CLAVATA3/EMBRYO surrounding region-related (CLE) peptides in legumes that control nodulation and root development

AH Hastwell1, L Corcilius2, M Zhang1, C Jones1, T De Bang3,4, RJ Payne2, PM Gresshoff1 and BJ Ferguson1

  1. Centre for Integrative Legume Research, School of Agriculture and Food Sciences, The University of Queensland, St Lucia, Brisbane, Queensland, 4072, Australia
  2. School of Chemistry, The University of Sydney, Sydney, NSW, 2006, Australia
  3. Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma, 73401, USA
  4. current address: Section for Plant and Soil Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark

Members of the CLAVATA3/EMBRYO SURROUNDING REGION-related (CLE) peptide family are known to play important roles in maintaining meristematic homeostasis in a range of developmental stages and tissue types. We recently identified the complete CLE peptide families of four legume species: soybean, common bean, Medicago truncatula and Lotus japonicus. Legumes are of particular interest as they form an agriculturally and environmentally beneficial symbiosis with soil bacteria, known as rhizobia. CLE peptides are key molecular signals in controlling rhizobia colonising and preventing the bacteria from excessively draining photosynthates and other resources from the host plant. The peptides do this by limiting the number of nodules, specialized root organs that house the rhizobia and enable nitrogen-fixation. In addition to the nodulation CLE peptides, an orthologue of the well characterised AtCLE40 peptide has been identified and characterised in soybean. The expression of GmCLE40 is similar to that of AtCLE40, and peptide application results in a short-root phenotype, as is seen in Arabidopsis. The CLE40 signalling pathway is highly similar to that of the CLV3 pathway. It is reported that CLV3 is post translationally modified with a tri-arabinose moiety at the central hydroxyproline, and due to having a similar amino acid motif, this is also likely to occur in CLE40; however, CLE peptides are difficult to isolate and detect and post-translational modifications have not yet been reported for CLE40. Using synthesis and feeding studies in soybean, the effect of the tri-arabinose moiety on the GmCLE40 peptide was examined in relation to root growth and the expression of GmWOX5 and GmCLE40a. Experiments examining the effect of feeding nodulation CLE peptides modified with the tri-arabinose moiety have also been conducted. Results of these experiments, along with those relating to other members of the legume CLE peptide family, will be discussed.