A critical role for the Var2 FtsH homologue of Arabidopsis thaliana in the photosystem II repair cycle in vivo.
Using a var2-2 mutant of Arabidopsis thaliana, which lacks a homologue of the zinc-metalloprotease, FtsH, we demonstrate that this protease is required for the efficient turnover of the D1 polypeptide of photosystem II and protection against photoinhibition in vivo. We show that var2-2 leaves are much more susceptible to light-induced photosystem II photoinhibition than wild-type leaves. Furthermore, the rate of photosystem II photoinhibition in untreated var2-2 leaves is equivalent to that of var2-2 and wild-type leaves, which have been treated with lincomycin, an inhibitor of the photosystem II repair cycle at the level of D1 synthesis. This is in contrast to untreated wild-type leaves, which show a much slower rate of photosystem II photoinhibition due to an efficient photosystem II repair cycle. The recovery of var2-2 leaves from photosystem II photoinhibition is also impaired relative to wild-type. Using Western blot analysis in the presence of lincomycin we show that the D1 polypeptide remains stable in leaves of the var2-2 mutant under photoinhibitory conditions that lead to D1 degradation in wild-type leaves and that the abundance of DegP2 is not affected by the var2-2 mutation. We conclude, therefore, that the Var2 FtsH homologue is required for the cleavage of the D1 polypeptide in vivo. In addition, we identify a conserved lumenal domain in Var2 that is unique to FtsH homologues from oxygenic phototrophs.
Bailey
Shaun
S
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, London WC1E 6BT, United Kingdom.
Thompson
Elinor
E
Nixon
Peter J
PJ
Horton
Peter
P
Mullineaux
Conrad W
CW
Robinson
Colin
C
Mann
Nicholas H
NH
D049069:ATP-Dependent Proteases; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins; D001426:Bacterial Proteins / Q000502:physiology*; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D008027:Light; D008034:Lincomycin / Q000494:pharmacology; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000037:antagonists & inhibitors / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence
D049069:ATP-Dependent Proteases; D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D008034:Lincomycin; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C402651:AT2G30950 protein, Arabidopsis