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.
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:
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, A. A., Kirkpatrick, A., Reeder, S. H., Li, P. and H. A. Owen (2018) Pollen aperture factor INP1 acts late in aperture formation by excluding specific membrane domains from exine deposition. Plant Physiology. Focus Issue on Plant Cell Dynamics. 176: 326-339, http://www.plantphysiol.org/content/176/1/326
Li, P., Ben-Menni Schuler, S., Reeder, S. H., Wang, R., Suarez Santiago, V., and A. A. Dobritsa (2018) INP1 involvement in pollen aperture formation is evolutionarily conserved and may require species-specific partners. J. Exp. Bot. 69: 983-996, https://doi.org/10.1093/jxb/erx407
Albert, B., Ressayre, A., Dillmann, C., Carlson, A., Swanson, R. J., Gouyon, P.-H., and A. A. Dobritsa (2018) Effect of aperture number on pollen germination, survival, and reproductive success in Arabidopsis thaliana. Ann. Bot. 121:733-740, https://doi.org/10.1093/aob/mcx206
Dobritsa, A. A. and S. H. Reeder (2017) Formation of pollen apertures in Arabidopsis requires an interplay between male meiosis, development of INP1-decorated plasma membrane domains, and the callose wall. Plant Signaling & Behavior. e1393136. DOI: http://dx.doi.org/10.1080/15592324.2017.1393136
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