PbMYB57 positively mediates glucose-responsive lignification in pear

Stone cell lignin deposition is a key determinant of pear fruit texture, with its dynamic accumulation tightly linked to sugar status during development. While the conserved energy sensor SnRK1 mediates cellular sugar signaling, its downstream regulatory mechanism in fruit lignin biosynthesis remains largely unknown. Here, we demonstrate that PbSnRK1 modulates pear lignin biosynthesis in a glucose concentration-dependent manner, strongly promoting lignin accumulation under low-glucose conditions and reducing it under high-glucose conditions. Using transcriptomic profiling of PbSnRK1-overexpressing calli, we identified the glucose-responsive R2R3-MYB transcription factor PbMYB57 as a key downstream component. Functional assays across glucose concentrations revealed that PbMYB57 promotes lignin biosynthesis specifically under low-glucose conditions, consistent with the glucose-dependent functional specificity of PbSnRK1 in the positive regulation of lignification. PbMYB57 directly binds the AC cis-element in the promoter of PbC4H1 to activate its transcription. Genetic epistasis assays verify that PbMYB57 acts genetically downstream of PbSnRK1 and largely mediates the PbSnRK1-driven accumulation of lignin under low-glucose conditions. These findings define PbMYB57 as a critical mediator of glucose-responsive stone cell lignification, providing new insights into sugar-regulated secondary metabolism and genetic targets for pear quality improvement.