Overexpression of PeHSF mediates leaf ROS homeostasis in transgenic tobacco lines grown under salt stress conditions

Transcriptional responses of a heat-shock transcription factor from the salt-resistant Populus euphratica, PeHSF, were assessed in transgenic tobacco seedlings subjected to salinity stress. Moreover, their relevance to NaCl-induced anti-oxidative defense responses in higher plants was also explored. Expression of PeHSF was induced by high-salinity (150 mM NaCl) in leaves and callus cultures of P. euphratica. The salt-stimulated PeHSF expression in P. euphratica callus cultures was markedly inhibited by DPI (an inhibitor of plasma membrane NADPH oxidase) and LaCl3 (an inhibitor of plasma membrane Ca2+-permeable channels), indicating the involvement of reactive oxygen species (ROS) and Ca2+ in HSF activation under NaCl stress. Sequence analysis showed that PeHSF is a typical class A HSF in higher plants. PeHSF overexpression in tobacco significantly improved the salt tolerance of transgenic plants, in term of seed germination and root growth. Compared to the wild-type plants, the PeHSF-transgenic lines exhibited an increased capacity to control ROS homeostasis, but not an enhanced capacity to retain ionic homeostasis under salt stress. PeHSF expression in tobacco enhanced the activities of ascorbate peroxidase, glutathione peroxidase, and glutathione reductase, due to upregulated transcriptional levels. We conclude that PeHSF plays a crucial role in ROS detoxification under salt stress, rather than in maintenance of the K+/Na+. It is likely that the salt-induced H2O2 and cytosolic Ca2+ led to transcriptional activation of HSF, which initiated the transcription of genes encoding antioxidant enzymes in P. euphratica, thus contributing to ROS homeostasis control under saline conditions.