Brassinosteroid signaling promotes stone cell lignification by enhancing nuclear accumulation of PbrBEH3 in pear fruit

Stone cells, characterized by heavily lignified secondary cell walls, severely impair the texture and eating quality of pear fruit, particularly in Asian cultivars. Although brassinosteroids (BRs) are key hormones regulating fruit development, their role in stone cell formation has remained unclear. Here, we found that exogenous BR treatment promotes stone cell lignification in pear fruit. Using co-expression network analysis across 24 diverse tissues and correlation analysis of 206 pear accessions, we identified PbrBEH3, a member of the BRASSINAZOLE-RESISTANT (BZR)/BRI1-EMS-SUPPRESSOR (BES) transcription factor family, the expression was strongly and positively correlated with stone cell content. Functional analyses demonstrated that transient overexpression (OE) of PbrBEH3 in pear fruit and stable OE in pear callus significantly increased lignin accumulation, whereas CRISPR/Cas9-mediated knockout reduced lignin levels. Consistently, PbrBEH3 OE in Arabidopsis thaliana promoted lignin deposition in stems. Mechanistically, BR treatment enhanced nuclear accumulation of PbrBEH3, which directly activated Pbr4CL1 and PbrMYB169 transcription by binding to E-box and BRRE cis-elements in their promoters, respectively. Collectively, our findings establish PbrBEH3 as a crucial transcriptional activator that integrates BR signaling to regulate lignin biosynthesis and stone cell formation in pear fruit. This work provides novel insights into the hormonal regulation of fruit quality and identifies a potential molecular target for improving fruit texture in pear breeding.