Department of Genetics and Biochemistry, Clemson University, Clemson, SC, 29630-0318, USA.
Plant J. 2016 Oct;88(1):108-119. doi: 10.1111/tpj.13234. Epub 2016 Aug 21.
Autoregulation of nodulation (AON), a systemic signaling pathway in legumes, limits the number of nodules formed by the legume in its symbiosis with rhizobia. Recent research suggests a model for the systemic regulation in Medicago truncatula in which root signaling peptides are translocated to the shoot where they bind to a shoot receptor complex containing the leucine-rich repeat receptor-like kinase SUNN, triggering signal transduction which terminates nodule formation in roots. Here we show that a tagged SUNN protein capable of rescuing the sunn-4 phenotype is localized to the plasma membrane and is associated with the plasmodesmata. Using bimolecular fluorescence complementation analysis we show that, like its sequence ortholog Arabidopsis CLV1, SUNN interacts with homologous CLV1-interacting proteins MtCLAVATA2 and MtCORYNE. All three proteins were also able to form homomers and MtCRN and MtCLV2 also interact with each other. A crn Tnt1 insertion mutant of M. truncatula displayed a shoot controlled increased nodulation phenotype, similar to the clv2 mutants of pea and Lotus japonicus. Together these data suggest that legume AON signaling could occur through a multi-protein complex and that both MtCRN and MtCLV2 may play roles in AON together with SUNN.
共生结瘤的自身调控（AON）是豆科植物中的一种系统信号通路，它限制了豆科植物与其根瘤菌共生时形成根瘤的数量。最近的研究提出了一个关于蒺藜苜蓿系统调控的模型，其中根信号肽被转运到地上部分，在那里它们与含有富含亮氨酸重复的受体样激酶 SUNN 的地上受体复合物结合，触发信号转导，从而终止根部的根瘤形成。在这里，我们表明能够拯救 sunn-4 表型的标记 SUNN 蛋白定位于质膜，并与胞间连丝相关。使用双分子荧光互补分析，我们表明，SUNN 与其序列同源物拟南芥 CLV1 一样，与同源的 CLV1 相互作用蛋白 MtCLAVATA2 和 MtCORYNE 相互作用。这三种蛋白都能够形成同源二聚体，MtCRN 和 MtCLV2 也相互作用。蒺藜苜蓿的 crn Tnt1 插入突变体表现出地上部分控制的过度结瘤表型，类似于豌豆和百脉根的 clv2 突变体。这些数据表明，豆科植物 AON 信号可能通过多蛋白复合物发生，MtCRN 和 MtCLV2 可能与 SUNN 一起在 AON 中发挥作用。
