Abstract
The ethylene receptors, cytokinin receptors, and phytochromes are composed of N-terminal signal-sensing domain and C-terminal signal-output domain containing histidine kinase or histidine kinase-related kinase. Some bacteria have the genes consisting of the similar domain architecture. Therefore, these plant receptors might be descendants of bacterial progenitor. However, the current phylogenetic analysis using the sequences of kinase domains provides no evidence supporting the monophyletic origins of these receptors. Several evidences suggest that the recombination between the kinase domain and signal-sensing domain has not been rare event. I propose here that these plant receptors represent mosaics of domains with different evolutionary history.
