Cellular signalling mechanisms during pollen-pistil interactions in Brassicaceae

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Plants maintain their yield, vigour and genetic diversity through appropriate selection of genetically diverse mates while rejecting related partners. In most flowering plants, successful reproduction is controlled at the earliest stages of pollination when the pollen interacts with the stigmatic papillary cell of the female. Following a favourable (compatible) interaction between the pollen and the stigma, the pollen tube grows through the style and fertilizes the ovule. In contrast, to avoid genetically similar mates (self-pollen), plants utilize self-incompatibility (SI) system as a genetic barrier to prevent self-pollen from developing on the stigma, allowing development of only cross-pollen, thereby promoting hybrid vigour and diversity. During SI response in Brassica, interaction between the pollen (male) ligand SCR/SP11 and the stigma (female) SRK (receptor kinase), leads to recruitment of ARC1 E3 ligase to the proteasome, where ARC1 facilitates degradation of various downstream compatibility factors. We have characterized at least three of these downstream targets and their role in pollination. My long-term goal is to gain a thorough understanding of the signaling mechanisms that regulate compatible and incompatible pollination events during plant reproduction. Three specific research objectives are described. 1) Our preliminary evidence suggests that MAPKs (mitogen-activate protein kinases) are constitutively activated in the stigmas and are required for mediating compatible pollination. We propose to identify the upstream regulators of MAPKs that are involved in mediating compatible pollination. Identification of the activator(s) of these MAPKs would allow us to build the compatible signaling pathway 2) Elucidate the signaling mechanism behind activation of Exo70A1 during pollination. The role of MAPKs in influencing the function of Exo70A1 through phosphorylation will be assessed. This objective will lead to completion of the pathway downstream of MAPKs that is required for compatible interactions 3) Characterizing JDP1 (J-domain protein) as a positive regulator of SI. Although a number of targets of ARC1 have been identified, no other positive regulator of SI pathway has been identified after ARC1. JDP1 can interact with ARC1 and suppression of JDP1 leads to breakdown of SI, suggesting JDP1 is a positive regulator of SI. We propose to use transgenic, molecular and biochemical approaches to elucidate how JDP1 participates in SI signaling. Given that crop-yield in most of our staple foods impinge on successful reproduction, understanding the genetic networks that drive the reproductive potential of a crop plant is crucial for our global move toward sustainability. Our research program aims to address this from both a discovery and an applied perspective. The HQPs trained through this program will have a unique advantage of finding jobs in the canola industry and will have opportunities in academia, industry and the government.