Centre for Integrative Legume Research, School of Agriculture and Food Sciences, The University of Queensland, St Lucia, Brisbane, Queensland, 4072, Australia.
School of Chemistry, The University of Sydney, Sydney, New South Wales, 2006, Australia.
Plant Cell Environ. 2019 Jan;42(1):188-197. doi: 10.1111/pce.13325. Epub 2018 Aug 3.
Legumes form root nodules to house beneficial nitrogen-fixing rhizobia bacteria. However, nodulation is resource demanding; hence, legumes evolved a systemic signalling mechanism called autoregulation of nodulation (AON) to control nodule numbers. AON begins with the production of CLE peptides in the root, which are predicted to be glycosylated, transported to the shoot, and perceived. We synthesized variants of nodulation-suppressing CLE peptides to test their activity using petiole feeding to introduce CLE peptides into the shoot. Hydroxylated, monoarabinosylated, and triarabinosylated variants of soybean GmRIC1a and GmRIC2a were chemically synthesized and fed into recipient Pisum sativum (pea) plants, which were used due to the availability of key AON pathway mutants unavailable in soybean. Triarabinosylated GmRIC1a and GmRIC2a suppressed nodulation of wild-type pea, whereas no other peptide variant tested had this ability. Suppression also occurred in the supernodulating hydroxyproline O-arabinosyltransferase mutant, Psnod3, but not in the supernodulating receptor mutants, Pssym29, and to some extent, Pssym28. During our study, bioinformatic resources for pea became available and our analyses identified 40 CLE peptide-encoding genes, including orthologues of nodulation-suppressive CLE peptides. Collectively, we demonstrated that soybean nodulation-suppressive CLE peptides can function interspecifically in the AON pathway of pea and require arabinosylation for their activity.
豆科植物形成根瘤来容纳有益的固氮根瘤菌。然而，结瘤是资源密集型的；因此，豆科植物进化出了一种称为结瘤自动调节（AON）的系统信号机制来控制根瘤的数量。AON 始于根中 CLE 肽的产生，这些肽预计被糖基化，被运输到地上部分并被感知。我们合成了结瘤抑制 CLE 肽的变体，以通过叶柄喂养将 CLE 肽引入地上部分来测试它们的活性。大豆 GmRIC1a 和 GmRIC2a 的羟基化、单阿拉伯糖基化和三阿拉伯糖基化变体被化学合成，并喂食给受体豌豆（豌豆）植物，由于缺乏在大豆中不可用的关键 AON 途径突变体，因此使用了这些植物。三阿拉伯糖基化的 GmRIC1a 和 GmRIC2a 抑制了野生型豌豆的结瘤，而没有其他肽变体具有这种能力。在羟脯氨酸 O-阿拉伯糖基转移酶突变体 Psnod3 中也发生了抑制，但在超级结瘤受体突变体 Pssym29 中没有发生抑制，在某种程度上，Pssym28 也没有发生抑制。在我们的研究过程中，豌豆的生物信息学资源变得可用，我们的分析确定了 40 个 CLE 肽编码基因，包括结瘤抑制 CLE 肽的同源物。总的来说，我们证明了大豆结瘤抑制 CLE 肽可以在豌豆的 AON 途径中种间发挥作用，并且需要阿拉伯糖基化才能发挥活性。
