Light-dependent dynamics of phosphorylation of the thylakoid structural protein CURT1B

ABSTRACT: The regulation of the photosynthetic apparatus in higher plants is highly connected to the organization of the thylakoid membrane into appressed and non-appressed regions. The two photosystems (I and II) are the spatially strongest segregated protein complexes by this thylakoid heterogenous organization, with PSII predominantly present in the appressed membranes (grana), while PSI is confined to the stroma-exposed non-appressed thylakoid membranes (lamellae). Stacking of thylakoid membranes in grana is highly dynamic and influenced by the levels of PSII and LHCII protein phosphorylation which, in turn, are dependent on changes in light intensity and quality and thus, ultimately, on the redox state of the electron transfer chain. Dynamics of this lateral heterogeneity controls the spillover of excitation energy from PSII to PSI and optimizes the photochemistry in constantly fluctuating light conditions. Recently, a family of membrane-integral thylakoid proteins named CURVATURE THYLAKOID 1 (CURT1) have been proposed as new key components in shaping both the width and the number of layers per granum in response to changes in light intensity. CURT1B, in particular, has been known for a long time as a relatively abundant phosphorylated and acetylated protein, but so far the role and dynamics of these post-translational modifications (PTMs) have not been revealed. To this end, we have quantified by means of targeted proteomics the amount of CURT1 proteins and the level of CURT1B PTMs after short-term fluctuating light treatments in wild type Arabidopsis thaliana and the knock-out mutants of the kinases STN7 and STN8 and of the phosphatase TAP38. The CURT1B protein was first localized to a specific curvature domain largely depleted of the chlorophyll-protein complexes. Moreover, we have found that CURT1B is either phosphorylated or acetylated in the N-terminus, but never both. While the level of acetylation is never affected by the light treatments, the phosphorylation increases in light conditions that lead to sudden increase in PSII core protein phosphorylation, and these dynamics are largely abolished in stn8 plants but not in stn7 or tap38. Intriguingly, the phosphorylation dynamics as well as the level of the other CURT1 proteins, are instead highly affected in psb33 plants, which lack LHCII phosphorylation dynamics, and in the psal plants, which show constitutively phosphorylated LHCII. These results provide important information for assessing the relationships between PSII-LHCII phosphorylation, CURT1B phosphorylation and the dynamics of the appressed thylakoids, which in turn allow optimal photosynthesis and provide photoprotection under fluctuations in light intensity.

ORGANISM(S): Arabidopsis Thaliana

SUBMITTER: Andrea Trotta  

PROVIDER: PXD014562 | panorama | Fri Nov 01 00:00:00 GMT 2019

REPOSITORIES: PanoramaPublic