Endosperm secretion remodels the maternal seed coat

Arabidopsis thaliana endosperm directly secretes cell-wall-loosening proteins that enable maternal seed-coat cell elongation, with three expansins necessary and sufficient for seed growth.

• Why it matters: Maternal tissues must expand to enclose developing offspring, but it was unclear whether endosperm signals directly drive maternal cell wall loosening and elongation.
• What they did: The study shows the HAIKU-WRKY10 pathway activates an endosperm secretory program enriched in cell-wall-associated proteins that spread across inner seed-coat layers via a shared extracellular domain.
• The result: Paternal DNA methylation and maternal Polycomb activity jointly regulate this secretory/expansin program, and Polycomb is required for timely shutdown of expansin expression.