SlMYB30 relieves high vapor pressure deficit stress by modulating salicylic acid biosynthesis and stomatal morphology in tomato

High vapor pressure deficit (HVPD) stress presents challenges to global agriculture, impacting crop productivity, water resource management, ecosystem stability, and food security. Tomato (Solanum lycopersicum L.) is an economically important crop grown extensively around the world; however, the molecular mechanisms that enable its resistance to HVPD stress are not yet fully understood. In this study, V-MYB AVIAN MYELOBLASTOSIS VIRAL ONCOGENE HOMOLOG 30 (SlMYB30), an R2R3-type MYB transcription factor responsive to HVPD stress in tomato, was identified through transcriptomic and metabolomic analyses. We examined the role of SlMYB30 in conferring resistance to HVPD stress using transgenic plants. Genetic and physiological analyses demonstrated that SlMYB30 enhances tomato resistance to HVPD stress by boosting the plant's antioxidant capacity and optimizing stomatal morphology. Furthermore, SlMYB30 expression was induced by exogenous salicylic acid (SA), suggesting its involvement in SA signaling or a potential feedback regulatory loop. Under HVPD conditions, tomato plants also showed increased transcription of ISOCHORISMATE SYNTHASE (ICS), a key enzyme involved in SA biosynthesis. Interaction assays revealed that SlMYB30 binds to the MBS motifs within the SlICS promoter, leading to its activation and an increase in SA accumulation, thereby enhancing plant adaptation to HVPD stress. In addition, SlMYB30 positively regulated the expression of the PLASMA MEMBRANE INTRINSIC PROTEIN 1;7 (SlPIP1;7), affecting stomatal morphology and boosting antioxidant enzyme activity. This study elucidates the crucial role that the SlMYB30-mediated SA synthesis pathway plays in conjunction with the aquaporin SlPIP1;7 during HVPD stress, offering molecular targets for breeding crops with enhanced HVPD stress resistance.