Volatile organic compounds prime heat tolerance through chromatin-dependent heat shock pathways in Arabidopsis

Volatile organic compounds (VOCs) can prime plants for improved survival under heat stress, yet how chromatin regulation shapes VOC-triggered heat shock responses remains unclear. Here, we analyzed heat and VOC responses in Arabidopsis thaliana Col-0 and the epigenetic mutants ddm1, nrpd1, suvh456, and hda6. In a seven-VOC screen, heat and multiple VOCs induced HSFA2, with trans-2-hexenal (T2H) among the most consistent inducers. Although ddm1 and hda6 showed reduced HSFA2 induction under heat, VOC induction remained strong, indicating that volatile signaling can partially rebalance heat-dependent regulation. Priming with the VOC panel increased survival after lethal heat across genotypes, and phenotype scoring (Healthy/Affected/Dead) revealed genotype-dependent outcome shifts, including a stronger T2H-driven enrichment of Healthy seedlings in hda6. Expression profiling of HSFA1a-e regulators and the downstream chaperone HSP101 indicated intact pathway competence, while revealing quantitative rewiring in hda6. RNA-seq showed that T2H activates a program that is distinct from, but partially overlaps with, the heat response, combining a shared stress core with VOC-biased signaling and reactive oxygen species (ROS)-related modules that are amplified in hda6. Finally, analysis of public ChIP-seq datasets linked altered promoter enrichment of active marks (H3Ac and H3K4me2), particularly at HDA6-bound promoters, to basal transcript output and uneven tuning of VOC- and heat-/ROS-responsive loci. Together, these results support a model in which chromatin regulation tunes both the basal state and inducibility of VOC-responsive stress networks, thereby shaping VOC-primed thermotolerance.