Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis

Abstract

Reversible protein phosphorylation plays a major role in the acclimation of the photosynthetic apparatus to changes in light. Two paralogous kinases phosphorylate subsets of thylakoid membrane proteins. STATE TRANSITION7 (STN7) phosphorylates LHCII, the light-harvesting antenna of photosystem II (PSII), to balance the activity of the two photosystems through state transitions. STN8, which is mainly involved in phosphorylation of PSII core subunits, influences folding of the thylakoid membranes and repair of PSII after photodamage. The rapid reversibility of these acclimatory responses requires the action of protein phosphatases. In a reverse genetic screen, we identified the chloroplast PP2C phosphatase, PHOTOSYSTEM II CORE PHOSPHATASE (PBCP), which is required for efficient dephosphorylation of PSII proteins. Its targets, identified by immunoblotting and mass spectrometry, largely coincide with those of the kinase STN8. The recombinant phosphatase is active in vitro on a synthetic substrate or on isolated thylakoids. Thylakoid folding is affected in the absence of PBCP, while its overexpression alters the kinetics of state transitions. PBCP and STN8 form an antagonistic kinase and phosphatase pair whose substrate specificity and physiological functions are distinct from those of STN7 and the counteracting phosphatase PROTEIN PHOSPHATASE1/ THYLAKOID-ASSOCIATED PHOSPHATASE38, but their activities may overlap to some degree.

PHOTOSYSTEM II PROTEIN33, a Protein Conserved in the Plastid Lineage, Is Associated with the Chloroplast Thylakoid Membrane and Provides Stability to Photosystem II Supercomplexes in Arabidopsis

“…redistribution of LHCII between the two photosystems; Lunde et al, 2000;Depège et al, 2003;Shapiguzov et al, 2010;Tikkanen et al, 2011). The state transition processes are influenced by the phosphorylation and dephosphorylation of various PSII proteins and the trimeric LHC (Fristedt and Vener, 2011;Samol et al, 2012). The thylakoid Ser/Thr-protein kinases STN7 and STN8, which phosphorylate LHCII and PSII, respectively, were shown previously to be activated by a reduced plastoquinone pool (Samol et al, 2012).…”

“…The state transition processes are influenced by the phosphorylation and dephosphorylation of various PSII proteins and the trimeric LHC (Fristedt and Vener, 2011;Samol et al, 2012). The thylakoid Ser/Thr-protein kinases STN7 and STN8, which phosphorylate LHCII and PSII, respectively, were shown previously to be activated by a reduced plastoquinone pool (Samol et al, 2012). We measured the phosphorylation status of the thylakoid membrane proteins LHCII, D1, D2, and CP43 in plants acclimated to dark, 120 PPFD, and 800 PPFD (Supplemental Fig.…”

Chloroplast Proteases: Updates on Proteolysis within and across Suborganellar Compartments

“…The PSII core proteins D1, D2, CP43, and PsbH can be phosphorylated; the phosphorylation sites are all located in their stroma-facing N termini (Puthiyaveetil and Kirchhoff, 2013). The phosphorylation and dephosphorylation of these proteins require the thylakoid-associated Ser/Thr kinase STATE TRANSITION8 (STN8; Bonardi et al, 2005) and the stroma/thylakoid-localized PROTEIN PHOSPHATASE 2C-TYPE PSII CORE PHOSPHA-TASE (PBCP; Samol et al, 2012). Lack of STN8 results in enhanced Deg-dependent D1 fragmentation under high-light conditions (Kato and Sakamoto, 2014), whereas PBCP defects cause delayed D1 degradation in high light (Samol et al, 2012).…”

Phosphorylation of the Lhcb2 isoform of Light Harvesting Complex II is central to state transitions

“…Total protein extract from seedlings or leaves was prepared as previously described (Samol et al, 2012). The total protein concentration was measured with bicinchoninic acid solution (Sigma-Aldrich) following the manufacturer's instructions.…”