A PebZIP44-PeHSF12-PeHSP17.8 transcriptional module controls heat shock protein expression and thermotolerance in passion fruit(Passiflora edulis).

Heat stress is a major constraint for passion fruit (Passiflora edulis) production, yet the transcriptional mechanisms underlying thermotolerance in this perennial vine remain poorly understood.This study identified 15 HSF genes (PeHSFs) in Passiflora edulis (P. edulis) genome. Phylogenetic analysis classified these PeHSFs into three distinct clusters containing 9, 4, and 2 genes, respectively, with conserved structural features supporting their functional divergence.Tissue-specific expression profiling demonstrated significant organ-dependent expression patterns of PeHSFs across roots, stems, leaves (young/mature), flowers, and fruits. Here, we report a heat shock transcription factor PeHSF12, which integrates upstream signals from a bZIP transcription factor to orchestrate downstream heat shock protein expression. Through a combination of DAP-Seq, EMSA and dual-luciferase assays, we demonstrated that PeHSF12 directly binds to the heat shock element in the promoter of PeHSP17.8, a small HSP critical for protein stability under thermal stress. Crucially, we identified PebZIP44 as an upstream transcriptional repressor of PeHSF12, whose expression is down-regulated under heat, thereby de-repressing PeHSF12 and activating the heat response pathway. Functional validation using heterologous overexpression in Arabidopsis and virus-induced gene silencing (VIGS) in passion fruit seedlings confirmed that PeHSF12 enhances thermotolerance through bolstering antioxidant capacity and reducing oxidative damage. This study unveils a previously uncharacterized PebZIP44-PeHSF12-PeHSP17.8 module in passion fruit, providing both mechanistic insight into heat adaptation in P. edulis and a candidate gene resource for breeding heat resistance cultivars.