In the aquatic environment of cyanobacteria, the CO2 concentration often is limiting for photosynthesis, and when combined with high light, this leads to the formation of excess reactive oxygen species (ROS). ROS cause damage to most cellular constituents (membranes, DNA, and proteins), and photosystem II (PSII) is especially vulnerable as it is a primary site of ROS formation that occurs in the chloroplast under high light and low CO2 (reviewed in Bailey and Grossman, 2008; Tikkanen et al., 2011). Zhang et al. (1952?971) report on a novel type of photoprotection mechanism in cyanobacteria encoded by the flv4-flv2 operon. This operon is present in a number of cyanobacteria and is strongly induced upon low Ci and high light conditions in Synechocystis (Zhang et al., 2009). Three genes found in the operon are arranged in tandem orientation in the same direction of transcription (flv4, Sll0218, and flv2), suggesting an interaction of these proteins. Flv4 and Flv2 encode flavodiiron proteins (FDPs), whereas Sll0218 encodes a hypothetical protein of unknown function. In many strict and facultative anaerobic microorganisms, FDPs are known to function in detoxification of O2 and/or NO (Vicente et al., 2008). Through investigation of the localization of these three proteins in Synechocystis and evaluation of mutant strains, Zhang et al. provide insight into their function in photoprotection of PSII.
展开▼
