Hastwell April H, Gresshoff Peter M, Ferguson Brett J
Centre for Integrative Legume Research, School of Agricultural and Food Sciences, The University of Queensland, St Lucia, Brisbane, Qld 4072, Australia.
Funct Plant Biol. 2015 Mar;42(3):229-238. doi: 10.1071/FP14222.
Legumes form a highly-regulated symbiotic relationship with specific soil bacteria known as rhizobia. This interaction results in the de novo formation of root organs called nodules, in which the rhizobia fix atmospheric di-nitrogen (N2) for the plant. Molecular mechanisms that regulate the nodulation process include the systemic 'autoregulation of nodulation' and the local nitrogen-regulation of nodulation pathways. Both pathways are mediated by novel peptide hormones called CLAVATA/ESR-related (CLE) peptides that act to suppress nodulation via negative feedback loops. The mature peptides are 12-13 amino acids in length and are post-translationally modified from the C-terminus of tripartite-domain prepropeptides. Structural redundancy between the prepropeptides exists; however, variations in external stimuli, timing of expression, tissue specificity and presence or absence of key functional domains enables them to act in a specific manner. To date, nodulation-regulating CLE peptides have been identified in Glycine max (L.) Merr., Medicago truncatula Gaertn., Lotus japonicus (Regel) K.Larsen and Phaseolus vulgaris L. One of the L. japonicus peptides, called LjCLE-RS2, has been structurally characterised and found to be an arabinosylated glycopeptide. All of the known nodulation CLE peptides act via an orthologous leucine rich repeat (LRR) receptor kinase. Perception of the peptide results in the production of a novel, unidentified inhibitor signal that acts to suppress further nodulation events. Here, we contrast and compare the various nodulation-suppressing CLE peptides of legumes.
豆科植物与被称为根瘤菌的特定土壤细菌形成高度调控的共生关系。这种相互作用导致根器官——根瘤的从头形成，根瘤菌在其中为植物固定大气中的双氮（N₂）。调节结瘤过程的分子机制包括系统性的“结瘤自调控”和结瘤途径的局部氮调控。这两条途径均由一种名为CLAVATA/ESR相关（CLE）肽的新型肽激素介导，它们通过负反馈环来抑制结瘤。成熟肽长度为12 - 13个氨基酸，是从三方结构域前体肽的C末端经翻译后修饰而来。前体肽之间存在结构冗余；然而，外部刺激、表达时间、组织特异性以及关键功能域的有无等方面的差异，使它们能够以特定方式发挥作用。迄今为止，已在大豆（Glycine max (L.) Merr.）、蒺藜苜蓿（Medicago truncatula Gaertn.）、百脉根（Lotus japonicus (Regel) K.Larsen）和菜豆（Phaseolus vulgaris L.）中鉴定出调节结瘤的CLE肽。百脉根中的一种肽，名为LjCLE-RS2，已进行了结构表征，发现它是一种阿拉伯糖基化糖肽。所有已知的调节结瘤的CLE肽均通过直系同源的富含亮氨酸重复序列（LRR）受体激酶发挥作用。对该肽的感知会产生一种新型的、未明确的抑制信号，该信号可抑制进一步的结瘤事件。在此，我们对豆科植物中各种抑制结瘤的CLE肽进行对比和比较。
