Microtubule Organization by Kinesin-12 in the Phragmoplast

University Of California-Davis, Davis CA

Investigators

Abstract

Intellectual merits. This project is devoted to understanding cell division mechanisms in plants. Plant cells divide by laying down a physical barrier called the cell plate between two daughter nuclei. In order to achieve this goal, organisms of advanced green algae and land plants have developed a common cytokinetic apparatus named the phragmoplast which is a key evolutionary landmark. The phragmoplast is established by a framework of the cytoskeletal element of microtubules, which are aligned perpendicularly to the future cell plate. Microtubules are dynamic polar filaments with their plus ends exhibiting more rapid growth capability than their minus ends. Phragmoplast microtubules are organized into a bipolar array with their plus ends located at or near the division site. Vesicles generated by the Golgi apparatus are transported toward microtubule plus ends, resulting in the assembly of the cell plate. How microtubules are organized into this highly ordered form is the central question being addressed in this project for the next three years. A number of studies suggest that microtubule-associated proteins and the microtubule-based motor kinesins are critical players for microtubule organization in the phragmoplast. We have been using the cress plant Arabidopsis thaliana as a model for our studies, and have discovered that three Kinesin-12 members of the kinesin superfamily exclusively appear at microtubule plus ends in the developing phragmoplast, and play a critical role in microtubule organization. The planned studies are aimed at testing the hypothesis that the Kinesin-12 motors and their binding proteins form a motor complex to regulate the bipolar organization of phragmoplast microtubules. In order to test this hypothesis, the first objective is to apply genetic approaches to dissect how the three Kinesin-12 motors work together in the phragmoplast. The second objective is to understand functions of two Kinesin-12-binding proteins by using biochemical, cell biological, and genetic tools. The last objective focuses on understanding how the function of Kinesin-12 is linked to that of the microtubule-associated protein MAP65-3. Discoveries to be made are going to provide a protein-protein interactive picture at microtubule plus ends in the phragmoplast. Broader impacts. In this project, the use of the model organism Arabidopsis thaliana will bring insights into molecular mechanisms that are responsible for the invention of the phragmoplast during the evolution toward land plants. Experimental results will be made public by journal publications. They will also be translated into lecture materials to reach 250+ undergraduate students in a Cell Biology class taught each year by the Principal Investigator of this project. In the meantime, the participating graduate student receives interdisciplinary training in areas of biochemistry, cell biology and genetics. In addition, the project engages high school students and undergraduate students by providing them with hands-on research experience in the laboratory. By directly contributing to discoveries, these students share the excitement that could inspire them to pursue a career in science.