Involved in cell specification during anther development. Required for the differentiation of primary parietal cells into secondary parietal cells in anthers (PubMed:22913653). May serve as an extracellular ligand for the MSP1 receptor kinase to limit sporocyte number in ovules (PubMed:18248596). Interacts with MSP1. Expressed in roots, and anthers and ovules during meiosis. Male-sterile phenotype due to the absence of tapetal cells in the developing anthers.