Analysis of the regulation of target genes by an Arabidopsis heat shock transcription factor, HsfA2.

We have isolated a high-light and heat-shock inducible gene, Arabidopsis heat shock transcription factor (HsfA2), which induces expression of various types of target gene such as heat shock protein 18.2-CI (Hsp18.1-CI), galactinol synthase 1 (GolS1), and Bcl-2-associated athanogene 6 (Bag6). Here we investigated the regulatory system of target genes operating via HsfA2. A transient reporter assay using a luciferase reporter construct with different fragments of the Hsp18.1-CI, the GolS1, or the Bag6 promoter showed that two modules of a TATA-proximal heat shock element (HSE) are essential for transcriptional activation by HsfA2. Electrophoretic mobility shift assay demonstrated that the increase in protein complex formation onto the HSE was markedly suppressed during high-light stress and recovery from the stress in knockout HsfA2 plants. HsfA2 appears to function not only in the triggering of response to environmental stress, but also in the amplification of the signal in the response.