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The High Light Response and Redox Control of Thylakoid FtsH Protease in Chlamydomonas Reinhardtii

Abstract

In Chlamydomonas reinhardtii, the major protease involved in the maintenance of photosynthetic machinery in thylakoidmembranes,the FtsHprotease, mostlyforms large hetero-oligomers (1 MDa) comprising FtsH1 and FtsH2 subunits, whatever the light intensity for growth. Upon high light exposure, the FtsH subunits

display a shorter half-life, which is counterbalanced by an increase in

FTSH1/2 mRNA levels, resulting in the modest upregulation of FtsH1/2 proteins. Furthermore, we found that high light increases the protease activity through a hitherto unnoticed redox-controlled reduction of intermolecular disulfide bridges. We iso- lated a Chlamydomonas FTSH1 promoter-deficient mutant, ftsh1-3, resulting from the insertion of a TOC1 transposon, in which the high light-induced upregulation of FTSH1 gene expression is largely lost. In ftsh1-3, the abundance of FtsH1 and FtsH2 proteins are loosely coupled (decreased by 70% and 30%, respectively) with no formation of large and stable homo-oligomers. Using strains exhibiting different accumulation levels of the FtsH1 subunit after complementation of ftsh1-3, we demonstrate that high light tolerance is tightly

correlated with the abundance of the FtsH protease. Thus, the response of Chlamydomonas to light stress involveshigherlevelsofFtsH1/2subunitsassociatedintolargecomplexeswithincreasedproteolyticactivity.

Key words:

chloroplast protease, regulation of gene expression, photoinhibition,

Chlamydomonas reinhardtii

Wang F., Qi Y., Malnoe

̈

A., Choquet Y., Wollman F.-A., and de Vitry C.(2017). The High Light Response and Redox Control of Thylakoid FtsH Protease in

Chlamydomonas reinhardtii. Mol. Plant.10, 99–114.

Publié le : 02/08/2017

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