Regulation of spindle microtubule organization in plants

University Of California-Davis, Davis CA

Investigators

Abstract

Cellular organisms propagate by producing new cells through cell division. When eukaryotic cells divide, they generate the spindle apparatus that ensures the faithful segregation of the genetic material into two daughter cells. This biological machinery is assembled by the cytoskeletal filaments of microtubules. Spindles often have their poles defined by two centrosomes in organisms like fungi and animals. During evolution, however, the centrosome is no longer produced in flowering plants. Yet these spindles lacking this structure can still precisely exercise their essential function in cell division. This research is aimed at understanding the roles of proteins that regulate the formation of the spindle microtubule array in plants. The knowledge learned from spindle assembly in plants also will illuminate how cell division is executed in other organisms. The work will involve the participation of both undergraduate and graduate students. High school students will also have an opportunity to participate in the research during the summers. This project aims to understand mechanisms that regulate acentrosomal spindle microtubule organization in plants by employing two model systems, the basal liverwort Marchantia polymorpha in which the centrosome is present but not always used in mitosis and the flowering plant Arabidopsis thaliana that lacks the structure. Preliminary studies in A. thaliana were focused on the mitotic kinase of Aurora (alphaAur) and its regulator TPXL3, the microtubule nucleator of the gamma-tubulin ring complex (gammaTuRC), and the Kinesin-14 motors of ATK1 and ATK5 that are associated with spindle MTs. When functions of these proteins were compromised, spindles failed to establish convergent poles, and ultimately mutant plants showed severe defects in both vegetative growth and reproduction. The working hypothesis is that alphaAur regulates the functions of gammaTuRC and Kinesin-14 in spindle assembly. Specifically, the formation of mitotic spindles with convergent poles requires Kinesin-14-dependent microtubule organization and poleward accumulation of gammaTuRC. This hypothesis will be tested by employing 1) imaging techniques to determine the actions of essential regulators of spindle microtubule organization during mitosis; 2) genetic tools to dissect functions of targeted proteins; and 3) biochemical methods to learn how their functions are regulated. In vitro and in vivo results garnered from these studies will contribute to elucidating mechanisms that regulate acentrosomal spindle assembly. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.