We isolated 76 high-light and heat-shock (HL + HS) stress-inducible genes, including a putative heat-shock transcription factor (HsfA2), by suppression-subtractive hybridization from Arabidopsis. The transcript level of HsfA2 was significantly increased under the several stress conditions or by the H(2)O(2) treatment. Furthermore, the induction of HsfA2 expression was highest among those of other class A HSFs in response to HL + HS stress conditions. The promoter assay revealed that HsfA2 is induced mainly in rosette leaves under HL + HS stress conditions. In the HsfA2-overexpressing Arabidopsis (Pro(35S):HsfA2) plants, 46 genes, including a large number of heat-shock proteins, ascorbate peroxidase 2 and galactinol synthase 1 and 2, were highly expressed compared with those in the wild-type plants. The transcript levels of the HsfA2 target genes are highly correlated with those of HsfA2 in the Pro(35S):HsfA2 plants. The transcript levels of the HsfA2 target genes, as well as HsfA2 transcripts, were induced by treating with exogenous H(2)O(2). In the knockout HsfA2 Arabidopsis plants, the induction of 26 HsfA2 target genes was strongly reduced for up to 2 h under HL + HS stress conditions. Furthermore, the Pro(35S):HsfA2 plants showed increased tolerance to combined environmental stresses. Our present results indicate that HsfA2 is a key regulator in the induction of the defence system under several types of environmental stress.