Functional analysis of an Arabidopsis transcription factor WRKY25 in heat stress

The WRKY family is one of the major groups of plant-specific transcriptional regulators. Arabidopsis thaliana WRKY25, which is induced by heat stress, is one of the group I WRKY proteins and responds to both abiotic and biotic stress. This study has examined the regulatory role of WRKY25 using wrky25 mutant and over-expressing WRKY25 transgenic A. thaliana. After 45 degrees C for different time periods, wrky25 null mutants showed a moderate increase in thermosensitivity with decreased germination, reduced hypocotyl and root growth, and enhanced conductivity compared to those of wide-type, while WRKY25 over-expressed transgenic seeds exhibited enhanced thermotolerance. Northern blot analysis of wrky25 mutants and WRKY25 over-expressing plants identified putative genes regulated by WRKY25. In consistence with the implication of WRKY25 in heat tolerance, the expression level of six heat-inducible genes and two oxidative stress-responsive genes was more or less down-regulated in wrky25 mutants during heat stress. Among them, heat shock protein Hsp101, heat shock transcription factor HsfB2a, and cytosolic ascrobate peroxidase APX1 were reduced more obviously than other detected genes. Meanwhile, over-expression of WRKY25 increased the expression of HsfA2, HsfB1, HsfB2a, and Hsp101 slightly or moderately. Together, these findings reveal that WRKY25 plays a partial role in thermotolerance.