Molecular characterization of a bHLH transcription factor involved in Arabidopsis abscisic acid-mediated response.

The suppression subtractive hybridization (SSH) method was used to isolate abscisic acid (ABA)-regulated genes in Arabidopsis. We report that the AtAIG1 gene is up-regulated by ABA and the AtAIG1 encodes a basic/helix-loop-helix (bHLH)-type transcription factor in Arabidopsis. The AtAIG1 was targeted into nucleus and bound to the E-box-DNA sequence, which is found in the promoter regions of many ABA-responsive genes. Functional analyses with the ataig1 knockout mutants revealed that the mutant plants show enhanced sensitivity to ABA. In addition, the ataig1 plants showed reduced expression of ABA-responsive genes, such as RD29A and RD22. Thus, these functional analyses suggest that the AtAIG1 protein plays an important role in ABA-mediated signal transduction pathway.