FtsH facilitates proper biosynthesis of photosystem I in Arabidopsis thaliana

Abstract

Thylakoid membrane-bound FtsH proteases have a well-characterized role in degradation of the photosystem II (PSII) reaction center protein D1 upon repair of photodamaged PSII. Here, we show that the Arabidopsis (Arabidopsis thaliana) var1 and var2 mutants, devoid of the FtsH5 and FtsH2 proteins, respectively, are capable of normal D1 protein turnover under moderate growth light intensity. Instead, they both demonstrate a significant scarcity of PSI complexes. It is further shown that the reduced level of PSI does not result from accelerated photodamage of the PSI centers in var1 or var2 under moderate growth light intensity. On the contrary, radiolabeling experiments revealed impaired synthesis of the PsaA/B reaction center proteins of PSI, which was accompanied by the accumulation of PSI-specific assembly factors. psaA/B transcript accumulation and translation initiation, however, occurred in var1 and var2 mutants as in wild-type Arabidopsis, suggesting problems in later stages of PsaA/B protein expression in the two var mutants. Presumably, the thylakoid membrane-bound FtsH5 and FtsH2 have dual functions in the maintenance of photosynthetic complexes. In addition to their function as a protease in the degradation of the photodamaged D1 protein, they also are required, either directly or indirectly, for early assembly of the PSI complexes.

Structural and Functional Heat Stress Responses of Chloroplasts of Arabidopsis thaliana

“…The observed changes in protein abundance again are centered around PSI or PSII, which is consistent with the reduced photosynthetic performance of the mutant. However, we did not find PS components, but many regulatory factors with higher abundance (HHL1, RBD1, Lil3.1, Trx-m1, Cyp38, FNR, TROL, FTSH5; Figure 6 ; [ 72 , 73 , 74 , 75 , 85 , 89 , 90 , 91 , 92 ]). In toc64-1 , the five PS components with altered abundance are all reduced ( Figure 3 ; Table 1 ).…”

Folding-Degradation Relationship of a Membrane Protein Mediated by the Universally Conserved ATP-Dependent Protease FtsH

“…The substantial un-folding-dislocation ability discovered in this study will expand the range of potential substrates to: membrane proteins which are misfolded or aggregated with stable non-native interactions, membrane proteins which are folded but need to be degraded for regulatory purpose or toxicity, and prematurely truncated translation products which need to be immediately degraded from the membrane. Several pieces of evidence support the need and existence of significant unfoldase activity of FtsH in bacteria, mitochondria and chloroplasts: (1) FtsH rapidly degrades the whole SecYEG translocase complex jammed with an inefficiently secreted protein 67 ; (2) FtsH in the thylakoid membranes mediates swift regeneration of the damaged photosynthetic reaction center by degrading the photo-oxidized core proteins 9,68 ; (3) Chaperone activity of FtsH has been reported which requires active unfolding 69 . These quality control processes can be better understood by the FtsH activity redefined in this study.…”

FtsH Protease in the Thylakoid Membrane: Physiological Functions and the Regulation of Protease Activity

“…A later study in Chlamydomonas showed that the cytochrome b 6 f complex is degraded by FtsH in conditions of sulfur or nitrogen starvation, indicating that FtsH plays a role in protein quality control during nutrient deficiency ( Malnoë et al, 2014 ; Wei et al, 2014 ). On the other hand, Järvi and coworkers showed that FtsH functions in the biosynthesis of PSI ( Järvi et al, 2016 ). Furthermore, the low levels of FtsH in Arabidopsis ftsh mutants seem to affect the entire photosynthetic electron transfer chain.…”

“…Furthermore, the low levels of FtsH in Arabidopsis ftsh mutants seem to affect the entire photosynthetic electron transfer chain. Analysis of chlorophyll fluorescence implies that mutants lacking FtsH exhibit high rates of cyclic electron transfer around photosystem I (PSI), which results in a higher non-photochemical quenching value ( Järvi et al, 2016 ). Additionally, Chlamydomonas FtsH plays a role in degrading the light-harvesting chlorophyll a/b-binding proteins associated with PSI ( Bujaldon et al, 2017 ).…”