PsHSFB2b regulates thermotolerance in tree peony (Paeonia suffruticosa) through interaction with PsMBF1c

Heat stress stands as a critical factor affecting the growth and development of tree peony ( Paeonia suffruticosa ), leading to a decline in its economic value and ornamental quality, and limiting its wider cultivation in southern regions of China. Previously, we identified a key candidate heat shock transcription factor, PsHSFB2b, potentially regulating thermotolerance in tree peony. In the present study, the PsHSFB2b gene exhibits high sequence conservation and functions as a nuclear-localized protein participating in heat stress response in tree peony. Arabidopsisthaliana plants overexpressing PsHSFB2b exhibited severe cell membrane damage and chloroplast structural disruption, along with reduced ROS scavenging capacity under heat stress. Concurrently, expression levels of related heat stress-responsive genes AtMBF1c , AtHSFB2a , AtHSFB1 , AtHSFA2 , AtHSFA7a , and AtHSP70 were differentially downregulated. PsHSFB2b -silenced tree peony plants exhibited enhanced thermotolerance under heat stress by alleviating cell membrane damage, elevating antioxidant enzyme activity, and accumulating osmolytes. Notably, yeast two-hybrid (Y2H) and luciferase complementation assay (LCA) confirmed a protein-protein interaction between PsHSFB2b and PsMBF1c. PsMBF1c -overexpressing Arabidopsis plants exhibited significantly enhanced thermotolerance, with upregulated expression of heat-responsive genes AtDREB2A , AtHSP70 , AtHSFA3 , AtHSFB2a , AtHSFB2b , and AtWRKY39 . Conversely, silencing PsMBF1c in tree peony reduced heat tolerance, with coordinated expression changes between PsHSFB2b and PsMBF1c in silenced plants. Furthermore, promoter cis-acting element analysis revealed that PsHSFB2b and PsMBF1c contain heat shock elements (HSEs), specific DNA-binding motifs, and regulatory elements responsive to high temperature, oxidative stress, and hormones. These results imply that PsHSFB2b likely regulates thermotolerance in tree peony by interacting with PsMBF1c and participating in related signal transduction pathways.