Exogenous Salicylic Acid Regulates Fruiting Body Development, Secondary Metabolite Accumulation, Cell Wall Integrity, and Endogenous Salicylic Acid Content under Heat Stress in <i>Pleurotus ostreatus</i>

High-temperature or heat stress (HS) represents a significant environmental challenge that adversely affects crop growth and poses a substantial threat to agricultural production. <i>Pleurotus ostreatus</i>, recognized as the second most widely cultivated edible fungus worldwide, is particularly susceptible to the detrimental effects of HS. Enhancing the HS resistance of <i>P. ostreatus</i> is crucial for increasing its yield. In a prior investigation, we discovered that salicylic acid (SA) enhanced the resistance of <i>P. ostreatus</i> mycelia to HS through a metabolic rearrangement. The present study further investigated the effects of SA on <i>P. ostreatus</i> under HS. Cultivation experiments revealed that exogenous SA improved the mycelium recovery growth rate, yield, and fruiting body quality after HS. Further experiments revealed that exogenous SA mitigated the damage to the MAPK-Slt2 signal produced by HS while maintaining cell wall integrity. Furthermore, we hypothesized that the phenylalanine ammonia-lyase pathway might serve as a source for SA. In this context, we identified two salicylic hydroxylases, Po1102164 and Po1104438. Both HS and exogenous SA were found to elevate intracellular SA levels, thereby enhancing the resistance of <i>P. ostreatus</i> to HS.