The heat stress (HS) response is a highly conserved response characterized primarily by rapid induction of heat shock proteins (HSPs) and is regulated by heat shock transcription factors (Hsfs). The HS response is also closely associated with accumulation reactive oxygen species (ROS) and oxidative damage and acclimation of plants to elevated temperatures involves induction of activation of ROS scavenging enzymes in addition to activation of HSPs. Recently we have shown that ROS production and signals are required for the HS response in Arabidopsis, having a novel role in mediating systemic HS responses. Nevertheless, the role of ROS metabolism and signaling in HS-perception and HS-acclimation in plants is still poorly understood. Moreover, the role of ROS scavenging enzymes in HS-signaling and - acclimation is still largely unknown. In this proposal, we will use Arabidopsis plants deficient in the HS-responsive cytosolic ascorbate peroxidases (cAPXs) to study the relationship between cytosolic H2O2 metabolism and systemic HS signaling, and explore the contribution of APX1, 2 and 6 to HS sensing and HS acclimation. Our long-term goal is to elucidate ROS-mediated systemic signaling events triggered by abiotic stress stimuli and identify genes and mechanisms that confer systemic acquired acclimation (SAA) to the stresses.Specific objectives1. Study the function of the cAPXs in the heat stress response Arabidopsis thaliana.2. Unravel the role of cytosolic H2O2 metabolism in systemic heat stress signaling.3. Use cAPX mutants to determine whether heat shock transcription factors (HsfA2 and HsfA4a) are direct sensors of ROS.Impact: The use of cAPX mutants as an experimental platform and our novel experimental approach would further advance the new field of systemic HS acclimation. Elucidating the involvement of ROS signals in HS acclimation would have a profound impact on agriculture and would provide new approaches to improve crop tolerance and yield.