Coordination of lignin and pectin remodeling by a NAC transcription factor regulates seed abscission in sesame (Sesamum indicum L.)

Seed shattering, which facilitates seed dispersal, is essential for plant reproduction but causes substantial yield loss in sesame (Sesamum indicum L.). It occurs through capsule dehiscence and/or seed abscission from the placenta, either simultaneously or independently depending on the species. In this study, we investigated cell wall-associated factors underlying delayed seed abscission in the sesame cultivar Suwon195 (SW195) relative to the easy-shattering cultivar IT030100. Histological and transcriptome analyses indicated that cell wall remodeling, particularly involving pectin and lignin, contributes to the delayed abscission phenotype of SW195. SW195 showed higher pectin methylesterase activity and stronger accumulation of low-methyl-esterified homogalacturonan, together with lower polygalacturonase-associated pectin turnover, than IT030100. These changes are consistent with a pectin-remodeling state that favors wall stabilization in the SW195 abscission zone (AZ). AZ lignification was also weaker in SW195. Pharmacological inhibition of lignin biosynthesis altered pectin staining and reduced seed abscission in IT030100, whereas monolignol supplementation restored both phenotypes, supporting a functional association between lignification, pectin-related wall remodeling, and abscission. QTL mapping and whole-genome resequencing identified a major locus on chromosome 9 encompassing a NAC transcription factor (SiNAC; SIN_1025412) and a pectin methylesterase inhibitor (SiPMEI; SIN_1025380). Transient overexpression of SiNAC enhanced lignin biosynthesis in sesame. Together, these findings indicate that coordinated lignin deposition and pectin remodeling are associated with seed abscission in sesame and identify candidate genetic components for breeding reduced-shattering cultivars.