Date of Award
Doctor of Philosophy
Genetics, Development and Cell Biology
Steven R. Rodermel
The immutans variegation mutant of Arabidopsis has green and white sectored leaves due to lack of IMMUTANS (IM), a plastid membrane terminal oxidase that transfers electrons from plastoquinone to molecular oxygen. IM bears similarity to alternative oxidase (AOX) of mitochondrial inner membranes. IM functions in a number of redox pathways, including carotenoid biosynthesis and chlororespiration, and its activity is especially important early in chloroplast biogenesis when the photosynthetic electron transport chain is not yet fully functional. To gain insight into factors that are able to compensate for a lack of IM in the green sectors of immutans, we initiated a second site suppressor screen to identify mutants of im that have a non-variegated, all-green phenotype. We report that suppression of variegation in ATG791, an activation-tagged im line, is due to over-expression of the gene for mitochondrial AOX2. AOX2 is present and functional in chloroplast thylakoids of this line, and its presence there does not perturb steady state photosynthesis, at least under standard lab conditions. The finding that AOX2 is able to substitute for IM is surprising given that the genes for these two proteins diverged prior to the endosymbiotic events that gave rise to the eukaryotic plant cell, and they have very different substrate-specificities, functional domains, and modes of regulation, presumably optimized for function in different membrane milieu in different cellular compartments. Our results raise the intriguing possibility that AOX2 is normally dual-targeted to mitochondria and chloroplasts.
Liu, Huiying, "The study of the mechanism of Arabidopsis immutans variegation" (2009). Graduate Theses and Dissertations. 11239.