Pollen Tube Reception

How do cells sense and establish communication with other cells in order to allow beneficial invasions and prevent harmful invasions?

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, the guidance of tip-growing pollen tubes (PTs) to the ovules, and finally, the entry of the PT into the female gametophyte and release of the sperm cells so that double fertilization can occur to produce viable seeds. In order to deliver the sperm cells to the female gametes, the PT must sense that it has arrived at the right place and change its growth pattern from tip-growth to explosive growth as it “invades” a synergid cell. 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 the 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.  

Aim 1 is to determine the role of the MLO-family protein, NTA, in the PT reception signaling machinery. 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.

Aim 2 is to identify new members of the PT reception pathway and determine how they act in the signaling pathway. nta enhancer and suppressor mutants 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. With this project, we expect to be able to provide a clearer picture of the signaling pathway involved in PT reception and ultimate release of sperm so that double fertilization can occur.

Funded by the National Science Foundation grant number 1457098.

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Pollen tube reception mutants have problems in male-female communication when the pollen tube arrives at the synergid cells of the female gametophyte.  This results in a polen tube overgrowth phenotype where the pollen tube doesn't burst to release the sperms cells. As a result, ovules remain unfertilized and viable seeds are not produced.

NTA-GFP localizes in Golgi-associated compartments and is excluded from the filiform apparatus before pollen tube reception. Jones, et al., 2017

NTA-GFP accumulates at the filiform apparatus when the pollen tube makes contact with the synergid cell.  The receptor-like kinase FERONIA is necessary for this redistribution.