Cellular signaling mechanisms during pollen-pistil interactions in brassicaceae

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Flowering plants cannot control the type of pollen grains that land on its stigma and have appropriate recognition mechanisms to either accept or reject the pollen. Successful plant reproduction is dependent on a compatible interaction between the pollen/pollen tube and the pistil. In plant species of Brassicaceae which are characterized by dry stigmas, only a compatible pollen can induce the pistil to provide all the necessary resources for its hydration and penetration into the stigmatic tissue. In contrast, during Brassica (canola, broccoli and cabbage) self-incompatibility (SI) (a selection mechanism to prevent inbreeding), recognition of the self-pollen, induces a highly ordered signaling mechanism that rejects the self-pollen (blocks allocation of pistil resources for pollen hydration/germination). Despite the exciting progress made in understanding plant fertilization, knowledge is still limited about the early signaling mechanisms during pollen/pistil interactions. My long term goal is to gain a thorough understanding of the signaling mechanisms that regulate compatible pollination during plant reproduction and to map the interplay between the compatibility and incompatibility pathways. Through studying self-incompatibility in Brassica, we identified that SI targets the exocytosis-mediated secretory events that are required for compatible pollen acceptance. In a proteomics screen to identify factors regulated by SI, we identified that both phospholipase D-alpha 1 (PLD1) and annexin1 (ANX1) (known regulators of exocytosis) are targeted by SI. The primary focus of this research program is to study the functional role of both PLD1 and ANX1 during compatible pollination events in Brassica and to elucidate the mechanism by which SI targets these proteins. The second aspect is to understand how conserved their functions are in regulating compatible pollination in the model plant Arabidopsis thaliana (a self-fertile species of Brassicaceae), where these proteins are represented by gene families. This research will significantly advance our understanding of early signaling during pollen-pistil interactions, a key event for successful reproduction. Understanding plant reproduction allows us to develop strategies to improve crop yield.