Electron transport regulates exchange of two forms of photosystem II D1 protein in the cyanobacterium Synechococcus.

Abstract

Synechococcus sp. PCC 7942 modulates photosynthetic function by transiently replacing the constitutive D1 photosystem II protein, D1:1, with an alternate form, D1:2, to help counteract photoinhibition under excess light. We show that a temperature drop from 37 to 25 degrees C also drives D1:1/D1:2 exchange under constant, moderate light. Chilling or light‐induced D1 exchange results from rapid loss of psbAI message coding for D1:1 and accumulation of psbAII and psbAIII messages coding for D1:2. During chilling, a large pool of a novel form, D1:2*, transiently accumulates, distinguishable from normal D1 by an increase in apparent molecular mass. D1:2* is not phosphorylated and is probably a functionally inactive, incompletely processed precursor. After acclimation to 25 degrees C, D1:2* disappears and D1:1 again predominates, although substantial D1:2 remains. Partial inhibition of electron transport under constant, moderate light also triggers the D1 exchange process. These treatments all increase excitation pressure on photosystem II relative to electron transport. Therefore, information from photosynthetic electron transport regulates D1 exchange without any requirement for a change in light intensity or quality, possibly via a redox sensing mechanism proximal to photosystem II.

Induction of the heat shock protein ClpB affects cold acclimation in the cyanobacterium Synechococcus sp. strain PCC 7942

“…The extent of this drop in photosynthetic electron transport is consistent with that previously observed in wild-type Synechococcus spp. acclimated to 25°C (2). In contrast, the ⌬clpB strain continued to lose activity after the initial drop, with only 25% activity remaining after 8 h at 25°C.…”

“…Cell cultures were grown in BG-11 inorganic medium (30) buffered with 10 mM 3-(N-morpholino) propanosulfonic acid (pH 7.5) and bubbled with 5% CO 2 in air (1 ml s Ϫ1 ) at 37 or 25°C with continuous, even illumination of 50 mol of photons m Ϫ2 s Ϫ1 (2). Batch cultures were inoculated from liquid precultures to a concentration of 0.5 g of chlorophyll (Chl) ml Ϫ1 .…”

“…Chl a fluorescence parameters and oxygen evolution were measured simultaneously at 37 and 25°C with a pulse amplitude modulated fluorometer (Walz, Effeltrich, Germany) and a Clark-type oxygen electrode (Hansatech, King's Lynn, United Kingdom), respectively, as previously described in detail (2,4). The degree of inhibition of photosystem II and photosynthetic electron transport was monitored by determining the parameters of maximal photochemical efficiency (F V /F M ) and oxygen evolution (mol of O 2 mg of Chl Ϫ1 h Ϫ1 ), respectively.…”

A Redox-Responsive Regulator of Photosynthesis Gene Expression in the Cyanobacterium Synechocystis sp. Strain PCC 6803

“…strain PCC 7942, there are two forms of D1 protein, D1:1 and D1:2. It has been demonstrated that PSII reaction centers containing D1:2 have a higher intrinsic resistance to photoinhibition and are more photochemically efficient than PSII centers with D1:1 (9,12,13,30). In Synechocystis sp.…”

Chloroplast redox signals: how photosynthesis controls its own genes

“…However, redox regulation of cyanobacterial gene expression is not restricted to the PQ pool alone. Additional redox signals come from PSII excitation pressure and the thiol state of the cell [51,52]. Furthermore, as well as the reaction-centre genes, several other genes are also regulated by signals from electron transport, generated either photosynthetically or from glucose metabolism.…”