PSB33 sustains Photosystem II D1 protein under fluctuating light conditions
- Organism: Arabidopsis thaliana Col-0
- Instrument: TSQ vantage Thermo Scientific
On Earth, solar irradiance varies as the sun rises and sets over the horizon, sunlight is thus in constant fluctuation, following a slow dark-low-high-low-dark curve. Optimal plant growth and development are dependent on the capacity of plants to acclimate and regulate photosynthesis in response to these changes of light. Little is known of regulative processes for photosynthesis during nocturnal events. The nucleus-encoded plant lineage-specific protein PSB33 has been described to stabilize the Photosystem II complex, especially under light stress conditions, and plants lacking PSB33 have a dysfunctional state transition. To clarify the localization and function of this protein, we used phenomic, biochemical and proteomics approaches. We report that PSB33 is predominantly located in non-appressed thylakoid regions and dynamically associates with a thylakoid protein complex in a light-dependent manner. Moreover, under nocturnal periods, plants lacking PSB33 show an accelerated D1 protein degradation, and severely stunted growth when challenged with fluctuating light. We further show that the function of PSB33 precedes the STN7 kinase to regulate/balance the excitation energy of Photosystems I and II in fluctuating light conditions.
Quantification of the ratio between thylakoids membrane proteins Photosysthem II (PSII), Cytochrome b6f (Cyt b6f) and Photosystem I (PSI) and the kinases STN7 and STN8, the phosphatase TAP38, the proteins PSB33, LHCB1 and LHCB2. Three unique proteotypic peptides from two subunits of PSII (D2 and CP47), PSI (PsaA and PsaB) and Cyt b6f (CytF and CytB6) and from STN7, STN8, TAP38, PSB33, and three shared peptide of LHCB1 and LHCB2 were used to calculate the ratios between the three thylakoid complexes and between the complexes and the abovementioned proteins. Whole thylakoids were denatured in 6M urea 6% acrylamide SDS-PAGE and in-gel digested with trypsin. The peptide mixture has been first analyzed in DDA and the MS/MS acquired utilized to generate the SRM transitions. The sum of the intensities (integrated peak area) of the three most intense transition for every peptide have been utilized to calculate the ratio between protein complexes and targeted proteins.
The ratios have been calculated using wild-type and psb33 knocked-out mutant thylakoid proteins isolated from plants treated with a fluctuating light cycle of 16 hours of Dark, followed by 2 hours of low light, then 2 hours of high light and finally again 2 hours of low light.
Created on 5/3/17, 11:38 AM