboration Innovation Center for Cell Signaling, Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.
State Key Laboratory of Plant Cell and Chromosome Engineering, CAS Centre for Excellence in Molecular Plant, Institute of Genetics and Development Biology, Chinese Academy of Sciences, Beijing 100101, China.
Plant Cell. 2022 Sep 27;34(10):3773-3789. doi: 10.1093/plcell/koac194.
Seed size is determined by the coordinated growth of the embryo, endosperm, and integument. Growth of the integument is initiated by signal molecules released from the developing endosperm or embryo. Although recent studies have identified many components that regulate seed size by controlling integument growth, the upstream signals and the signal transduction pathway that activate these components after double fertilization are unclear. Here, we report that the receptor-like kinase ERECTA (ER) controls seed size by regulating outer integument cell proliferation in Arabidopsis thaliana. Seeds from er mutants were smaller, while those from ER-overexpressing plants were larger, than those of control plants. Different from its role in regulating the development of other organs, ER regulates seed size via a novel mechanism that is independent of its intracellular domain. Our genetic and biochemical data show that a MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) signaling pathway comprising MAPK-KINASE 4/5, MAPK 3/6 (MPK3/6), DA1, and UBIQUITIN SPECIFIC PROTEASE 15 (UBP15) functions downstream of ER and modulates seed size. MPK3/6 phosphorylation inactivates and destabilizes DA1 to increase the abundance of UBP15, promoting outer integument cell proliferation and increasing seed size. Our study illustrates a nearly completed ER-mediated signaling pathway that regulates seed size and will help uncover the mechanism that coordinates embryo, endosperm, and integument growth after double fertilization.
种子大小由胚胎、胚乳和种皮的协调生长决定。种皮的生长由发育中的胚乳或胚胎释放的信号分子启动。尽管最近的研究已经确定了许多通过控制种皮生长来调节种子大小的成分，但双受精后激活这些成分的上游信号和信号转导途径尚不清楚。在这里，我们报告说，受体样激酶 ERECTA（ER）通过调节拟南芥的外种皮细胞增殖来控制种子大小。er 突变体的种子较小，而 ER 过表达植株的种子较大，而对照植株的种子大小则处于中间水平。与 ER 在调节其他器官发育中的作用不同，ER 通过一种不依赖其细胞内结构域的新机制来调节种子大小。我们的遗传和生化数据表明，一个由丝裂原激活蛋白激酶（MAPK）组成的信号通路，包括 MAPK-激酶 4/5、MAPK3/6（MPK3/6）、DA1 和泛素特异性蛋白酶 15（UBP15），作为 ER 的下游成分，调节种子大小。MPK3/6 磷酸化使 DA1 失活和不稳定，从而增加 UBP15 的丰度，促进外种皮细胞增殖并增加种子大小。我们的研究说明了一个几乎完整的 ER 介导的信号通路，该通路调节种子大小，并将有助于揭示双受精后协调胚胎、胚乳和种皮生长的机制。
