The Variegated Mutants Lacking Chloroplastic FtsHs Are Defective in D1 Degradation and Accumulate Reactive Oxygen Species

Abstract

In the photosynthetic apparatus, a major target of photodamage is the D1 reaction center protein of photosystem II (PSII). Photosynthetic organisms have developed a PSII repair cycle in which photodamaged D1 is selectively degraded. A thylakoid membrane-bound metalloprotease, FtsH, was shown to play a critical role in this process. Here, the effect of FtsHs in D1 degradation was investigated in Arabidopsis (Arabidopsis thaliana) mutants lacking FtsH2 (yellow variegated2 [var2]) or FtsH5 (var1). Because these mutants are characterized by variegated leaves that sometimes complicate biochemical studies, we employed another mutation, fu-gaeri1 (fug1), that suppresses leaf variegation in var1 and var2 to examine D1 degradation. Twodimensional blue native PAGE showed that var2 has less PSII supercomplex and more PSII intermediate lacking CP43, termed RC47, than the wild type under normal growth light. Moreover, our histochemical and quantitative analyses revealed that chloroplasts in var2 accumulate significant levels of reactive oxygen species, such as superoxide radical and hydrogen peroxide. These results indicate that the lack of FtsH2 leads to impaired D1 degradation at the step of RC47 formation in PSII repair and to photooxidative stress even under nonphotoinhibitory conditions. Our in vivo D1 degradation assays, carried out by nonvariegated var2 fug1 and var1 fug1 leaves, demonstrated that D1 degradation was impaired in different light conditions. Taken together, our results suggest the important role of chloroplastic FtsHs, which was not precisely examined in vivo. Attenuated D1 degradation in the nonvariegated mutants also suggests that leaf variegation seems to be independent of the PSII repair.

Singlet oxygen- and EXECUTER1-mediated signaling is initiated in grana margins and depends on the protease FtsH2

“…The repair cycle is primarily designed for the specific replacement of D1, which requires the disassembly and reassembly of PSII complexes and depends on rapid protein translocation between grana core, grana margin, and stroma lamella (15). Damaged D1 is proteolytically cleaved by the FtsH protease (18,19). As most of the FtsH is found in grana margins (15,17), this part of the grana stacks seems to be a main site of protein degradation (15).…”

The Phosphorylation Status of the Chloroplast Protein Kinase STN7 of Arabidopsis Affects Its Turnover

“…We examined several available Arabidopsis mutant lines deficient in the chloroplast proteases FtsH2, FtsH5 (Kato et al, 2009), Deg2 (Huesgen et al, 2006), Deg5, Deg8 (Sun et al, 2007), and ClpR1 (Stanne et al, 2009) after a shift from blue light to far-red light. Some of these proteases act on the stromal side of the thylakoid membrane while others act on the lumen side or in the stroma.…”

Regulation of the photosynthetic apparatus under fluctuating growth light

“…on two topics: photoinhibition mechanisms and the repair cycle of PSII [11], and the strategies used by the photosynthetic machinery for dissipation of excess energy before it can enter the PSII reaction centre [12]. This somewhat limited focus may stem from the common perception that PSII damage must be repaired in order to prevent accumulation of radicals generated by chlorophyll molecules in damaged PSII and its light-harvesting antenna [13].The Sakamoto group has indeed shown an accumulation of ROS in a mutant with delayed degradation of PSII under high light [14], but the mechanism used by damaged PSII for donating electrons to molecular oxygen to generate the ROS seen in these mutants remains unknown. It could in fact be postulated that electrons accumulated in the electron transfer chain (ETC) under high light exceed the capacity of PSI electron acceptors and lead to ROS production by PSI in a classical way [15].…”