Abstract
Histidine kinases (HKs) are involved in the perception of osmotic stress in cyanobacteria and yeast. We previously demonstrated that HKs AHK1 and AHK2/3 function as positive and negative regulators in osmotic stress responses in Arabidopsis, respectively, and suggested the involvement of HKs in the perception of osmotic stress. To clarify whether HKs-mediated osmotic stress responses are ubiquitous in higher plants, we focused on the roles of rice HKs in osmotic stress responses.
Through homology searches against the rice genome, we found four close homologs of cytokinin receptor genes (OsHK3, OsHK4, OsHK5 and OsHK6), but could not find any AHK1 homologs.Then, we cloned the ORFs of each OsHK gene and tested their functions in yeast cells. In complementation tests of yeast mutants, OsHK3, OsHK4, OsHK5 and OsHK6 could function as cytokinin receptors, and OsHK6 could function as an osmosensor in a cytokinin dependent manner.
Now we are analyzing the response of OsHK-overexpressing rice to cytokinin or osmotic stress treatments. The roles of these histidine kinases in rice will be discussed.
