The Role of Phosphorylation in Redox Regulation of Photosynthesis Genes psaA and psbA during Photosynthetic Acclimation of Mustard

Abstract

The long-term response (LTR) to light-quality gradients improves performance and survival of plants in dense stands. It involves redox-controlled transcriptional regulation of the plastome-encoded genes psaAB (encoding the P700 apoproteins of photosystem I) and psbA (encoding the D1 protein of photosystem II) and requires the action of plastid-localized kinases. To study the potential impact of phosphorylation events on plastid gene expression during the LTR, we analyzed mustard seedlings acclimated to light sources favoring either photosystem I or photosystem II. Primer extension analyses of psaA transcripts indicate that the redox regulation occurs at the principal bacterial promoters, suggesting that the plastid encoded RNA polymerase (PEP) is the target for redox signals. Chloroplast protein fractions containing PEP and other DNA-binding proteins were purified from mustard via heparin-Sepharose chromatography. The biochemical properties of these fractions were analyzed with special emphasis on promoter recognition and specificity, phosphorylation state, and kinase activity. The results demonstrate that the LTR involves the action of small DNA-binding proteins; three of them exhibit specific changes in the phosphorylation state. Auto-phosphorylation assays, in addition, exhibit large differences in the activity of endogenous kinase activities. Chloroplast run-on transcription experiments with the kinase inhibitor H7 and the reductant DTT indicate that phosphorylation events are essential for the mediation of redox signals toward psaA and psbA transcription initiation, but require the synergistic action of a thiol redox signal. The data support the idea that redox signals from the thylakoid membrane are linked to gene expression via phosphorylation events; however, this mediation appears to require a complex network of interacting proteins rather than a simple phosphorelay.

Plastidial Thioredoxin z Interacts with Two Fructokinase-Like Proteins in a Thiol-Dependent Manner: Evidence for an Essential Role in Chloroplast Development in Arabidopsis and Nicotiana benthamiana

“…Arabidopsis CSK knockout mutants display a severe disturbance in psaA transcript accumulation during the photosystem stoichiometry adjustment, indicating that CSK is essential for proper redox regulation of psaA transcription, although the CSK target proteins yet remain elusive. However, recent evidence suggests that redox regulation of psaA and psbA transcription involves thiol modification acting synergistically with phosphorylation (Steiner et al, 2009), implicating a role for TRXs in this process. TRX z could thus play a role in mediating redox signals in photosystem stoichiometry adjustment as a long-term response to fluctuating light conditions.…”

Gene expression changes in response to drought stress in Ilex paraguariensis leaves

“…When tissue dehydration became more severe (Ψ soil = -3 MPa), the transcription of B9 sequences encoding Photosystem I P700 apoprotein A1 significantly decreased. Part of the long-term response to excitation imbalances between photosystems involves a readjustment of photosystem stoichiometry to keep the net energy fixation as high as possible (Steiner et al, 2009). In conjunction with the decrease of stomatal conductance, the expression of the F9 sequence encoding ribulose 1,5-bisphosphate carboxylase/oxygenase activase decreased in response to moderate and severe stress.…”

Dynamic Plastid Redox Signals Integrate Gene Expression and Metabolism to Induce Distinct Metabolic States in Photosynthetic Acclimation inArabidopsis

“…Determining if this binary redox control mode is really functional requires further experimental confirmation, including direct determination of thioredoxin redox states. However, cooperative redox signaling is not an unknown phenomenon since it has been proposed earlier to regulate translation initiation of the psbA gene in Chlamydomonas, activity of the LHCII kinase, and chloroplast gene expression in plants (Rintamaki et al, 2000;Trebitsh et al, 2000;Trebitsh and Danon, 2001;Hou et al, 2002;Pfannschmidt and Liere, 2005;Rochaix, 2007;Lemeille et al, 2009;Steiner et al, 2009).…”