Populus trichocarpa PtHSFA4a Enhances Heat Tolerance by Regulating Expression of APX1 and HSPs

Abstract

Heat stress can severely inhibit plant growth and reproduction, resulting in heavy financial and crop yield losses. Heat shock transcription factors (HSFs) play an important role in regulating plant responses to abiotic stress. However, compared with the in-depth study of HSF gene function in herbaceous species, reports on the regulatory mechanism of the response of HSFs to heat stress in trees are scarce. Here, we demonstrated that PtHSFA4a is induced by high temperatures in Populus trichocarpa leaves. Intense GUS activity was detected in the leaves of PtHSFA4a promoter-GUS reporter transgenic line under heat stress. Ectopic expression of PtHSFA4a in Arabidopsis thaliana enhanced heat stress tolerance, which reduced malondialdehyde and reactive oxygen species levels. RT-qPCR revealed that the expression of key heat stress-related genes (that is, AtMBF1c, AtZAT12, AtAPX1, AtHSA32, and AtHSPs) was upregulated in PtHSFA4a transgenic plants. Additionally, PtHSFA4a directly bind to the promoters of AtAPX1 and AtHSPs under heat stress to enhance heat tolerance by upregulating the antioxidant defense system and maintaining protein folding homeostasis in A. thaliana leaves. These findings provide novel insights into the molecular mechanisms underlying PtHSFA4a-mediated regulation of plant responses to heat stress.