Abstract
The two-component systems (TCS) are a mode of widely conserved signal transduction in plants. The best-characterized representative of plant TCS is the mechanism underlying cytokinin responses,in which His-kinases function as the hormone receptor. Although these ideas came from extensive studies on Arabidopsis thaliana, certain plant species belonging to legume are currently of much interest, because it was found that the formation of beneficial nodules is regulated somehow through the CK receptor His-kinase, named LHK1.We are currently characterizing the Lotus japonicus TCS from the genome-wide viewpoint. For instance, we now know that (i) L. japonicus has three CK receptor His-kinases (LHK1/2/3), as does A. thaliana. (ii) In addition to type-A RRs, LHK1 and one of B-type RR, named LjRRb2 are specifically induced by CK in roots. Taking these together, we are examining roles of L. japonicus TCS factors in nodulation through reverse genetics by adopting the method of transformed hairy-root formation. We will discuss about these results in the context of current knowledge about the genetic networks underlying the nodule formation.
