Minisymposium 4: Oxidative stress

Abs # 14003: Comparative proteomics of the light stress response of the thylakoid membrane in chloroplasts of wild-type and the ascorbate-deficient vtc2 mutant in Arabidopsis thaliana

Presenter:	Giacomelli, Lisa , lg76@cornell.edu
Authors	Giacomelli, Lisa  (A)   van Wijk, Klaas J. (A)
Affiliations:	(A): Department of Plant Biology, Cornell University

An extensive characterization of the thylakoid proteome of Arabidopsis thaliana (Friso et al. (2004) Plant Cell 16(2): 478-99; Peltier et al. (2002) Plant Cell 14(1): 211-36) visualized the expression of a number of proteins, such as isomerases, chaperones, fibrillins, peroxiredoxins, m-type thioredoxins and ascorbate peroxidases. Together they form a complex network of activities in terms of stress defense, protein (un)folding, and repair in and around the thylakoid membrane. However, it is unclear to what extent their expression levels and activities are coordinated. These proteins were identified through a combination of different protein separation techniques, mass spectrometry and bioinformatics. A genome-wide screening using subcellular predictors identified additional proteins of this network. A public database with the identified thylakoid proteome is now available (http://cbsusrv01.tc.cornell.edu/users/ppdb/). The aim of this project is to understand how these identified proteins –and possibly additional proteins- are co-regulated in response to light stress. Combining comparative proteomics and A. thaliana mutants partially impaired in the oxidative stress defense system, we aim to follow the differential expression of these proteins. This will provide insights in the contribution of the different thylakoid proteins during stress response, as well as the consequences for the photosynthetic apparatus. Ascorbate (Vitamin C) is a water soluble antioxidant, which helps detoxification of reactive oxygen species produced in the chloroplast under stress conditions, such as excess of light. The A. thaliana vtc2 mutant has reduced accumulation of ascorbate, and shows reduced non photochemical quenching under high light (Muller-Moule, et al. (2002) Plant Physiol 128(3): 970-7). The mutant has been subjected to light stress treatments, and chloroplasts sub-proteomes analyzed by different techniques. Here we present the response of the soluble and peripherally attached thylakoid proteomes of wild-type and vtc2 mutant to the transition from low to high light. Differential protein expression is determined by 2-dimensional gels and image analysis. The affected proteins are identified by mass spectrometry and bioinformatics.