Identification of a cyanobacterial CRR6 protein, Slr1097, required for efficient assembly of NDH‐1 complexes in Synechocystis sp. PCC 6803

Abstract

These authors contributed equally to this work. SUMMARYDespite significant progress in clarifying the subunit compositions and functions of the multiple NADPH dehydrogenase (NDH-1) complexes in cyanobacteria, the subunit maturation and assembly of their NDH-1 complexes are poorly understood. By transformation of wild-type cells with a transposon-tagged library, we isolated three mutants of Synechocystis sp. PCC 6803 defective in NDH-1-mediated cyclic electron transfer and unable to grow under high light conditions. All the mutants were tagged in the same slr1097 gene, encoding an unknown protein that shares significant homology with the Arabidopsis protein chlororespiratory reduction 6 (CRR6). The slr1097 product was localized in the cytoplasm and was required for efficient assembly of NDH-1 complexes. Analysis of the interaction of Slr1097 with 18 subunits of NDH-1 complexes using a yeast two-hybrid system indicated a strong interaction with NdhI but not with other Ndh subunits. Absence of Slr1097 resulted in a significant decrease of NdhI in the cytoplasm, but not of other Ndh subunits including NdhH, NdhK and NdhM; the decrease was more evident in the cytoplasm than in the thylakoid membranes. In the Δslr1097 mutant, NdhH, NdhI, NdhK and NdhM were hardly detectable in the NDH-1M complex, whereas almost half the wild-type levels of these subunits were present in NDH-1L complex; similar results were observed in the NdhI-less mutant. These results suggest that Slr1097 is involved in the maturation of NdhI, and that assembly of the NDH-1M complex is strongly dependent on this factor. Maturation of NdhI appears not to be crucial to assembly of the NDH-1L complex.

Subunit Q Is Required to Stabilize the Large Complex of NADPH Dehydrogenase in Synechocystis sp. Strain PCC 6803

“…This approach has been extensively used to monitor NDH-CET activity in cyanobacteria Deng et al, 2003;Ma and Mi, 2005;Battchikova et al, 2011a;Dai et al, 2013;Zhang et al, 2014;Zhao et al, 2014) and higher plants (Burrows et al, 1998;Shikanai et al, 1998;Hashimoto et al, 2003;Wang et al, 2006;Peng et al, 2009Peng et al, , 2011bPeng et al, , 2012Sirpiö et al, 2009;Yamamoto et al, 2011;Armbruster et al, 2013). As shown in Figure 1B, the NDH-CET activity in both mutants was lower than that in the wild type as judged by the height and relative rate of postillumination increase in Chl fluorescence.…”

“…The NDH-CET has a protective role against high light stress in cyanobacteria (Battchikova et al, 2011a;Dai et al, 2013;Zhang et al, 2014;Zhao et al, 2014) and higher plants (Endo et al, 1999). Under high light conditions, therefore, the growth of NDH-CET-defective mutants is markedly retarded compared with the wild type, despite similar growth under moderate light irradiation.…”

“…The NDH-CET plays an important role in coping with various environmental stresses, regardless of its elusive mechanism. For example, this function can greatly alleviate high light-sensitive growth phenotypes (Endo et al, 1999;Battchikova et al, 2011a;Dai et al, 2013;Zhang et al, 2014;Zhao et al, 2014). Therefore, high light strategy can help in identifying the proteins essential to NDH-CET.…”

O2-dependent large electron flow functioned as an electron sink, replacing the steady-state electron flux in photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803, but not in the cyanobacterium Synechococcus sp. PCC 7942

“…In fact, a mutant of S. 6803 deficient in the CRR6, an assembly factor of NDH, is impaired with suppressed photosynthesis under high light conditions. 17) Recently, photorespiration was proposed to function in S. 6803, which has a carbon recovery pathway different from that of higher plants. [18][19][20] In S. 6803 mutants deficient in photorespiratory enzymes, photosynthesis and cell growth are suppressed.…”

“…13,14) In the fourth part, a cyclic electron flow (CEF) around PSI functions as AEF in cyanobacteria. 17) CEF is catalyzed by NADH dehydrogenase (NDH), which contributes to the cellular CO 2 concentration. CEF stimulates photosynthesis, which contributes to the protection of PSII from photoinhibition.…”