Cells rely on a regulated production of extracellular materials to control their shapes, growth, and motility, to promote tissue formation, and to protect themselves. Despite the importance of extracellular structures in development and disease, the question of how cells decide when, where, and in which manner these materials should be produced and deposited is far from being understood in any system. My laboratory studies formation of complex extracellular structures using development of exine, the outer cell wall of plant pollen grains, as a model.
Exine, the amazing cell wall of pollen grains:
Fig. 1 Pollen exine assembles into elaborate species-specific patterns.
Pollen grains of six plant species are shown.
Having evolved as a protector of male reproductive units, a pollinator-interacting entity, and a site of pollen-pistil recognition, exine is important for plant reproduction and speciation. Understanding the mechanism of its development could enable improved manipulations of plant reproduction by controlling pollination. In addition to this, exine formation is a fascinating system that lies at the intersection of many disciplines, ranging from cell and developmental biology to biochemistry, evolutionary biology, materials science, and molecular engineering. The following features make exine an exciting system to study:
Exine has a very unique composition, different from other plant cell walls. It is made of sporopollenin, a biopolymer unparalleled for its strength, elasticity, and chemical durability. Sporopollenin’s chemical structure and the genetic and biochemical networks that control its production are poorly understood. Because of this biopolymer’s remarkable material properties, understanding the processes responsible for sporopollenin synthesis is of interest not only to plant biologists, but also to materials scientists.
Exine contains species-specific adhesives that participate in strong and selective binding between male pollen and receptive female stigma cells and are possibly involved in speciation. The identity of adhesives is unknown, but their chemical and physical properties suggest that they are unlikely to be proteins, implying that exine mediates a very unusual type of cell-cell recognition.Understanding the nature of these adhesives may result in the creation of strong and specific glues.
Exine has an enormous morphological diversity across taxa and assembles into thousands of intricate species-specific 3D patterns (Fig. 1). How exine materials are assembled on pollen surfaces with such a precision into dramatically diverse patterns are the intriguing evo-devo and cell-biological questions.
Research goals and approaches
We are trying to learn how sporopollenin is synthesized, exine is developed, exine patterns are laid out, and eventually would like to understand how the forms of these complex structures determine their functions. To answer these questions, we utilize genetics, molecular biology, confocal and electron microscopy, and biochemistry. We have a large collection of Arabidopsis exine mutants (Fig. 2) that help us to identify and study molecular players and events involved in sporopollenin biosynthesis and exine formation. In the future, these data from a model plant will be used as a foundation for evo-devo studies regarding the generation of the enormous variety of exine patterns observed in nature.
Fig. 2 Examples of phenotypes of our exine mutants.
Wild-type pollen grains are in the top left panel.
Dobritsa lab – May 2016:
Byungha Lee, Rui Wang, Ronnie Fox, Holly Welfley, Galen Rask
Anna Dobritsa, Sarah Reeder, Michelle Tan, and Prativa Amom
- Dr. Byungha Lee (2014 -)
- Dr. Rui Wang (2016 -)
- Dr. Peng Li, Tsinghua University, China (2015-2016)
- Samira Ben-Menni Schuler, University of Granada, Spain (2015)
- Sarah Reeder, Research Associate (Sept. 2013 - )
Ronnie Fox, OSU Molecular Genetics, NSF fellowship from Pollen Research Coordination Network and ASPB SURF (2014 -)
Holly Welfley, OSU Molecular Genetics (2014-)
Zach Weber, OSU Molecular Genetics (2014-)
Prativa Amom, OSU Molecular Genetics (2015-)
Michelle Tan, OSU Molecular Genetics (2015-)
Sydney Bernthold – K12, Metro School Internship, Metro High School (March-May 2016)
Kevin Freeman – K12, Metro Capstone Program, Metro High School (February – May 2014)
OSU – Columbus School District Young Scholars Program, K12, Biology Workshop (Spring 2014)
Reeder, S. H., Lee, B. H., Fox, R., and A. A. Dobritsa (2016) A ploidy-sensitive mechanism regulates formation of apertures on the Arabidopsis pollen surface and guides localization of the aperture factor INP1. PLOS Genetics 12: e1006060 DOI:10.1371/journal.pgen.1006060
Prieu, C., Matamoro-Vidal, A., Raquin, C., Dobritsa, A., Mercier, R., Gouyon, P.-H., and B. Albert (2016) Aperture number influences pollen survival in Arabidopsis mutants. Am. J. Bot. (Special Issue on the Ecology and Evolution of Pollen Performance) 103:432-439, 10.3732/ajb.1500301.
Dobritsa, A. A. and D. Coerper (2012) The novel plant protein INAPERTURATE POLLEN1 marks distinct cellular domains and controls formation of apertures in the Arabidopsis pollen exine. Plant Cell 24: 4452-4464.
Dobritsa, A. A., Geanconteri, A., Shrestha, J., Carlson, A., Kooyers, N., Coerper, D., Urbanczyk-Wochniak, E., Bench, B. J., Sumner, L. W., Swanson, R., and D. Preuss (2011) A large-scale genetic screen in Arabidopsis to identify genes involved in pollen exine production. Plant Physiology 157: 947-970.
Dobritsa, A. A., Lei, Z., Nishikawa, S., Urbanczyk-Wochniak, E., Huhman, D. V., Preuss, D., and Sumner, L.W. (2010) LAP5 and LAP6 encode anther-specific proteins with similarity to chalcone synthase essential for pollen development in Arabidopsis thaliana. Plant Physiology 153: 937-955.
Dobritsa, A. A., Nishikawa, S., Preuss, D., Urbanczyk-Wochniak, E., Sumner, L. W., Hammond, A., Carlson, A.L., and Swanson, R. J. (2009) LAP3, a novel plant protein required for pollen development, is essential for pollen exine formation. Sex. Plant Reprod. 22: 167-177.
Dobritsa, A. A., Shrestha, J., Morant, M., Pinot, F., Matsuno, M., Swanson, R., Møller, B. L., and D. Preuss (2009) CYP704B1 is a long-chain fatty acid w-hydroxylase essential for sporopollenin synthesis in pollen of Arabidopsis thaliana. Plant Physiology 151: 574-589.