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

Abstract

ORCID IDs: 0000-0002-2594-509X (S.S.M.); 0000-0001-6974-9587 (R.L.L.).Photosystem II (PSII) is a multiprotein complex that catalyzes the light-driven water-splitting reactions of oxygenic photosynthesis. Light absorption by PSII leads to the production of excited states and reactive oxygen species that can cause damage to this complex. Here, we describe Arabidopsis (Arabidopsis thaliana) At1g71500, which encodes a previously uncharacterized protein that is a PSII auxiliary core protein and hence is named PHOTOSYSTEM II PROTEIN33 (PSB33). We present evidence that PSB33 functions in the maintenance of PSII-light-harvesting complex II (LHCII) supercomplex organization. PSB33 encodes a protein with a chloroplast transit peptide and one transmembrane segment. In silico analysis of PSB33 revealed a light-harvesting complexbinding motif within the transmembrane segment and a large surface-exposed head domain. Biochemical analysis of PSII complexes further indicates that PSB33 is an integral membrane protein located in the vicinity of LHCII and the PSII CP43 reaction center protein. Phenotypic characterization of mutants lacking PSB33 revealed reduced amounts of PSII-LHCII supercomplexes, very low state transition, and a lower capacity for nonphotochemical quenching, leading to increased photosensitivity in the mutant plants under light stress. Taken together, these results suggest a role for PSB33 in regulating and optimizing photosynthesis in response to changing light levels.

Bioorthogonal Noncanonical Amino Acid Tagging (BONCAT) Enables Time-Resolved Analysis of Protein Synthesis in Native Plant Tissue

“…As sessile organisms, plants must retain a high degree of proteomic plasticity to enable rapid responses to a barrage of environmental cues (Huot et al, 2014;Fristedt et al, 2015;Mickelbart et al, 2015). In plants, as in most eukaryotes, mRNA abundance is often a poor proxy for protein levels (Ingolia, 2014;Vélez-Bermúdez and Schmidt, 2014;Fukao, 2015), as indicated by the discordance between total mRNA abundance and polyribosome-associated mRNAs under control and abiotic stress conditions (reviewed by Roy and von Arnim, 2013).…”

“…With advances in mass spectrometry-based peptide identification, new strategies have been developed to measure the extent to which protein levels are adjusted in response to environmental stimuli (Huot et al, 2014;Fristedt et al, 2015). But there are limitations to these technologies, which for the most part yield information about steady-state protein abundances.…”

A land plant‐specific thylakoid membrane protein contributes to photosystem II maintenance in Arabidopsis thaliana

“…This screen led to identification of LQY1 (Low Quantum Yield of PSII 1), a small thylakoid zinc finger protein that was shown to be involved in repair and reassembly of PSII (Lu, ; Lu et al ., ). The screen also identified PSB33, a recently described PSII‐associated thylakoid membrane protein that ensures proper maintenance of PSII/light‐harvesting complex II (LHCII) supercomplexes (Fristedt et al ., ).…”

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

“…The differential association of photosystems, LHCII, and other components of the thylakoid membrane gives rise to a set of supercomplexes that are central in ensuring photosynthetic efficiency and a rapid response to environmental cues (Caffarri et al, 2009;Duffy et al, 2013;Pietrzykowska et al, 2014;Fristedt et al, 2015). Fine tuning the dynamic assembly of these supercomplexes involves the association of antennae containing specific sets of Lhcb proteins.…”