Research Activity: Tip growth is a form of plant cell growth that although restricted to a few cell types, is essential for the development of plant species ranging from algae to flowering plants. In seed plants in particular, the tip-growing pollen tube is required for fertilization and thus propagation of the species. The root hair is important for absorption of water and minerals required for growth and development of the entire plant. This project will focus on deciphering the molecular signals that control tip growth, thus impacting an evolutionarily wide range of plant cell development. The research will be carried out in an emerging plant model system, the moss Physcomitrella patens. The ease of molecular genetic manipulation and the abundance of tip growing cells make moss ideal for these studies. The moss system is unique among plants for its gene-targeting capabilities. Additionally Dr. Bezanilla recently developed a rapid RNA interference assay, which rapidly reveals plant gene function and is unparalleled in any plant system. Using this assay, Dr. Bezanilla found that certain proteins participating in the actin cytoskeletal network are critical for tip growth. These studies have lead to a working model whereby growth polarization is controlled by a molecular signaling cascade stemming from activation of the plant-specific small GTPase ROP, which in turn signals to the actin monomer binding protein profilin via formins, cellular nucleators of actin filaments, thus coordinating actin dynamics to occur at the site of growth. The project will test this model using a combination of reverse genetics, dynamic live-cell imaging, and molecular interaction screens. Three major questions will be addressed: (1) How is ROP regulated? (2) Do formins function in the ROP-profilin pathway? and (3) What is the molecular composition of the ROP-profilin pathway? Many organisms, including fungi and animals, control cellular morphogenesis via a similar signaling cascade. Thus this research will provide novel comparative insights into this evolutionarily conserved process.
Broader Impacts: This project has potential agricultural benefits for society. By elucidating the fundamental mechanisms controlling plant cell tip growth, this research will impact the understanding of important plant cell types, which are involved in determining overall plant fitness and thus crop yields. The project will also integrate research with teaching and training and will broaden the participation of underrepresented groups in science. Dr. Bezanilla, herself a member of an underrepresented minority in science, has recruited and mentored an excellent minority postdoctoral researcher. Dr. Bezanilla will also develop a course on moss methods that will be taught both at the University of Massachusetts as well as at partner minority serving institutions through an NSF-funded Northeast Alliance for Graduate Education and the Professoriate to further enhance recruitment of underrepresented groups in science.
In the last half century, we have gained deep insights into how cells work. However, how cells obtain their final shape within an organism is still an open question. Research funded by this award has begun to address this fundamental question. Plant cells are an excellent system to study cell shape, as they are surrounded by a semi-rigid wall, but at the same time can obtain a variety of different shapes. Since the raw materials for the cell wall are synthesized inside the cell, it is evident that intracellular events play a critical role in dictating how this semi-rigid encasment is patterned. The research funded by this award took advantage of a simple plant, a moss, in which there are few cell types, but importantly this moss is amenable to precise genetic manipulations. This allows the researchers to remove an exact number of proteins from the organism and ask the quesiton: how does loss of this protein affect the ability of the organism to pattern its cells? Using this approach the studies from this award produced 15 peer-reviewed publications reporting novel insights into how plants pattern their cells. The researchers have developed a model that continues to drive this research forward. They have found that proteins within the cell that can self-assemble into long polymers must be rapidly turned over in order to generate the elongated cells of the young moss plants under investigation. The self assembling polymers are incredibly dynamic. The research has developed tools that enable analysis of microscopy images to accurately quantify how slow or fast the polymers turn over in live cells. These tools are generally applicable for quantification of any set of rapidly changing images. Additionally the researchers have developed innovative courses for undergraduates that incorporate aspects of their research in the class room. Students learn to work with moss and even learn to carry out precise genetic manipulations leading to expression of fluorescently labelled proteins. Students can then analyze where the fluorescent proteins are localized and use these studies to learn about fundamental cell biological principles. Moss is an emerging new cell biological system and the research from this award has helped to propel this model system forward. Importantly, investigators from many univeristies in the Northeast have come to the research facility at UMass Amherst to learn how to work with moss. A number of exciting new collaborations have emerged as a result of this funding.
