Abstract
Regulatory mechanisms of stress responses in rice largely remain unclear. Using 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. These data suggest that OsPIF1 functions as an important regulatory factor of plant height in response to drought stress. Recently, we analyzed down-stream genes of OsPIF1 by oligoarray system using node sections of OsPIF1 transgenic rice plants. Those putative down-stream genes of OsPIF1 were down-regulated by drought stress. In a transient experiment using rice protoplasts prepared from shoots, the transcription of a GUS reporter gene driven by the promoter containing E-box elements was activated by OsPIF1.
