Abstract
A limitation in carbon dioxide (CO&sub2;), which occurs as a result of natural environmental variation, suppresses photosynthesis and has the potential to cause photo-oxidative damage to photosynthetic cells. Oxygenic phototrophs have strategies to alleviate photo-oxidative damage to allow life in present atmospheric CO&sub2; conditions. However, the mechanisms for CO&sub2; limitation acclimation are diverse among the various oxygenic phototrophs, and many mechanisms remain to be discovered. In this study, we found that the gene encoding a CO&sub2; limitation-inducible protein, ColA, is required for the cyanobacterium Synechococcus sp. PCC 7002 (S. 7002) to acclimate to limited CO&sub2; conditions. An S. 7002 mutant deficient in ColA (ΔcolA) showed lower chlorophyll content, based on the amount of nitrogen, than that in S. 7002 wild-type (WT) under ambient air but not high CO&sub2; conditions. Both thermoluminescence and protein carbonylation detected in the ambient air grown cells indicated that the lack of ColA promotes oxidative stress in S. 7002. Alterations in the photosynthetic O&sub2; evolution rate and relative electron transport rate in the short-term response, within an hour, to CO&sub2; limitation were the same between the WT and ΔcolA. Conversely, these photosynthetic parameters were mostly lower in the long-term response of a few days in ΔcolA than in the WT. These data suggest that ColA is required to sustain photosynthetic activity for living under ambient air in S. 7002. The unique phylogeny of ColA revealed diverse strategies to acclimate to CO&sub2; limitation among cyanobacteria.