Comparative analysis of thylakoid protein complexes in state transition mutants nsi and stn7: focus on PSI and LHCII

Abstract

The photosynthetic machinery of plants can acclimate to changes in light conditions by balancing light-harvesting between the two photosystems (PS). This acclimation response is induced by the change in the redox state of the plastoquinone pool, which triggers state transitions through activation of the STN7 kinase and subsequent phosphorylation of light-harvesting complex II (LHCII) proteins. Phosphorylation of LHCII results in its association with PSI (state 2), whereas dephosphorylation restores energy allocation to PSII (state 1). In addition to state transition regulation by phosphorylation, we have recently discovered that plants lacking the chloroplast acetyltransferase NSI are also locked in state 1, even though they possess normal LHCII phosphorylation. This defect may result from decreased lysine acetylation of several chloroplast proteins. Here, we compared the composition of wild type (wt), stn7 and nsi thylakoid protein complexes involved in state transitions separated by Blue Native gel electrophoresis. Protein complex composition and relative protein abundances were determined by LC-MS/MS analyses using iBAQ quantification. We show that despite obvious mechanistic differences leading to defects in state transitions, no major differences were detected in the composition of PSI and LHCII between the mutants. Moreover, both stn7 and nsi plants show retarded growth and decreased PSII capacity under fluctuating light as compared to wt, while the induction of non-photochemical quenching under fluctuating light was much lower in both nsi mutants than in stn7.

Quantitative proteomic analysis to capture the role of heat‐accumulated proteins in moss plant acquired thermotolerance

“…A near equimolar stoichiometry was also found within the photosystem I core between P700 chlorophyll apoprotein A1 and A2 (PsaA and PsaB) (Figure 2c,d ). Noticeably, PSII reaction centres were 3–4 times more abundant than PSI reaction centres, as reported earlier to be the case for higher plant chloroplasts (Jia, Ito, & Tanaka, 2016 ; Koskela et al, 2020 ). This highlights the potential for this data to be used as a basis for further functional exploration of complex enzymatic processes that require knowledge of enzyme abundances and stoichiometries, possibly at the systems biology scale.…”

Dynamic Changes in Protein-Membrane Association for Regulating Photosynthetic Electron Transport

“…This is consistent with STN7 and phosphorylated Lhcb2 being more abundant in stroma lamellae, whereas STN8 and phosphorylated Lhcb1 locate preferentially in the grana core [ 61 ]. Recently, Koskela and coworkers [ 62 , 63 ] discovered that phosphorylation of LHCII is not sufficient to induce its migration alone. Plants lacking the acetyltransferase NUCLEAR SHUTTLE INTERACTING (NSI) are locked in state 1, despite phosphorylation of LHCII.…”

Indirect Export of Reducing Equivalents From the Chloroplast to Resupply NADP for C3 Photosynthesis—Growing Importance for Stromal NAD(H)?

“…This situation supports CEF and overall protects PSI (Minagawa, 2011 ). Additionally, it was shown in Arabidopsis that acetylation of several photosynthesis components via the acetyltransferase NSI/ GNAT2 is also required for state transitions (Koskela et al, 2018 , 2020 ).…”