PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Both CP43' and Flavodoxin play a role in protection from heat and oxidative stresses. Kouji Kojima^*,1, Hitoshi Nakamoto¹, ¹ Saitama university, Saitama, Japan

ABSTRACT- The isiA and isiB genes in Synechocystis sp. PCC 6803 form a dicistronic operon and their expression is tightly regulated by iron availability. CP43', a chlorophyll a binding protein, forms antenna complex surrounding the photosystem I. Flavodoxin is an alternative protein of ferredoxin to act as an electron acceptor from the photosystem I complex. Recently, it was reported that this operon is induced under oxidative or heat stress conditions as well as iron deficiency. The aim of this study is to evaluate their physiological roles for acquisition of oxidative and heat-stress tolerances by the use of the isiAB and isiB disruptants of Synechocystis sp. PCC 6803. In the isiAB mutant, the isiB gene was transcriptionally inactivated by the insertion of an antibiotic resistant gene into the isiA gene. We analyzed phenotypes of cells grown in the presence of 5 M methylviologen under the light intensity of 20 E/m²/s. Both mutants were more sensitive to this stress than the wild type, suggesting that the isiAB operon plays a role in the protection from oxidative stress. Next, we analyzed growth at 42^oC, a moderately high temperature. The isiAB mutant stopped growing after the temperature shift-up and could not survive, while the wild type could grow. The isiB mutant continued growth at a slower rate than the wild type. Under lethal high-temperature conditions at 48^oC for 15 min, the survival rate of the isiAB mutant was 0.0098%, while those of the wild type and the isiB mutant were 3.7% and 0.75%, respectively. These results indicate the importance of the isiAB operon in the thermal stress management. We suggest that CP43' and flavodoxin play an important role in regulating the supply and the usage of light energy to suppress the generation of active oxygen species through the operation of the photosynthetic electron transport system.

KEY WORDS: flavodoxin, CP43', photosystem, cyanobacterium