A multitude of signals converge on SUNN to regulate nodule number
J. FRUGOLI (1), A. Crook (1), S. Nowak (1), E. Schnabel (1) (1) Clemson University, U.S.A.

Autoregulation of nodulation (AON) is a signalling pathway in legumes which limits the number of nodules formed in the rhizobia-legume symbiosis. In Medicago truncatula, this systemic regulation includes local signalling events resulting in the induction of 2 CLE genes in the nodule meristem, MtCLE12 and MtCLE13, presumed to regulate nodule number through translocation of the peptides to the shoot, where they bind a receptor complex containing the LRRR kinase SUNN; subsequent signal transduction results in termination of nodule initiation. Several lines of evidence suggest post-translational addition of a tri-arabinose chain to a hydroxyproline in some CLE peptides by a HPAT enzyme is necessary for receptor binding. We previously showed the RDN1 gene (an HPAT) regulates nodule number. In order to determine specificity of the modification, we have shown that RDN2 is also involved in AON, but not RDN3, and that overexpression of the nodulation CLEs in an rdn1 mutant background has differential effects, supporting a model in which different RDNs modify different CLE peptides. We also identified SUNN receptor complexes and SUNN signalling components that play roles in AON. Two G-protein signalling molecules of the Rop-GEF family and two proteins involved in the CLV signalling pathway in Arabidopsis are all capable of interacting with SUNN. Mutation of these genes results in a hypernodulation phenotype, suggesting the interactions are part of AON signal transduction. Together the data suggest a model in which AON signalling involves multiple SUNN protein complexes and components of a G-protein signalling cascade while RDNs directly modify ligands. Supported by NSF IOS#1146014 and a Clemson Wade Stackhouse Fellowship to A.C. and S.N.

Abstract Number: P2-23
Session Type: Poster