The Stromal Chloroplast Deg7 Protease Participates in the Repair of Photosystem II after Photoinhibition in Arabidopsis    

Abstract

Light is the ultimate source of energy for photosynthesis; however, excessive light leads to photooxidative damage and hence reduced photosynthetic efficiency, especially when combined with other abiotic stresses. Although the photosystem II (PSII) reaction center D1 protein is the primary target of photooxidative damage, other PSII core proteins are also damaged and degraded. However, it is still largely unknown whether degradation of D1 and other PSII proteins involves previously uncharacterized proteases. Here, we show that Deg7 is peripherally associated with the stromal side of the thylakoid membranes and that Deg7 interacts directly with PSII. Our results show that Deg7 is involved in the primary cleavage of photodamaged D1, D2, CP47, and CP43 and that this activity is essential for its function in PSII repair. The double mutants deg5 deg7 and deg8 deg7 showed no obvious phenotypic differences under normal growth conditions, but additive effects were observed under high light. These results suggest that Deg proteases on both the stromal and luminal sides of the thylakoid membranes are important for the efficient PSII repair in Arabidopsis (Arabidopsis thaliana).

Downregulation of chloroplast protease AtDeg5 leads to changes in chronological progression of ontogenetic stages, leaf morphology and chloroplast ultrastructure in Arabidopsis

“…Specifically, it was demonstrated for AtDeg1, 7 and 8 that recombinant versions of these enzymes catalyze in vitro degradation of photodamaged PSII reaction center protein PsbA (D1) which in vivo is inherent to PSII repair cycle. The results have suggested that the photodamaged PsbA protein is cleaved in vivo by introduction of multiple cuts by cooperating AtDegs 1, 5/8, 7 and probably AtDeg2 as well [12,[14][15][16][17]. Similarly, recombinant version of AtDeg1 and AtDeg7 has been demonstrated to be responsible for in vitro degradation of PsbD, PsbS, Lhcb4 and cytb6 as well as PsbB-D, respectively under photoinhibitory conditions [12,18].…”

“…The results have suggested that the photodamaged PsbA protein is cleaved in vivo by introduction of multiple cuts by cooperating AtDegs 1, 5/8, 7 and probably AtDeg2 as well [12,[14][15][16][17]. Similarly, recombinant version of AtDeg1 and AtDeg7 has been demonstrated to be responsible for in vitro degradation of PsbD, PsbS, Lhcb4 and cytb6 as well as PsbB-D, respectively under photoinhibitory conditions [12,18]. Later it was demonstrated in a more direct way that Lhcb6 and PsbF apoproteins are degraded in a stress-related manner by AtDeg2 and AtDeg5, respectively [16,19].…”

“…It was demonstrated that a linear structure of chloroplasttargeted AtDeg proteases involves one or two protease domains (if the second protease domain is present -it is a catalytically inactive version [10]) and 0 to 4 of PDZ domains which are thought to mediate formation of proteolytically active oligomeric forms [11] and select proper substrates [12]. In fact, several lines of evidence show that chloroplasttargeted AtDeg proteases exist as both homo-and heterooligomeric assemblies with trimer as a basic structural unit.…”

MET1 Is a Thylakoid-Associated TPR Protein Involved in Photosystem II Supercomplex Formation and Repair in Arabidopsis

“…Additionally, the lumenal peptidase CtpA is specifically required for C-terminal processing of the D1 protein (Anbudurai et al, 1994;Oelmüller et al, 1996;Yamamoto et al, 2001); in the absence of this C-terminal processing, no active PSII complex can be formed (Che et al, 2013). Thylakoid bound FtsH and Deg proteases play an important role in degrading damaged D1 (Kapri-Pardes et al, 2007;Sun et al, 2010aSun et al, , 2010bChi et al, 2012b;Kato et al, 2012), even if these proteases are not specific to PSII. Thylakoid protein translocons SecY/E and ALBINO3 (ALB3) have been shown to interact with each other (Klostermann et al, 2002) and are required for co-and posttranslational insertion of plastid-and nuclear-encoded proteins, including components of the PSII reaction center/core complex (Moore et al, 2000;Zhang et al, 2001;Peng et al, 2006;Ma et al, 2007;Cai et al, 2010;Schneider et al, 2014) (reviewed in Richter et al, 2010;Celedon and Cline, 2013).…”

Quality control of Photosystem II: The molecular basis for the action of FtsH protease and the dynamics of the thylakoid membranes

“…This explains the mechanism of the donor-side photoinhibition of PSII. More recently, it was also suggested that lipid peroxidation induced by strong illumination accelerates the damage Historically, the Deg protease was first proposed as a protease candidate [31,37,38,47], but there has been controversy over the exact roles of Deg and FtsH in the proteolytic process of the photodamaged D1 protein [32,[48][49][50]. The discussion on this issue is ongoing with newly obtained data.…”