Abstract
SYMRK (symbiosis receptor-like kinase) was cloned from the legume, Lotus japonicus, as a gene required for both symbioses between plant and Rhizobia, and arbuscular mycorrhizal fungi. This gene encodes a LRR-type receptor kinase, featuring a signal peptide, 3 LRR motifs, a transmembrane domain and a Ser/Thr kinase domain.
Several symbiosis-deficient symrk mutant alleles from Lotus and Pea have mutations at the conserved residues of the kinase domain, suggesting kinase activity is important for SYMRK biological function. To investigate the regulatory mechanism of the SYMRK kinase activity, we expressed the kinase domain of SYMRK in E. coli and observed its auto-phosphorylation activity. Moreover, in gel and in vitro kinase assay results indicate that the phosphorylation status of SYMRK affects its kinase activity, i.e. SYMRK requires phosphorylation to gain a full kinase activity. Targeting mutagenesis and Q-Tof analysis identified the Ser/Thr residues important for regulation of the SYMRK kinase activity.
