Root nodule symbiosis (RNS) is a fascinating evolutionary event. Given that limited genes conferring the evolution of RNS in Leguminosae have been functionally validated, the genetic basis of the evolution of RNS remains largely unknown. Identifying the genes involved in the evolution of RNS will help to reveal the mystery. Here, we investigate the gene loss event during the evolution of RNS in Leguminosae through phylogenomic and synteny analyses in 48 species including 16 Leguminosae species. We reveal that loss of the Lateral suppressor gene, a member of the GRAS-domain protein family, is associated with the evolution of RNS in Leguminosae. Ectopic expression of the Lateral suppressor (Ls) gene from tomato and its homolog MONOCULM 1 (MOC1) and Os7 from rice in soybean and Medicago truncatula result in almost completely lost nodulation capability. Further investigation shows that Lateral suppressor protein, Ls, MOC1, and Os7 might function through an interaction with NODULATION SIGNALING PATHWAY 2 (NSP2) and CYCLOPS to repress the transcription of NODULE INCEPTION (NIN) to inhibit the nodulation in Leguminosae. Additionally, we find that the cathepsin H (CTSH), a conserved protein, could interact with Lateral suppressor protein, Ls, MOC1, and Os7 and affect the nodulation. This study sheds light on uncovering the genetic basis of the evolution of RNS in Leguminosae and suggests that gene loss plays an essential role.

中文翻译：

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侧抑制基因的缺失与豆科根瘤共生的进化有关


根瘤共生（RNS）是一个令人着迷的进化事件。鉴于赋予豆科 RNS 进化的有限基因已得到功能验证，RNS 进化的遗传基础在很大程度上仍然未知。鉴定参与 RNS 进化的基因将有助于揭开这个谜团。在这里，我们通过对 48 个物种（包括 16 个豆科物种）的系统发育和同线性分析，研究了豆科 RNS 进化过程中的基因丢失事件。我们发现，横向抑制基因（GRAS 结构域蛋白家族的成员）的丢失与豆科 RNS 的进化有关。番茄的侧向抑制基因 (Ls) 及其同源物 MONOCULM 1 (MOC1) 和水稻的 Os7 在大豆和蒺藜苜蓿中异位表达，导致结瘤能力几乎完全丧失。进一步研究表明，Lateral 抑制蛋白 Ls、MOC1 和 Os7 可能通过与结瘤信号通路 2 (NSP2) 和 CYCLOPS 相互作用来抑制结瘤起始 (NIN) 的转录，从而抑制豆科结瘤。此外，我们发现组织蛋白酶 H (CTSH) 作为一种保守蛋白，可以与横向抑制蛋白 Ls、MOC1 和 Os7 相互作用并影响结瘤。这项研究揭示了豆科 RNS 进化的遗传基础，并表明基因丢失起着重要作用。