Abstract
Using a rice microarray, we identified many abiotic stress-responsive genes. Among them, a gene for a bHLH transcription factor down-regulated by drought stress has been studied. The bHLH protein showed a high sequence homology with Arabidopsis PIF, driving us to name the transcription factor OsPIF1. Overexpression of OsPIF1 in transgenic rice plants promoted internode elongation. In contrast, dominant loss-of-function rice mutants with a chimeric repressor resulted in short length of the internode sections. In a transient experiment using rice protoplasts, the transcription of a GUS reporter gene driven by the promoter containing G-box elements was activated by OsPIF1 and we found that the APB motif of OsPIF1 is important for this activation. These data suggest that OsPIF1 functions as an important regulatory factor of plant growth in response to drought stress. Currently, we are analyzing down-stream genes of OsPIF1 by an oligoarray system using OsPIF1 transgenic rice plants.
