Mark Johnson, Brown University, Molecular Dialogues Between Pollen and Pistil

Alexander R. Leydon and Mark A. Johnson

Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI USA

Pollen tubes penetrate the stigma, extend through specialized transmitting tissue, are attracted to ovules, and deliver two sperm to the female gametophyte so one can fuse with the egg to form the embryo and the other with the central cell to form endosperm. This double fertilization process depends on a system of positive and negative cell:cell interactions that optimize fertility for flowering plants. We have defined changes in pollen tube gene expression that orchestrate crucial cellular interactions as the pollen tube grows through the pistil by defining a group of MYB transcription factors that are required for this response. Pollen tubes lacking these three transcription factors are not recognized by the female gametophyte when they arrive inside an ovule; they fail to induce changes in female gametophyte cells and continue growing within the female gametophyte without releasing their cargo of sperm cells. In many respects, pollen tube mutants lacking these MYB transcription factors behave like pollen from a different species – there is a breakdown in cellular recognition required for fertilization. Our goal is to define the critical effector proteins mediating recognition between pollen tube and the female gametophyte. We have made progress via RNA-sequencing of inter-ecotypic cross-pollinations to precisely define patterns of pollen and pistil gene expression during growth of wild type and mutant pollen tubes. We've also been able to define a subset of MYB-regulated secreted peptides that are sufficient to restore proper identity to mutant pollen tubes. Our goal is to understand the biochemical function of these peptides that mediate cellular interactions between the gametophytes.