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 .