JA regulates the impact of combined heat stress and drought stress on the GA-mediated response of Pinus yunnanensis

The ongoing climate change phenomenon has been shown to lead to an increased frequency of extreme weather events, including heatwaves and droughts. These conditions have been found to present considerable challenges to the survival of plants and the stability of ecosystems. Pinus yunnanensis , a conifer native to subtropical regions, faces challenges due to prolonged seedling periods and sensitivity to abiotic stresses. This study examines the function of jasmonate (JA) in alleviating the synergistic impacts of heat stress (HS) and drought stress (DS) on P. yunnanensis seedlings, with a focus on its interaction with gibberellin (GA)-mediated growth responses. Exogenous applications of JA, GA, and their combination were observed to result in a reduction of wilting, an increase in chlorophyll content, and enhanced antioxidant enzyme activities (CAT and POD) in JA-treated seedlings when compared to GA-treated and control groups. Physiological analyses revealed stable soluble sugar levels and dynamic proline accumulation in JA-treated seedlings, suggesting a reallocation of resources toward stress defense. A series of molecular studies were conducted, the results of which identified several key genes ( DELLA , JAZ , GA2ox , and MYC2 ) that are involved in phytohormone signaling. The findings of these studies indicated that JA+GA co-treatment resulted in the upregulation of DELLA and JAZ expression. This, in turn, indicated crosstalk between the GA and JA pathways. Phylogenetic and bioinformatics analyses confirmed the evolutionary conservation of these stress-responsive genes. The present study demonstrates that JA enhances stress tolerance by modulating antioxidant activity and hormone signaling, while GA promotes growth at the expense of defense. The present study offers insights into the growth-defense trade-offs in P. yunnanensis and highlights the potential of JA applications to improve forest resistance under the combination of HS+DS. • JA enhances stress tolerance in Pinus yunnanensis under combined heat and drought by boosting antioxidant activity (CAT, POD) and chlorophyll retention. • GA-JA crosstalk modulates growth-defense balance, with JA+GA co-treatment stabilizing soluble sugar and proline dynamics under stress. • Key genes ( DELLA , JAZ , GA2ox , MYC2 ) have been revealed to be involved in phytohormone signaling pathways, thus establishing a link between stress adaptation and phytohormone regulation. • Exogenous JA application improves Pinus yunnanensis resistance by prioritizing defense over growth, offering a climate adaptation strategy.