Transcriptomic and Genomic Insights into HSP-Mediated Protein Homeostasis in Ulmus parvifolia under Temperature Stress

Background : Ulmus parvifolia exhibits strong adaptability to temperature fluctuations; however, its underlying molecular mechanisms remain largely unclear. Heat shock proteins (HSPs) act as key molecular chaperones in plant heat stress responses, yet their evolutionary features and functional roles in U. parvifolia have not been systematically investigated. Results : Transcriptome analysis of root, stem, and leaf tissues under high- and low-temperature treatments revealed pronounced tissue-specific responses to temperature stress. Under high temperature, pathways associated with protein processing in the endoplasmic reticulum and HSP-mediated protein folding and homeostasis were significantly activated, while several energy-consuming secondary metabolic processes were suppressed. In contrast, low-temperature responses were mainly characterized by enhanced oxidative phosphorylation, ribosome activity, and the accumulation of sugars and flavonoids, contributing to energy maintenance and oxidative balance. Weighted gene co-expression network analysis showed that aboveground tissues exhibited stronger responses to heat stress than roots and formed distinct regulatory modules. Genome-wide analysis identified 63 UpHSP genes classified into seven subfamilies, among which HSP70 (25 members) and HSP40 (16 members) showed significant expansion, primarily driven by tandem duplication. Comparative analysis further indicated that HSP70, HSP40, and HSP20 subfamilies are widely expanded across plant species, with more pronounced expansion in Ulmus , suggesting their potential roles in temperature adaptation. Conclusions : Ulmus parvifolia responds to heat stress primarily through activation of HSP-mediated protein folding and homeostasis pathways, accompanied by metabolic adjustment and tissue-specific regulation. This study provides a comprehensive transcriptomic and genomic framework for understanding temperature adaptation in Ulmus and highlights the central role of the HSP gene family in heat tolerance.