Phenotypic characterization of nod- mutants transformed with a gain-of-function CCaMK

Abstract

Recent studies of symbiotic mutants of Lotus japonicus have led to isolation of a number of host genes, which are required for endosymbioses with both rhizobia and arbuscular mycorrhiza. These genes compose a common signaling pathway (CSP), in which symbiotic signals are converted into Ca signals (Ca-spiking). CCaMK, Ca/CaM-dependent protein kinase, also belongs to CSP and may act as a Ca decoder. Ca binding to CCaMK leads to activation of downstream pathways responsible for endosymbioses. Introduction of gain-of-function (gof) CCaMK leads to formation of spontaneous nodule. This fact indicates a pivotal role of CCaMK for nodule organogenesis.
During nodule formation, nodule organogenesis is coupled with bacterial infection. To clarify the involvement of several symbiotic genes in nodule organogenesis and/or bacterial infection, we introduced gof-CCaMK into nod- mutants and analyzed symbiotic phenotypes of them. Based on the results, we propose a model of early signaling pathway of nodulation.