Calcium Dependent Protein Kinases in Pollen Tube Tip Growth

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The long-term goal of this project is to understand the functions of calcium-dependent protein kinases (CPKs) in regulating many aspects of plant growth and development. CPKs (which are defined by a novel structure in which the kinase domain is fused to a calmodulin-like regulatory domain) appear to be unique to plants and certain single-celled organisms, and have not been found in animals. In the model plant Arabidopsis, there are 34 CPKs, 12 of which are expressed in pollen. While many plant CPKs are thought to be involved in regulating the response to environmental stresses, such as drought, heat and cold, recent genetic evidence has been obtained that identifies two of these CPKs as critical to pollen tube tip growth, which is a developmental program. Genetic knockout of CPK17 and 34 results 1) in pollen tubes that are short and slow growing and that are disrupted in their ability to locate and fertilize ovules, and 2) in plants that are essentially sterile. The ability to restore normal fertility by transferring CPK34 genes into these plants provides an unprecedented opportunity to determine the features of a CPK that are important for their functions. A key hypothesis guiding the research is that specific functions of CPK17 and 34 are encoded in the kinase domain. The aims of this project include 1) defining the molecular pathways by which these CPKs promote pollen tube tip growth and tropism, 2) delineating the cellular processes regulated by these CPKs, starting with endocytosis and exocytosis at the tip of a growing pollen tube, and 3) identifying how these CPKs regulate vesicle trafficking and cytoskeletal dynamics, which are critical processes in polarized pollen tip growth. This research will provide new insights into how calcium signals are coded and decoded in plant systems. Broader impacts. The research will have additional impacts that derive from educational and mentoring contributions. The Harper lab is actively engaged in mentoring research activities at all academic levels, from early career assistant professors to undergraduates. The planned research will provide training for both undergraduate and graduate student in the area of molecular biology, confocal microscopy, genetics and proteomics. Project results will be communicated to the public through publications, data base contributions, scientific seminars, and lectures to undergraduates and K-12 students.