HSFs are essential in plants’ ability to both sense and respond to stress.
[5] The HSFs, which are divided into three families (A, B, and C), encode the expression of heat shock proteins (HSP).
Past studies have found that transcriptional activators HsfA1 and HsfB1 are the main positive regulators of heat stress response genes in Arabidopsis thaliana.
They used RT-PCR to analyze the expression of HS-inducible genes of mutant (ectopic and nonfunctional HsfB1) and wild type plants.
With these results they concluded that class A HSFs positively regulated the heat stress response while class B HSFs repressed the expression of HSF genes.