Chloroplasts are organelles that convert light energy to chemical energy through photosynthesis. The movement of chloroplasts within the cell for the optimization of light absorption is crucial for plant survival. Cellular motor proteins and cytoskeletal tracks can facilitate transport of organelles. As an ancient superfamily of microtubule-dependent motors, kinesins participate in various cellular activities including cytokinesis, vesicle and organelle movements. Based on phylogenetic relationships and functional analysis, the kinesin superfamily has been subdivided into more than 14 families, most of which can be found in plants. With the ever increasing amount of genomic information, it is important and beneficial to systematically characterize and document kinesins within an organism. As a result of my collaborative work with other members of the Vidali lab, a detailed phylogenetic characterization of the 76 kinesins of the kinesin superfamily in the moss Physcomitrella patens is reported here. We found a remarkable conservation of families and subfamily classes with Arabidopsis, which is important for future comparative analyses of functions. Some of the families are composed of fewer members, while other families are greatly expanded in moss. To improve the comparison between species, and to simplify communication between research groups, we proposed a classification of subfamilies based on our phylogenetic analysis. As part of my efforts in studying chloroplasts motility, I investigated the function of two members of Physcomitrella kinesin family 14 class V proteins, Ppkin14-Va and -Vb. These two proteins are orthologs of the Arabidopsis KAC proteins which mediate actin-based chloroplast movement in Arabidopsis thaliana. In contrast, in the Physcomitrella both actin filaments (AFs) and microtubules (MTs) participate in chloroplast movement. Our results show that Ppkin14-Vs are important for maintaining chloroplast dispersion. They also function during chloroplast light avoidance responses via an AF-dependent, rather than MT-dependent mechanism. Although two Ppkin14- Vs do not act as MT-based motors, our phylogenetic study on moss kinesins provides an important source of information to track other potential kinesins that are predicted to move chloroplasts on MTs.
Worcester Polytechnic Institute
Biology & Biotechnology
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Shen, Zhiyuan, "Phylogenetic Characterization of the Kinesin Superfamily and Functional Analysis of PpKin14-Vs in Physcomitrella patens" (2014). Masters Theses (All Theses, All Years). 1158.
gene knockout, phylogenetic analysis, kinesin, microtubule, intracellular motility, PpKinesin14-Vs, chloroplast photorelocation, moss