Cytokinin-induced expression of OSH1 in a shoot-regenerating rice callus.

The expression of a KNOX class 1 gene OSH1 is induced by cytokinin during regeneration of shoots from callus in Oryza sativa L. (rice). This cytokinin-induced expression was enhanced by overexpression of homologues of cytokinin-signalling phosphorelay genes such as a histidine kinase gene OHK3, a phosphotransmitter gene OHP2 and a response regulator gene ORR1 in cultured cells. Regionally overlapped expression of these genes and OSH1 was observed in shoot apex. These results suggest that these cytokinin-signalling genes are positive regulators of the expression of OSH1, and mediate the OSH expression upon shoot regeneration from callus in rice.