Sub‐cellular location of FtsH proteases in the cyanobacterium Synechocystis sp. PCC 6803 suggests localised PSII repair zones in the thylakoid membranes

Abstract

SummaryIn cyanobacteria and chloroplasts, exposure to HL damages the photosynthetic apparatus, especially the D1 subunit of Photosystem II. To avoid chronic photoinhibition, a PSII repair cycle operates to replace damaged PSII subunits with newly synthesised versions. To determine the sub‐cellular location of this process, we examined the localisation of FtsH metalloproteases, some of which are directly involved in degrading damaged D1. We generated transformants of the cyanobacterium S ynechocystis sp. PCC6803 expressing GFP‐tagged versions of its four FtsH proteases. The ftsH2–gfp strain was functional for PSII repair under our conditions. Confocal microscopy shows that FtsH1 is mainly in the cytoplasmic membrane, while the remaining FtsH proteins are in patches either in the thylakoid or at the interface between the thylakoid and cytoplasmic membranes. HL exposure which increases the activity of the Photosystem II repair cycle led to no detectable changes in FtsH distribution, with the FtsH2 protease involved in D1 degradation retaining its patchy distribution in the thylakoid membrane. We discuss the possibility that the FtsH2–GFP patches represent Photosystem II ‘repair zones’ within the thylakoid membranes, and the possible advantages of such functionally specialised membrane zones. Anti‐GFP affinity pull‐downs provide the first indication of the composition of the putative repair zones.

Early emergence of the FtsH proteases involved in photosystem II repair

“…However, the FtsH2/3 complex is not restricted to PSII repair and participates in the removal of unassembled membrane proteins (Komenda et al 2006) as well as soluble proteins (Stirnberg et al 2007). Also present in Synechocystis 6803 are FtsH1/FtsH3 heterocomplexes located in the cytoplasmic membrane (Krynická et al 2014) and FtsH4 homo-complexes in the thylakoid and possibly cytoplasmic membrane (Boehm et al 2012, Sacharz et al 2015. Both FtsH1 and FtsH3 are crucial for cell viability whereas FtsH2 and FtsH4 are dispensable (Mann et al 2000), although growth of mutants lacking FtsH2 is extremely light-sensitive (Silva et al 2003).…”

Transcriptional response of Prochlorococcus to co-culture with a marine Alteromonas: differences between strains and the involvement of putative infochemicals

“…In 9313 + diluted 1A3, six genes involved in the repair of DNA mismatch or single-strand breaks were more abundantly expressed, suggesting potentially a higher level of cellular stress. In 9313+1A3, a clearer signal of cellular stress was observed: in addition to three genes involved in DNA repair, the stress-related protein chaperones Hsp90 and Hsp100 (ClpB) were more abundantly expressed, as were two proteases including one (FtsH3) predicted to be involved in repair of photosystem 1 proteins (Sacharz et al, 2015). Notably, many of the genes involved in DNA damage repair were actually less abundantly expressed in MED4+1A3 (for example, recR, recO and recC), as was ftsH4 (an ortholog of ftsH3 mentioned above), lending further supports the hypothesis that MED4 is sensing significantly lower cell stress compared with MIT9313, when growing with the same density of heterotrophs.…”

Thylakoid Membrane Architecture in Synechocystis Depends on CurT, a Homolog of the Granal CURVATURE THYLAKOID1 Proteins

“…When chlorophyll autofluorescence indicative of thylakoid membranes was visualized in the same cell, only a partial overlap with the CurT-CFP signal was observed ( Figure 8; Supplemental Movies 1 to 3). Strikingly, the peripheral CurT-CFP signals frequently reached their maximal intensity in those areas where chlorophyll fluorescence was low, i.e., where thylakoid convergence zones are expected to form (Sacharz et al, 2015). This becomes even clearer when the intensity of a circumferential profile that follows the thylakoid's fluorescence signal is quantified separately for each of the two fluorescent channels ( Figure 8C).…”

“…Subsequently, precomplexes migrate laterally into thylakoid lamellae, where their assembly is completed (Nickelsen and Rengstl, 2013). Recently, evidence based on the subcellular distribution of the D1 degradationrelated FtsH protease and the PSII repair factor Slr0151 (Yang et al, 2014;Sacharz et al, 2015;Rast et al, 2016), has been obtained that maintenance, i.e., the repair, of PSII is also localized at or near these areas. However, whether or not plasma and thylakoid membranes fuse at these sites has not yet been resolved (Liberton et al, 2006;van de Meene et al, 2006;van de Meene et al, 2012).…”