LIGHT AND NUTRITIONAL REGULATION OF TRANSCRIPTS ENCODING A WHEAT-PROTEIN KINASE HOMOLOG IS MEDIATED BY CYTOKININS

Many metabolic processes in plants are regulated by phosphorylation of proteins by kinases, but little is known of the roles that specific p rotein kinases play in the various signal transduction pathways or the mechanisms by which these kinases themselves are regulated. We report here the isolation of a gene, wpk4, encoding a putative protein kinas e from wheat that appears to belong to the SNF1 kinase subfamily and t hat shows increased transcript levels in response to multiple stimuli: light, nutrient deprivation, and cytokinin application. Although wpk4 mRNA is undetectable in etiolated seedlings, it rapidly accumulates w ithin 1 hr of illumination. General nutrient deprivation also increase s wpk4 mRNA levels, but only under light conditions. In addition, of t he various phytohormones tested, cytokinin (N6-benzylaminopurine) spec ifically increases wpk4 mRNA levels regardless of the light conditions , whereas in the presence of a cytokinin antagonist the level of wpk4 mRNA is not increased by either light or nutrient deprivation. These r esults suggest that the light and nutrient signals that induce wpk4 mR NA accumulation may be mediated through cytokinins and provide a stron g basis for examining the coordinated regulation of protein phosphoryl ation by light, cytokinins, and nutritional cues in a single transduct ion pathway.