A β-Mannanase Gene, MAN2, Coordinates Tomato Fruit and Seed Development and Salt Stress Tolerance

Tomato (Solanum lycopersicum) β-mannanase is known as playing an important role in mannan degradation; however, its biological functions and transcriptional regulation remain poorly understood. Here, we characterized the roles of mannan-1,4-β-mannanase 2 (SlMAN2) in tomato development and salt stress tolerance. Results showed that SlMAN2 was preferentially expressed in seeds, stems, stamens, and stigmas. SlMAN2 overexpression significantly increased fruit and seed size, accelerated seed germination, and enhanced salt tolerance under 100 mM NaCl, whereas knockout mutants exhibited the opposite phenotypes. Notably, dual-luciferase assays and electrophoretic mobility shift assay (EMSA) demonstrated that the transcription factor SlDOF3.1 directly binds to the SlMAN2 promoter and activates its transcription, but SlMAN2 overexpression suppressed SlDOF3.1 expression, suggesting the existence of a negative feedback regulatory loop. Collectively, our findings reveal that SlMAN2 functions as a pleiotropic regulator coordinating tomato fruit and seed development with salt stress tolerance and uncover a SlDOF3.1–SlMAN2 regulatory module underlying these processes.