Abstract
The drought-responsive expression of an Arabidopsis gene, rd29B, is mainly mediated by phytohormone abscisic acid (ABA). Two ABREs play a crucial role in the expression of rd29B as cis-elements. bZIP-type ABRE binding proteins, AREBs function as transcriptional activators in the expression of rd29B in vegetative tissues. Transactivation analysis by using ABA mutants, in-gel kinase activity assay and amino-acid substitution analysis of AREBs indicated that the transactivation activity of AREBs is regulated by ABA-responsive serine/threonine kinases.
A receptor-like kinase, RPK1, is a member of LRR-RLK families of Arabidopsis. Repression of RPK1 expression in Arabidopsis plants resulted in decrease of sensitivity to ABA in the various physiological events, including germination, growth rate, stomatal closure and gene expression. Microarray analysis showed that the many ABA-inducible genes including AREB1 are down-regulated in the rpk1 mutants, indicating that RPK1 has an important role in the main pathway of ABA signaling in Arabidopsis.
