The EjbZIP11–EjWRKY41 module regulates lignin accumulation in russeted loquat fruit by activating lignin biosynthetic genes

Fruit russeting is a preharvest physiological disorder that severely affects the fruit quality and marketability of loquat (Eriobotrya japonica Lindl.). Although russeting has been widely documented in apple and pear, the key regulators and cooperative mechanisms underlying russet formation in loquat remain unknown. Here, we show that lignin accumulates markedly in russeted tissues, concomitant with enhanced expression of lignin biosynthesis–related genes. By integrating transcriptomic and metabolomic profiling with weighted gene co-expression network analysis (WGCNA), we identified two hub transcription factors (TFs), EjbZIP11 and EjWRKY41, that are closely associated with lignin accumulation. Functional analyses demonstrated that both EjbZIP11 and EjWRKY41 promote lignin deposition. Yeast one-hybrid (Y1H), electrophoretic mobility shift (EMSA), and dual-luciferase (dual-LUC) assays revealed that EjbZIP11 directly binds to and activates the promoters of Ej4CL9, EjPRX4, and EjPRX10, whereas EjWRKY41 directly targets the promoters of Ej4CL9 and EjCCoAOMT3; co-expression of the two TFs further strengthened transcriptional activation of lignin pathway genes. Moreover, yeast two-hybrid (Y2H), split-luciferase (split-LUC) complementation, bimolecular fluorescence complementation (BiFC), and pull-down assays confirmed that EjbZIP11 and EjWRKY41 physically interact both in vivo and in vitro. Notably, each TF also directly binds to and activates the other’s promoter, establishing a reciprocal transcriptional regulatory relationship. Collectively, our study identifies an EjbZIP11–EjWRKY41 regulatory module that promotes lignin accumulation through protein–protein interaction and bidirectional transcriptional regulation, providing candidate targets for genetic improvement of russeting resistance in loquat.