PARENT SESSION

Symposium S7D Chloroplast factories and transformation
Thursday September 2nd, 2004 2:40 PM-4:40 PM Room 510A
Chair: Dick Sayre
Co-Chair: Pal Maliga

Variegation mutants and the regulation of photosynthetic processes. Steven Rodermel^*,1, ¹ Iowa State University, Ames, IA, USA

ABSTRACT- Variegation mutants of Arabidopsis are attractive models for studying nuclear-organelle interactions and for identifying components that are required for photosynthesis. The leaves of these mutants contain green and white sectors. Whereas cells in the white sectors contain non-functional plastids that lack pigments and lamellar structures, the green sectors contain morphologically-normal chloroplasts. We have focused on two variegations (immutans and var2) that are due to mutations in nuclear genes. These mutants have a uniform genetic constitution, but intriguingly, the mutant phenotype is expressed only in the white sectors. Map-based cloning has revealed that IMMUTANS codes for a chloroplast homolog of the mitochondrial alternative oxidase (AOX). AOX is an alternate terminal oxidase to the cytochrome c oxidase in the respiratory pathway of plants. Evidence indicates that IM functions as a quinol oxidase in plastid membranes and that it plays a role in carotenoid biosynthesis. IM might also serve as general electron sink and mediate plant responses to oxidative stress. Map-based cloning has revealed that VAR2 is a homolog of bacterial FtsH, a zinc metalloprotease that functions in protein quality control and in the folding of membrane proteins. VAR2 appears to be involved in the modeling of thylakoid membranes during chloroplast development. var2 and immutans are both null alleles, suggesting that the green sectors in both mutants arise from compensatory mechanisms. Suppressor analyses have given insight into these mechanisms; results of these analyses will be discussed.

KEY WORDS: IMMUTANS, Variegation, VAR2, FtsH