Poster: Redox regulation

Abs # 237: The mechanism of variegation in the immutans mutant of Arabidopsis thaliana

Presenter:	Liu, Huiying , hyliu@iastate.edu
Authors	Liu, Huiying  (A)   Barr, Jason  (A)   Rodermel, Steven  (A)
Affiliations:	(A): Department of Genetics, Developmental and Cellular Biology, Iowa State University, Ames, Iowa 50011, USA

Variegation mutants provide an ideal system to dissect communication between the nucleus-cytoplasm, the chloroplast, and the mitochondrion. The immutans (im) mutant of Arabidopsis is a nuclear gene-induced variegation mutant that contains green and white sectors. The green ones contain cells with morphologically normal chloroplasts; whereas the white ones contain abnormal, pigment-deficient plastids. Early studies showed that the white im sectors accumulate the carotenoid precursor phytoene. Cloning of the IMMUTANS (IM) gene revealed that it is a plastid homolog of the mitochondrial alternative oxidase (AOX). Early hypotheses have been confirmed that IM is a quinol oxidase (like AOX), and that it functions early in the biogenesis of chloroplasts as a component of a redox chain in carotenoid biosynthesis. In this chain, electrons are transferred from phytoene via phytoene desaturase to the plastoquinone pool, and from plastoquinol (via IM) to oxygen. Recent studies have revealed that IM plays a large role in plastid metabolism: it functions as the terminal oxidase of chlororespiration, as well as a light-stress protein. Although many studies have examined IM function at a biochemical level, the mechanism of im variegation has not been explored. Suppressor analyses should supply useful clues about this mechanism. In these analyses, the goal is to isolate genes for proteins that, when mutated, reverse the variegation phenotype of immutans. We have used two procedures to isolate second site suppressors: ems mutagenesis and activation-tagging. The rationale behind the latter is that overexpression of a gene for an “IM compensating activity” might suppress the im variegation phenotype. In this poster we will outline our progress in isolating and cloning immutans suppressors.