Abstract
Heat shock transcription factors (HSFs) are widely conserved among eukaryotes and function in heat stress responses. Although animals and yeast have only one to several HSF genes, plants have many HSFs divided into three classes (A, B and C) according to the structural features of their oligomerization domains. B-class HSF proteins (HSFBs) are plant specific and their functions are unknown. We investigated their functions in the heat stress responses using Arabidopsis plants. Arabidopsis has 21 HSFs including 5 HSFBs. We found that the HSFB1, HSFB2A and HSFB2B genes are heat-inducible and these HSFBs have repressor activity in the transient expression assay using Arabidopsis protoplasts. Thus we assumed that these HSFs act as transcriptional repressors and regulate heat stress responses by tuning or decreasing heat-inducible gene expression. Then we generated transgenic plants overexpressing each HSFB gene and knock out mutant plants and analyzed the expression patterns of heat-inducible genes in these transgenic and mutant plants under heat stress condition.
