“Love Is Strong, and You're so Sweet”: JAGGER Is Essential for Persistent Synergid Degeneration and Polytubey Block in Arabidopsis thaliana

Successful double fertilization and subsequent seed development in flowering plants requires the delivery of two sperm cells, transported by a pollen tube, into the embryo sac of an ovule. The embryo sac cells tightly control synergid cell death, and as a result the polyspermy block. Arabinogalactan proteins are highly glycosylated proteins thought to be involved in several steps of the reproductive process. We show that JAGGER, Arabinogalactan Protein 4, is an important molecule necessary to prevent the growth of multiple pollen tubes into one embryo sac in Arabidopsis thaliana. In jagger, an AGP4 knockout mutant, the pistils show impaired pollen tube blockage as a consequence of the survival of the persistent synergid. JAGGER seems to be involved in the signaling pathway that leads to a blockage of pollen tube attraction. Our results shed light on the mechanism responsible for preventing polyspermy in Arabidopsis and for safeguarding successful fertilization of all ovules in one pistil, ensuring seed set and the next generation. The precise delivery of a pair of sperm cells inside the embryo sac of an ovule in Arabidopsis is fundamental to guarantee successful fertilization. We show that JAGGER, Arabinogalactan Protein 4, is essential for this step of plant reproduction in Arabidopsis. jagger ovules fail to undergo persistent synergid cell death, leading to the attraction of an extra pollen tube into one embryo sac. Moreover, we show that JAGGER is acting from the sporophytic tissues near the ovule to prevent polytubey and thus polyspermy.