SlbHLH36-SlAAP8 alleviates heat-induced pollen abortion by regulating amino acid metabolism in tomato

Under environmental stress, plants dynamically reprogram amino acid metabolism and long-distance transport to facilitate efficient nutrient reallocation. However, amino acid transporters in tomato remain poorly characterized, especially with respect to their functional roles, transcriptional regulation, and influence on pollen fertility under heat stress. In this study, a metabolite-based genome-wide association study identifies an amino acid transporter, amino acid permease 8 (SlAAP8), that is significantly associated with the content of multiple amino acids. SlAAP8 is primarily expressed in tomato flowers and exhibits broad-spectrum amino acid transport activity. Overexpression of SlAAP8 (SlAAP8-OE) promotes amino acid accumulation in stamen tissues and enhances pollen viability under high-temperature conditions. Furthermore, we identify a transcription factor, SlbHLH36, that directly binds to the E-box (CANNTG) motif in the SlAAP8 promoter and activates its transcription. Heat stress significantly upregulates the expression of both SlbHLH36 and SlAAP8, thereby improving pollen viability under high-temperature conditions by modulating amino acid metabolism and antioxidant activity, as well as reducing malondialdehyde accumulation. Together, these findings suggest that the SlbHLH36-SlAAP8 module enhances tomato pollen viability under heat stress through regulating amino acid metabolism and scavenging reactive oxygen species, providing a potential avenue to improve crop yields under global warming.