Pollen-pistil interactions in nicotiana
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] To screen for potential mates, angiosperm pistils provide a physical and biochemical barrier that promotes the growth of desirable pollen while preventing growth from undesirable pollen. The pistil controls pollination by secreting molecules that affect pollen tube growth into the extra-cellular matrix (ECM) that pollen tubes grow through. In this work, I investigated pollen-pistil interactions in Nicotiana section Alatae and found two undescribed pollination-based hybridization barriers; a physical size mismatch barrier between species with long pistils and pollen from small flowers, and a molecular rejection mechanism in reciprocal crosses. Several arabinogalactan glycoproteins (AGPs) secreted into the ECM directly affect pollen tube growth. For example, the 120 kDa glycoprotein (120K), required for self-incompatibility associates with vacuole membranes in growing tubes. It is unknown how 120K impacts pollen tube growth, or how it traffics to a vacuole. I identified pollen proteins that bind to 120K, and may function in its trafficking. An E3 ubiquitin ligase, SBP1, and a pollen-specific C2-domain-containing protein (NaPCCP) were identified. Protein interaction domains between 120K and SBP1 or NaPCCP were identified. Furthermore, NaPCCP interacts with phosphatidylinositol 3-phosphate (PI3P). PI3P is associated with endosomes, therefore, NaPCCP may function in an endocytic route of 120K and associated proteins.
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