The Thylakoid Lumen Protease Deg1 Is Involved in the Repair of Photosystem II from Photoinhibition in Arabidopsis

Abstract

Deg1 is a Ser protease peripherally attached to the lumenal side of the thylakoid membrane. Its physiological function is unknown, but its localization makes it a suitable candidate for participation in photoinhibition repair by degradation of the photosystem II reaction center protein D1. We transformed Arabidopsis thaliana with an RNA interference construct and obtained plants with reduced levels of Deg1. These plants were smaller than wild-type plants, flowered earlier, were more sensitive to photoinhibition, and accumulated more of the D1 protein, probably in an inactive form. Two C-terminal degradation products of the D1 protein, of 16 and 5.2 kD, accumulated at lower levels compared with the wild type. Moreover, addition of recombinant Deg1 to inside-out thylakoid membranes isolated from the mutant could induce the formation of the 5.2-kD D1 C-terminal fragment, whereas the unrelated proteases trypsin and thermolysin could not. Immunoblot analysis revealed that mutants containing less Deg1 also contain less FtsH protease, and FtsH mutants contain less Deg1. These results suggest that Deg1 cooperates with the stroma-exposed proteases FtsH and Deg2 in degrading D1 protein during repair from photoinhibition by cleaving lumen-exposed regions of the protein. In addition, they suggest that accumulation of Deg1 and FtsH proteases may be coordinated.

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].…”

Role of Novel Dimeric Photosystem II (PSII)-Psb27 Protein Complex in PSII Repair

“…The resulting interstage repair complex is presumably similar to the CP43-less PSII complex RC47, which appears during biogenesis (14). The partial disassembly allows the removal of damaged D1, which is degraded mainly by FtsH protease in cyanobacteria, whereas in plants, several Deg proteases assist this process (15)(16)(17)(18). The new pD1 is cotranslationally synthesized into the D1-depleted PSII complex (19 -21), and the active holoenzyme is then reassembled similar to the biogenesis process.…”

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.…”

“…Initially Deg proteases, which are the other prokaryotic proteases found in cyanobacteria and higher plant chloroplasts, were the most promising protease candidate [31]. Through this and other related works, the D1 protein was suggested to be degraded first by Deg proteases [31], then further degraded by FtsH proteases [36,37]. The FtsH proteases were then suggested as the proteases responsible for the primary cleavage of the D1 protein [35,45].…”

“…In both photoinhibition and heat-inactivation, the protease systems work for swift repair of PSII in the thylakoid membrane, and also possibly in the stroma and in the thylakoid lumen [6]. Deg proteases and FtsH proteases are likely to be the proteases responsible for the degradation of the D1 protein [29, [31][32][33][34][35][36][37][38]. However, there are still many important questions to be answered in the degradation mechanism of the D1 protein.…”