Date of Award
Doctor of Philosophy
Genetics, Development and Cell Biology
Steven R. Rodermel
The Arabidopsis variegation2 (var2) mutant, displaying a conspicuous green and white sectoring phenotype, is one of the most well-characterized variegation mutants and is the caused by mutations in VAR2, which encodes a subunit of the FtsH metalloprotease complex situated in the chloroplast thylakoid membranes. FtsH proteins mediate a myriad of processes in plants, the most prominent one being the turnover of photosystem II reaction center D1 protein.
The Rodermel lab is interested in using the unique variegation phenotype of var2 mutant as a tool to study the mechanism of variegation and the regulation of chloroplast biogenesis. To this end, our lab has carried out second-site var2 genetic suppressor screens to obtain mutants with non-variegation phenotype despite the var2 mutant background.
Previous work with several var2 suppressors carried out in our lab and others' has uncovered an unexpected link between var2 variegation and chloroplast translation. A number of suppressor lines have defects in chloroplast rRNA processing and/or chloroplast translation.
My research has been primarily focused on two var2 suppressor lines, 004-003 (var2-5 svr7-1) and TAG-11 (var2-5 svr3-1). The molecular cloning of the two suppressor genes revealed that SVR7 is a chloroplast PPR (Pentatricopeptide Repeat) protein that might function in nucleic acids binding whereas SVR3 is a chloroplast homolog of the prokaryotic TypA translation elongation factor. Consistent with the link between var2 and chloroplast translation, both mutant lines have distinct chloroplast rRNA processing defects. Interestingly, I also found that var2 and svr3 single mutants are both chilling sensitive and that they display a pronounced chlorosis phenotype at low temperatures. These findings reinforced the known relationship between chloroplast translation and chilling stress and also the connection between VAR2 function and chloroplast translation.
Extending from the var2 suppressor work , I also carried out research that led to the identification of a putative chloroplast protease, VirX, and the generation a var2-4 near isogenic line in the Landsberg erecta ecotype background.
Liu, Xiayan, "var2 genetic suppressors" (2010). Graduate Theses and Dissertations. 11956.