Inducible Repression of Nuclear-Encoded Subunits of the Cytochrome b6f Complex in Tobacco Reveals an Extraordinarily Long Lifetime of the Complex    

Abstract

The biogenesis of the cytochrome b6f complex in tobacco (Nicotiana tabacum) seems to be restricted to young leaves, suggesting a high lifetime of the complex. To directly determine its lifetime, we employed an ethanol-inducible RNA interference (RNAi) approach targeted against the essential nuclear-encoded Rieske protein (PetC) and the small M subunit (PetM), whose function in higher plants is unknown. Young expanding leaves of both PetM and PetC RNAi transformants bleached rapidly and developed necroses, while mature leaves, whose photosynthetic apparatus was fully assembled before RNAi induction, stayed green. In line with these phenotypes, cytochrome b6f complex accumulation and linear electron transport capacity were strongly repressed in young leaves of both RNAi transformants, showing that the M subunit is as essential for cytochrome b6f complex accumulation as the Rieske protein. In mature leaves, all photosynthetic parameters were indistinguishable from the wild type even after 14 d of induction. As RNAi repression of PetM and PetC was highly efficient in both young and mature leaves, these data indicate a lifetime of the cytochrome b6f complex of at least 1 week. The switch-off of cytochrome b6f complex biogenesis in mature leaves may represent part of the first dedicated step of the leaf senescence program.

Alternative oxidase: a respiratory electron transport chain pathway essential for maintaining photosynthetic performance during drought stress

“…Overall, the findings support the view that by contributing to R L during drought, AOX influences energy balance in the chloroplast, hence impacting both the PQ and NAD(P)H redox states. There is normally a strict co-regulation of the cyt b 6 f complex and ATP synthase amounts to balance the proton circuit, such that lumen acidification is sufficient to drive ATP synthesis, but without activating NPQ and photosynthetic control (Hojka et al 2014, Schöttler and. In WT tobacco, mild and moderate drought resulted in similar (and modest) declines in both cyt b 6 f and ATP synthase without generating any biochemical limitations of photosynthesis (Dahal et al 2015).…”

Photoprotection Conferred by Changes in Photosynthetic Protein Levels and Organization during Dehydration of a Homoiochlorophyllous Resurrection Plant

“…Thus, it seems that regulation of the cytochrome b 6 f complex to halt electron transport (both linear and cyclic) may be a global strategy in different organisms and at different stress conditions. It was recently shown that in mature tobacco (Nicotiana tabacum) leaves, the cytochrome b 6 f complex has a rather long lifetime (Hojka et al, 2014). It is interesting, therefore, that this complex is targeted for degradation earlier than other proteins of the photosynthetic apparatus, which have considerably shorter lifetimes.…”

A Nitrogen-Fixing Subunit Essential for Accumulating 4Fe-4S-Containing Photosystem I Core Proteins

“…Another example of classic 2Fe-2S-containing protein is glutaredoxin (GRX), which has a similar role to FD (Rouhier, 2010). The 2Fe-2S cluster in Cyt b 6 f is bound to photosynthetic electron transfer C (PetC), a Rieske ironsulfur protein (Hojka et al, 2014). Among the three 4Fe-4S clusters in PSI, one of them is referred to as F X and is associated with the PsaA/PsaB (where Psa stands for PSI) heterodimer, while the other two are referred to as F A and F B and are bound to PsaC (Saenger et al, 2002;Golbeck, 2003;Amann et al, 2004;Lezhneva et al, 2004).…”