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 PIF1, driving us to name the transcription factor OsPIF1. Overexpression of OsPIF1 in transgenic rice 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, the transcription of a GUS reporter gene driven by the promoter containing G-box elements was activated by OsPIF1, suggesting that OsPIF1 acts as a transcriptional activator. 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 using 44k rice oligoarray with OsPIF1 transgenic rice plants.
