Expression of Arabidopsis response regulator homologs is induced by cytokinins and nitrate.

We examined cytokinin and nitrate responsiveness in gene expression of five distinct response regulator homologs (ARR3-ARR7) in the leaves of nitrogen-starved Arabidopsis plants. The transcripts accumulated after spraying the shoots with t-zeatin. The induction of accumulation was highly specific for cytokinins. The transcripts also accumulated by supply of nitrate to the culture medium. These findings suggest that ARRs are involved in inorganic nitrogen signal transduction mediated by cytokinin as in the case of ZmCip1, a response regulator homolog recently identified in maize.