PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Global regulation of photosynthesis genes in response to oxidative stress in the cyanobacterium Synehchocystis sp. PCC 6803. Abhay Singh¹, Hong Li¹, Louis Sherman^*,1, ¹ Purdue University, West Lafayette, IN, USA

ABSTRACT- All organisms have developed specific defenses and global responses that enable them to survive oxidative stress. We are interested in the regulatory mechanisms used by cyanobacteria to protect the photosynthetic apparatus against oxidative damage, specifically by peroxides. We have utilized a full genome microarray for the unicellular, transformable cyanobacterium Synechocystis sp PCC 6803 to study differential gene expression induced by peroxide (1,2). We have also developed procedures that have enabled us to identify differential gene expression with a high level of precision and with the ability to analyze expression changes greater than ±25%. We will concentrate on two themes from this work-- the expression of specific genes such as isiA and regulatory networks that affect the photosynthetic apparatus. The isiA gene, encoding the novel Chl-binding protein CP43', was induced over 20-fold under both low iron and short-term peroxide stress conditions. In addition, isiA transcription is highly sensitive to many other changes in conditions, and we must now relate this molecular regulation to the possible functions of isiA. The transcription of the main structural genes of the photosynthetic apparatus was not substantially altered by short-term peroxide stress, but transcription of the genes involved in chlorophyll and phycobilisome biosynthesis decreased. We have also determined that there is a peroxide regulon that is controlled by a PerR gene (slr1738) that is related to a similar gene in Bacillus subtilis. Genes in this regulon encode for proteins involved in the assembly of FeS proteins and those thought to have a protective function for PSII. Interestingly, isiA is more resistant to peroxide under all conditions studied (±Fe; exponential vs. stationary growth). We have identified other genes involved in the assembly or protection of photosynthetic complexes. We will develop a working model for the cellular response to oxidative stress and the adequate functioning of the photosynthetic apparatus. 1. Postier, B., H Wang, AK Singh, 7 others, LA Sherman, RL Burnap.2003. BMC Genomics 4:23-33. 2. Hong Li, AK Singh, LM McIntyre and LA Sherman. 2004.Differential gene expression in response to hydrogen peroxide and the putative PerR regulon of Synechocystis sp. PCC 6803.J. Bacteriol. June 2004.

KEY WORDS: regulation, photosynthesis, oxidative stress, microarray