Intercellular Signaling in Pollen Tube Reception

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How do cells sense and establish communication with other cells in order to allow for beneficial or compatible interactions as opposed to harmful interactions? Plant pollination is an excellent system for gaining insight into this question because intercellular communication between male and female tissues is critical for the recognition of compatible pollen. In plants a pollen tube (PT) grows from a pollen grain that has landed on the surface of a flower's female reproductive tissue. The tube extends through that tissue towards the egg-containing ovary. Upon entering the ovary the tube stops growing and bursts open, releasing sperm that fertilize an egg, which in turn develops into a seed. In order to deliver the sperm cells to the ovary, the PT must sense that it has arrived at the right place and change from tip-growth to explosive release of the sperm it contains. This project seeks to determine the molecular signals that communicate to a PT that it has entered the ovary and must stop growing and release its sperm. Female gametophytic mutations in FERONIA (FER), a receptor-like kinase, and NORTIA (NTA), a member of the MILDEW RESISTANCE LOCUS O (MLO) family of 7-transmembrane proteins, cause PTs to continue growing inside of the receptive synergid instead of rupturing to release the sperm, indicating that these genes form part of a signaling network. This project is aimed at further elucidation of the molecular mechanisms used for communication between the synergid and PT during PT reception, using NTA as the anchor molecule. Synergids are highly specialized cells whose sole function is to communicate with PTs. Experiments will be performed to define the cell biology of the synergid cells before, during and after PT reception and to determine which domains are necessary for NTA localization and function and to determine how NTA fits into the dynamic cellular changes that occur during PT reception. The second goal of the project is to identify new members of the PT reception pathway and determine how they act in the signaling pathway. Enhancer and suppressor mutants of the gene nta will be characterized for roles in PT reception and NTA will be used as bait in yeast-2-hybrid screens to identify other members of the pathway. The results of this project will provide a clearer picture of the signaling pathway involved in PT reception and may also be transformative in our understanding of how self/non-self recognition takes place. A graduate student, post-doc, and undergraduate student will be trained in the fields of plant genetics and cell biology during this project. Students in a cell biology lab taught by the Principal Investigator will investigate proteins that are predicted to be involved in PT reception in an inquiry-based lab module and an outreach program will be conducted to encourage rural Oklahoma high schools to incorporate plant science research in their curricula.