Water Stress Activates The Expression of Abscisic Acid Transporter, VuABCG25, in Cowpea [Vigna unguiculata (L.)Walp.]

Abstract

Cowpea [Vigna unguiculata (L.) Walp.] is highly adapted to drought conditions and avoids water loss from leaf by closing stomata via abscisic acid (ABA) signaling. Recently, molecular genetic studies in Arabidopsis have revealed that the ABA responses are mediated by various long-distance signals and ABA transport mechanisms. However, it remains unknown whether the transport mechanisms of ABA are involved in significant drought tolerance of cowpea. Here we identified a set of ATP-binding cassette (ABC) transporter gene candidates, VuABCG22, VuABCG25 and VuABCG40 by searching for ABA transporter homologs on cowpea genome database. One VuABCG25, two VuABCG22 and four VuABCG40 were identified in cowpea genome, while those corresponding homologs are single genes in Arabidopsis genome. Semi-quantitative RTPCR analysis indicated that water stress including drought and salinity significantly induced up-regulation of VuABCG25 expression but not VuABCG22 and VuABCG40. Three genes out of four VuABCG40 genes are found in a gene cluster at the chromosome 1 in the cowpea genome. These results strongly suggest that ABArelated ABC transporter genes are highly conserved between cowpea and Arabidopsis and that VuABCG25 is involved in the ABA signaling pathway in cowpea under water stress.