Abstract
An Arabidopsis mutant, itn1, is less sensitive to exogenous abscisic acid (ABA) than wild type plants. ITN1 encodes a plasma-membrane protein with an ankyrin-repeat motif which is implicated in protein-protein interactions. In order to clarify the molecular function of ITN1, we searched interacting partners of ITN1 by yeast two-hybrid screening. As a result, a putative transcription factor, RTV1, was identified as one of candidate proteins. Bimolecular fluorescence complementation analysis shows that RTV1 interacts with ITN1 at the plasma membrane in onion epidermal cells. In an Arabidopsis mutant deficient in RTV1, the ABA induction of PR1, known as a stress-responsive gene, occurred earlier than that in wild-type plants. By contrast, in the itn1 mutant, the ABA-induced expression of PR1 was suppressed. These suggests that RTV1 represses the PR1 expression at an early stage of ABA response, and that ITN1 induces the PR1 expression by interacting with RTV1 and inhibiting its activity at the later stage. Possible functions of the interaction between ITN1 and RTV1 in the ABA response will be discussed.
