Pollen apertures as a model for formation of distinct extracellular domains

Ohio State University, The, Columbus OH

Investigators

Abstract

In an organism, deposition of extracellular materials next to a cell can protect the cell, change its growth and morphology, or help it to move and communicate with other cells. To be able to perform such important functions, extracellular materials must be deposited very precisely, but how cells achieve such precision is mostly unknown. A beautiful example of an extracellular structure with a very precise deposition is the wall surrounding plant pollen. Pollen grains from different species often look remarkably different, in part, because wall materials are deposited at some places on pollen surface and absent from the others. The places where pollen wall is absent are called apertures, and these structures help pollen perform its reproductive function. Across species, pollen apertures often differ in shape, number, and positions, but within a species aperture patterns are usually the same. Using formation of pollen apertures as a model, this project will investigate how cells determine which surface areas will lack extracellular structures and how positions of such areas are marked. Understanding pattern formation in the context of pollen will provide insight into pattern formation during many developmental processes. In broader impacts of this project, several young scientists will be trained and the results of the work will be communicated to larger audiences through lectures in an Arts & Science undergraduate course, microscopy courses, and by interacting with middle- and high-school students during biology enhancement workshops and a Capstone internship program. How cells develop precisely defined domains of extracellular structures is an important and poorly understood question. Pollen grains provide an excellent model for studying this problem, as their surfaces are covered by the cell wall, exine, which assembles into diverse species-specific patterns. This wall protects sperm cells within the pollen grains and plays several other important roles in plant reproduction. In addition to the exine-covered areas, pollen surfaces of most plant species have characteristic openings, or apertures, where exine is absent or reduced. This indicates that, in the course of pollen development, specific domains are formed on pollen surface, which are reliably recognized by the cell wall deposition machinery as different from the rest of the surface and which will become apertures. As is the case with exine patterns, apertures often vary greatly across species, differing in their number, positions, and morphology, yet within each species their patterns are under tight developmental control. As well-defined, tightly regulated, and easily recognizable and quantifiable structures, apertures provide an attractive handle for addressing the complex problems of pollen surface pattern formation and can serve as a powerful model for generation of distinct extracellular domains, a process important in a wide variety of cells and organisms. Through a variety of genetic, cell-biological, and computational methods and using Arabidopsis pollen as a model, this project aims to discern how the aperture-specifying domains are formed and to define cell-biological events important for aperture development. This will allow creating a paradigm for how plant cells generate functionally distinct peripheral domains, and how cell wall deposition machinery interprets these domains to generate extracellular differences.