NCP1/AtMOB1A Plays Key Roles in Auxin-Mediated <i>Arabidopsis</i> Development

MOB1 protein is a core component of the Hippo signaling pathway in animals where it is involved in controlling tissue growth and tumor suppression. Plant MOB1 proteins display high sequence homology to animal MOB1 proteins, but little is known regarding their role in plant growth and development. Herein we report the critical roles of Arabidopsis MOB1 (AtMOB1A) in auxin-mediated development in Arabidopsis. We found that loss-of-function mutations in AtMOB1A completely eliminated the formation of cotyledons when combined with mutations in PINOID (PID), which encodes a Ser/Thr protein kinase that participates in auxin signaling and transport. We showed that atmob1a was fully rescued by its Drosophila counterpart, suggesting functional conservation. The atmob1a pid double mutants phenocopied several well-characterized mutant combinations that are defective in auxin biosynthesis or transport. Moreover, we demonstrated that atmob1a greatly enhanced several other known auxin mutants, suggesting that AtMOB1A plays a key role in auxin-mediated plant development. The atmob1a single mutant displayed defects in early embryogenesis and had shorter root and smaller flowers than wild type plants. AtMOB1A is uniformly expressed in embryos and suspensor cells during embryogenesis, consistent with its role in embryo development. AtMOB1A protein is localized to nucleus, cytoplasm, and associated to plasma membrane, suggesting that it plays roles in these subcellular localizations. Furthermore, we showed that disruption of AtMOB1A led to a reduced sensitivity to exogenous auxin. Our results demonstrated that AtMOB1A plays an important role in Arabidopsis development by promoting auxin signaling.MOB1蛋白（MOB1 protein）是动物体内Hippo信号通路（Hippo signaling pathway）的核心组分，参与调控组织生长与肿瘤抑制。植物MOB1蛋白与动物MOB1蛋白序列同源性极高，但目前对其在植物生长发育中的功能尚不清楚。本研究报道了拟南芥（Arabidopsis）MOB1蛋白（AtMOB1A）在生长素（auxin）介导的拟南芥发育过程中的关键作用。我们发现，当AtMOB1A功能缺失突变体与编码丝氨酸/苏氨酸蛋白激酶（Ser/Thr protein kinase）的PINOID（PID）发生突变时，双突变体完全无法形成子叶，其中PINOID（PID）所编码的丝氨酸/苏氨酸蛋白激酶参与生长素信号转导与运输过程。我们证实，果蝇（Drosophila）来源的AtMOB1A同源蛋白可完全互补atmob1a突变体，提示其功能保守性。atmob1a pid双突变体的表型与数个已被充分表征的生长素生物合成或运输缺陷突变组合一致。此外，我们发现atmob1a显著增强了其他已知生长素相关突变体的表型，表明AtMOB1A在生长素介导的植物发育中发挥关键作用。atmob1a单突变体在早期胚胎发生过程中存在发育缺陷，且相较于野生型植株，其根系更短、花朵更小。AtMOB1A在胚胎发生过程中的胚与胚柄细胞中均一表达，这与其在胚胎发育中的功能相符。AtMOB1A蛋白定位于细胞核、细胞质，并与质膜（plasma membrane）相关联，提示其在这些亚细胞区域发挥功能。进一步研究发现，AtMOB1A的功能缺失会导致植株对外源生长素的敏感性降低。本研究结果证实，AtMOB1A通过促进生长素信号转导，在拟南芥发育过程中发挥重要作用。