Legume plants form a symbiosis with N2-fixing soil rhizobia, resulting in new root organs called nodules that enable N2-fixation. Nodulation is a costly process that is tightly regulated by the host through Autoregulation of Nodulation (AON) and nitrate-dependent regulation of nodulation. Both pathways require legume-specific CLAVATA/ESR-related (CLE) peptides. Nitrogen-induced nodulation-suppressing CLE peptides have not previously been characterised in Medicago truncatula, with only rhizobia-induced MtCLE12 and MtCLE13 identified. Here, we report on novel peptides MtCLE34 and MtCLE35 in nodulation control pathways. The nodulation-suppressing CLE peptides of five legume species were classified into three clades based on sequence homology and phylogeny. This approached identified MtCLE34 and MtCLE35 and four new CLE peptide orthologues of Pisum sativum. Whereas MtCLE12 and MtCLE13 are induced by rhizobia, MtCLE34 and MtCLE35 respond to both rhizobia and nitrate. MtCLE34 was identified as a pseudogene lacking a functional CLE-domain. Overexpression of MtCLE12, MtCLE13 and MtCLE35 inhibits nodulation. Together, our findings indicate that MtCLE12 and MtCLE13 have a distinct role in AON, while MtCLE35 regulates nodule numbers in a rhizobia- and nitrate-dependent manner. MtCLE34 likely had a similar role to MtCLE35 but its function was lost due to a nonsense mutation resulting in the loss of the mature peptide.

中文翻译：

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结节控制中t藜苜蓿CLE34和CLE35的表征

豆科植物与固氮的土壤根瘤菌共生，产生了新的根瘤，称为根瘤，能够固氮。结瘤是一个昂贵的过程，宿主通过结瘤的自动调节（AON）和硝酸盐依赖性的结瘤调节对其进行严格调节。两种途径都需要豆科植物特异性的CLAVATA / ESR相关（CLE）肽。之前在in藜苜蓿中尚未鉴定出氮诱导的抑制结瘤的CLE肽，仅鉴定了根瘤菌诱导的MtCLE12和MtCLE13。在这里，我们报告结瘤控制途径中的新型肽MtCLE34和MtCLE35。根据序列同源性和系统发育，将五个豆科植物抑制结节的CLE肽分为三个进化枝。该方法可鉴定出豌豆（Pisum sativum）的MtCLE34和MtCLE35以及四个新的CLE肽直向同源物。MtCLE12和MtCLE13是由根瘤菌诱导的，而MtCLE34和MtCLE35对根瘤菌和硝酸盐都有反应。MtCLE34被鉴定为缺乏功能性CLE域的假基因。MtCLE12，MtCLE13和MtCLE35的过表达抑制结瘤。总之，我们的发现表明MtCLE12和MtCLE13在AON中具有独特的作用，而MtCLE35以根瘤菌和硝酸盐依赖性的方式调节结节数。MtCLE34可能具有与MtCLE35类似的作用，但由于无义突变而导致其功能丧失，导致成熟肽的丧失。MtCLE12，MtCLE13和MtCLE35的过表达抑制结瘤。总之，我们的发现表明MtCLE12和MtCLE13在AON中具有独特的作用，而MtCLE35以根瘤菌和硝酸盐依赖性的方式调节结节数。MtCLE34可能具有与MtCLE35类似的作用，但由于无义突变而导致其功能丧失，导致成熟肽的丧失。MtCLE12，MtCLE13和MtCLE35的过表达抑制结瘤。总之，我们的发现表明MtCLE12和MtCLE13在AON中具有独特的作用，而MtCLE35以根瘤菌和硝酸盐依赖性的方式调节结节数。MtCLE34可能具有与MtCLE35类似的作用，但由于无义突变而导致其功能丧失，导致成熟肽的丧失。