Arabinogalactan Proteins in Pollen-Pistil Interactions: Molecular Regulators of Reproductive Barriers and Compatibility.

Arabinogalactan proteins (AGPs) are a family of highly glycosylated proteins that play an important role in the reproductive process of flowering plants. This review summarizes current knowledge of arabinogalactan proteins at various stages of male and female gametophyte development and in the regulation of their interactions-from pollen grain contact with the stigma, through pollen tube (PT) germination and its guided growth toward the embryo sac, to sperm cell delivery to the egg cell. Particular attention is given to the involvement of AGPs in pollen-pistil recognition, pollen tube growth and guidance, self-incompatibility, and reproductive barriers associated with distant hybridization. By integrating recent findings, we highlight the diverse structural and functional roles of AGPs in reproductive processes and discuss current limitations in understanding their molecular mechanisms. The review also identifies key open questions and promising directions for future research on AGP-mediated regulation of reproductive interactions in angiosperms.