Abstract
In flowering plants, immotile sperm cells develop within the pollen grain and are delivered to female gametes by a pollen tube. Upon arrival at the female gametophyte, the pollen tube stops growing and releases sperm cells for successful fertilization. Several female signaling components essential for pollen tube reception have been identified; however, male components remain unknown. We show that the expression of three closely related MYB transcription factors is induced in pollen tubes by growth in the pistil. Pollen tubes lacking these three transcriptional regulators fail to stop growing in synergids, specialized cells flanking the egg cell that attract pollen tubes and degenerate upon pollen tube arrival. myb triple-mutant pollen tubes also fail to release their sperm cargo. We define a suite of pollen tube-expressed genes regulated by these critical MYBs and identify transporters, carbohydrate-active enzymes, and small peptides as candidate molecular mediators of pollen tube-female interactions necessary for flowering plant reproduction. Our data indicate that de novo transcription in the pollen tube nucleus during growth in the pistil leads to pollen tube differentiation required for release of sperm cells.