The category of PSII photoinhibition
The amplitude L 1 of the DF decay kinetics component declined significantly during the initial illumination already and continuously decreased with exposure duration (Fig. 1A), suggesting the decreased electron transport capacity of the PSII donor side following light exposure. As shown in Fig. 1B and C, the relative variable fluorescence at the K-step (W K) was significantly increased and OEC peripheral proteins including the manganese-stabilizing protein PsbO and the Ca2+-binding protein PsbP were significantly downregulated, confirming the partial impairment of OEC during the initial illumination. This decrease of OEC activity was accompanied by the decrease of PSII photochemical activity characterized by the decrease of F Pfollowing light exposure (Fig. 1D). In the presence of lincomycin inhibiting D1 protein synthesis, the time-course changes inF v/F m under various photosynthetic photon flux density (PPFD) values fitted the first-order kinetics well (Fig. 1E). Both the decreased F v/F meven under ultra-dim light during the initial illumination and the direct proportionality of KPI to PPFD from dim light to supersaturating light intensities further supported the occurrence of PSII donor-side photoinhibition in Z. marina(Fig. 1F).
Overview of quantitative proteome analysis
Among 2613 protein groups, a total of 2187 proteins were quantified with at least one unique peptide sequence (Fig. S1A). Z. marinasamples were clustered and distinguished from each other based on light treatment (Fig. S1B). The 127 differentially expressed proteins (DEPs) were determined, which included 89 upregulated proteins and 38 downregulated proteins (Fig. S1C). Based on Gene ontology (GO) enrichment analysis, DEPs were classified into the following several biological processes: “photosystem II assembly”, “chlorophyll biosynthetic process”, “photosynthetic electron transport in photosystem I”, “regulation of photosynthesis, light reaction”, “PSII associated light-harvesting complex II catabolic process”, “response to light intensity”, and so on (Fig. 2A). In the Protein-protein interaction (PPI) network of the DEPs, OEC peripheral protein PsbO had a high degree of connectivity and strong interactions with other proteins (Fig. 2B), indicating that thte photoinactivated OEC played a central role in the photosynthetic regulation of Z. marina .