Intellectual merit. The chloroplast is an important cellular compartment in higher plants and in some algae it is the site of oxygen-producing photosynthesis, which supports life of most organisms on earth. Chloroplasts are not generated spontaneously; instead they arise from pre-existing chloroplasts within a cell. The origin of the chloroplast is ultimately traced back to free-living bacteria that are the ancestors of modern cyanobacteria, a group of bacteria that perform oxygenic photosynthesis. Chloroplast evolution started when an ancestral cyanobacterium was engulfed by a cell containing the nucleus and mitochondria, and became an endosymbiont, an organism living within a cell of another organism. The successful conversion to the chloroplast required the endosymbiont to transfer most of its genes to the nucleus of the host cell. This gene transfer depended on the establishment of protein import machinery that allowed uptake of the nuclear-encoded proteins at the outer and inner envelope membranes of the endosymbiont. Although the concept of this evolutionary process has been widely recognized, its underlying mechanisms remain largely unknown. The project aims to address this problem by defining the function of a chloroplast protein called OEP80. OEP80 is evolutionarily related to the protein import channel Toc75. Both OEP80 and Toc75 are present in the chloroplast outer envelope membrane and are essential for the viability of plants at the embryonic stage. The channels are believed to have been derived from a protein in the endosymbiont and to have diverged early in the evolution of chloroplasts. Hence, the gene duplication that gave rise to Toc75 and OEP80 must have been a critical step in the evolution of chloroplasts. In contrast to Toc75, however, the exact role of OEP80 remains elusive. To define the function of OEP80, this project will utilize genetic engineering to generate various mutated plants that lack this protein at certain developmental stages or accumulate modified forms of it. The project will also define the molecular characteristics of OEP80 in the chloroplast outer envelope membrane. Outcomes of these experiments will help develop a focused hypothesis regarding the molecular bases of the evolution of the organelle protein import machinery. Moreover, this project will reveal novel insights into the function of membrane proteins and the role of chloroplasts in plant development.
This project will involve graduate students, a postdoctoral scholar, and undergraduate students from UC Davis and a local postsecondary minority institution. Students will be provided with excellent opportunities to work together and learn various genetic and biochemical techniques as well as critical thinking in biology. The research findings will be distributed to scientific groups via presentations at national meetings and publications in peer-reviewed journals, and also to non-scientific groups at a non-science major undergraduate general education class in UC Davis. The postdoctoral scholar will be trained in communication and presentations at those occasions.
