The transcription factor SlLBD40 regulates seed germination by inhibiting cell wall remodeling enzymes during endosperm weakening

Uniform seed germination is crucial for consistent seedling emergence and efficient seedling production. In this study, we identified a seed-expressed protein in tomato (Solanum lycopersicum), lateral organ boundaries domain 40 (SlLBD40), that regulates germination speed. CRISPR/Cas9-generated SlLBD40 knockout mutants exhibited faster germination due to enhanced seed imbibition, independent of the seed coat. The expression of SlLBD40 was induced during the imbibition process, particularly in the micropylar endosperm, suggesting its role in endosperm weakening. Gene ontology analysis of RNA-seq data indicated that differentially expressed genes were enriched in cell wall-related processes. SlLBD40 directly targeted genes encoding cell wall remodeling enzymes implicated in endosperm weakening, including expansin 6 (SlEXP6), xyloglucan endotransglucosylase/hydrolase 23 (SlXTH23), and endo-β-mannanase 1 (SlMAN1). Our findings shed light on the role of endosperm weakening in regulating seed germination and propose potential gene targets for improving germination in species constrained by endosperm strength.