Abstract
Regulatory mechanisms of stress responses in rice largely remain unclear, compared to those in Arabidopsis. 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. Transgenic Arabidopsis plants overexpressing OsPIF1 and dominant loss-of-function Arabidopsis mutants with the chimera repressor changed growth rates and drought stress tolerances, suggesting that OsPIF1 functions as an important growth regulatory factor in response to drought stress in rice. Here, we generated transgenic rice plants overexpressing OsPIF1 and dominant loss-of-function rice mutants with the chimera repressor. The former displayed long length grains and giant culms with elongated internodes. The latter exhibited conversely short length grains and dwarf culms with short internodes. Currently, we are analyzing target genes for OsPIF1.
