Thylakoid Membrane Maturation and PSII Activation Are Linked in Greening Synechocystis sp. PCC 6803 Cells

Abstract

Thylakoid membranes are typical and essential features of both chloroplasts and cyanobacteria. While they are crucial for phototrophic growth of cyanobacterial cells, biogenesis of thylakoid membranes is not well understood yet. Dark-grown Synechocystis sp. PCC 6803 cells contain only rudimentary thylakoid membranes but still a relatively high amount of phycobilisomes, inactive photosystem II and active photosystem I centers. After shifting dark-grown Synechocystis sp. PCC 6803 cells into the light, “greening” of Synechocystis sp. PCC 6803 cells, i.e. thylakoid membrane formation and recovery of photosynthetic electron transport reactions, was monitored. Complete restoration of a typical thylakoid membrane system was observed within 24 hours after an initial lag phase of 6 to 8 hours. Furthermore, activation of photosystem II complexes and restoration of a functional photosynthetic electron transport chain appears to be linked to the biogenesis of organized thylakoid membrane pairs.

The Proteome and Lipidome of Synechocystis sp. PCC 6803 Cells Grown under Light-Activated Heterotrophic Conditions*

“…For none of these subunits a significant change was observed, which is in line with the recent observation that LAHG cells have fully functional PS I centers (15). Only the PS I assembly factor BtpA (Sll0634) (67) was increased 18-fold under LAHG conditions, whereas the content of other quantified PS I assembly factors, such as Ycf3 (67) or Ycf37 (68), was not altered.…”

“…The quantity of pigment binding subunits of the light-harvesting phycobilisomes, which are the most abundant proteins in cyanobacteria, had not significantly changed, in line with recent observations (15). However, the abundance of linker…”

“…In line with this assumption, an increased fluorescence emission, caused by uncoupled phycobilisome proteins, was recently observed in LAHG-grown Synechocystis cells upon phycobilisome excitation (15).…”

“…The chlorophyll content per cell dramatically decreases (15), and severe reduction of pigment-binding protein complexes is one of the most prominent phenotype associated with LAHG conditions. In contrast, the cellular concentration of the pigment binding subunits of the soluble light-harvesting phycobilisomes is not decreased, as revealed by former spectroscopic analysis (15). Only LAHG cells having these characteristics were harvested and fractionated for subsequent analyses.…”

“…The ability of Synechocystis to grow under LAHG conditions has been used recently to analyze TM formation within cyanobacterial cells (15). Although darkadapted Synechocystis cells have no active PS II complex, complete photosynthetic activity is regained within 24 h after transferring dark-adapted cells into the light.…”