Oxidation of P700 in Photosystem I Is Essential for the Growth of Cyanobacteria

Abstract

The photoinhibition of photosystem I (PSI) is lethal to oxygenic phototrophs. Nevertheless, it is unclear how photodamage occurs or how oxygenic phototrophs prevent it. Here, we provide evidence that keeping P700 (the reaction center chlorophyll in PSI) oxidized protects PSI. Previous studies have suggested that PSI photoinhibition does not occur in the two model cyanobacteria, Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942, when photosynthetic CO 2 fixation was suppressed under low CO 2 partial pressure even in mutants deficient in flavodiiron protein (FLV), which mediates alternative electron flow. The lack of FLV in Synechococcus sp. PCC 7002 (S. 7002), however, is linked directly to reduced growth and PSI photodamage under CO 2 -limiting conditions. Unlike Synechocystis sp. PCC 6803 and S. elongatus PCC 7942, S. 7002 reduced P700 during CO 2 -limited illumination in the absence of FLV, resulting in decreases in both PSI and photosynthetic activities. Even at normal air CO 2 concentration, the growth of S. 7002 mutant was retarded relative to that of the wild type. Therefore, P700 oxidation is essential for protecting PSI against photoinhibition. Here, we present various strategies to alleviate PSI photoinhibition in cyanobacteria.Low CO 2 fixation efficiency in the Calvin-Benson cycle prevents the utilization of NADPH and ATP in photosynthesis and causes these molecules to accumulate, resulting in oxidative photosynthetic cell damage. High light, low temperature, and CO 2 limitation increase NADPH and ATP levels beyond the Calvin-Benson cycle requirements. Electrons and H +

The Liverwort, Marchantia, Drives Alternative Electron Flow Using a Flavodiiron Protein to Protect PSI

“…5F). These data suggest that FLV-mediated AEF is required to maintain P700 in an oxidized state under fluctuating light in M. polymorpha, which is similar to observations of the cyanobacterium S. 6803 (Allahverdiyeva et al, 2013;Shimakawa et al, 2016b). ) was turned on at the zero time point.…”

“…1A). In plant leaves and cyanobacterial cells, photoinhibition of PSI is alleviated by the oxidation of P700, owing to a decrease in the amount of photooxidizable P700 (Sejima et al, 2014;Shimakawa et al, 2016b). These data indicate that FLVmediated AEF contributes to the oxidation of P700 in M. polymorpha.…”

“…In fact, in some species of cyanobacteria (S. 6803, Synechococcus elongatus PCC 7942, and Synechococcus sp. PCC 7002), under suppressed photosynthesis conditions equilibrated with air, AEF is driven by FLVs, not by photorespiration (Hayashi et al, 2014;Shimakawa et al, 2015Shimakawa et al, , 2016bShaku et al, 2016). Furthermore, some eukaryotic algae, including the green alga Chlamydomonas reinhardtii and the diatom Phaeodactylum tricornutum, do not utilize photorespiration as the main alternative electron sink under suppressed photosynthesis conditions (Shimakawa et al, 2016a(Shimakawa et al, , 2017.…”

Diverse strategies of O2 usage for preventing photo-oxidative damage under CO2 limitation during algal photosynthesis

“…Also, photorespiration can be explained as an O 2 -dependent AEF in the broad sense171819. A large O 2 -dependent AEF that replaces photosynthesis can alleviate photoinhibition by dissipating excess energy to O 2 111213171819202122. Recently, we showed that an O 2 -dependent AEF is essential for the oxidation of P700 under CO 2 limitation to protect PSI against photo-oxidative damage in the cyanobacterium Synechococcus sp.…”

“…Recently, we showed that an O 2 -dependent AEF is essential for the oxidation of P700 under CO 2 limitation to protect PSI against photo-oxidative damage in the cyanobacterium Synechococcus sp. PCC 7002 (S. 7002)2223. That is, oxygenic phototrophs accessed O 2 to prevent photo-oxidative damage derived from O 2 .…”