PgZHD18-PgWDR5b increases basal thermotolerance in Physalis grisea by lignin biosynthesis dependent on H3K4me3

Physalis grisea is a widely valued orphan crop with medicinal properties and edible functional fruits. Under global warming, high temperature stress (HTS) severely restricts the growth and development of P. grisea, while the epigenetic regulatory mechanism underlying its HTS response remains largely unclear. In this study, we identified the ZINC FINGER HOMEODOMAIN (ZHD) transcription factor PgZHD18 as a positive regulator of basal thermotolerance in P. grisea. Functional assays showed that PgZHD18 enhances basal thermotolerance by improving ROS scavenging capacity, alleviating membrane damage, and maintaining chlorophyll stability. Further molecular verification revealed that PgZHD18 directly binds to the promoters of key lignin biosynthetic genes (PgPAL1, PgC3H1, PgC4H, PgCAD3) and activates their transcription, thus promoting lignin accumulation. Moreover, PgZHD18 interacts with the Trithorax Group (TrxG) protein PgWDR5b, which increases H3K4me3 deposition at the promoters of lignin biosynthetic genes and further amplifies their transcriptional activation, synergistically enhancing basal thermotolerance. Collectively, our findings reveal a dual regulatory module of transcriptional activation coupled with epigenetic modification in plant heat response, and provide a theoretical basis and molecular targets for breeding heat-resistant crop varieties.