this study was supported by a grant - in - aid for scientific research on priority areas ( 19039013 to t.m . and
20061016 to t.y . ) and a grant - in - aid for the gcoe programs ( systems biology ) of the ministry of education , culture , sports , science , and technology of japan .
 the two - component systems ( tcs ) , or histidine - to - aspartate phosphorelays , are evolutionarily conserved common signal transduction mechanisms that are implicated in a wide variety of cellular responses to environmental stimuli in both prokaryotes and eukaryotes including plants . among higher plants , 
 legumes including lotus japonicus have a unique ability to engage in beneficial symbiosis with nitrogen - fixing bacteria . 
 we previously presented a genome - wide compiled list of tcs - associated components of mesorhizobium loti , which is a symbiont specific to l. japonicus ( hagiwara et al . 
 2004 , dna res . 
 , 11 , 5765 ) . to gain both general and specific insights into tcs of this currently attractive model legume , here we compiled tcs - associated components as many as possible from a genome - wide viewpoint by taking advantage that the efforts of whole genome sequencing of l. japonicus are almost at final stage . in the current database ( http://www.kazusa.or.jp/lotus/index.html ) , it was found that l. japonicus has , at least , 14 genes each encoding a histidine kinase , 7 histidine - containing phosphotransmitter - related genes , 7 type - a response regulator ( rr)-related genes , 11 type - b rr - related genes , and also 5 circadian clock - associated pseudo - rr genes . 
 these results suggested that most of the l. japonicus tcs - associated genes have already been uncovered in this genome - wide analysis , if not all . 
 here , characteristics of these tcs - associated components of l. japonicus were inspected , one by one , in comparison with those of arabidopsis thaliana . in addition , some critical experiments were also done to gain further insights into the functions of l. japonicus tcs - associated genes with special reference to cytokinin - mediated signal transduction and circadian clock . 
Supplementary Data
Funding