Deletion of PsbM in Tobacco Alters the QB Site Properties and the Electron Flow within Photosystem II

Abstract

Photosystem II, the oxygen-evolving complex of photosynthetic organisms, includes an intriguingly large number of low molecular weight polypeptides, including PsbM. Here we describe the first knock-out of psbM using a transplastomic, reverse genetics approach in a higher plant. Homoplastomic ⌬psbM plants exhibit photoautotrophic growth. Biochemical, biophysical, and immunological analyses demonstrate that PsbM is not required for biogenesis of higher order photosystem II complexes. However, photosystem II is highly light-sensitive, and its activity is significantly decreased in ⌬psbM, whereas kinetics of plastid protein synthesis, reassembly of photosystem II, and recovery of its activity are comparable with the wild type. Unlike wild type, phosphorylation of the reaction center proteins D1 and D2 is severely reduced, whereas the redox-controlled phosphorylation of photosystem II light-harvesting complex is reversely regulated in ⌬psbM plants because of accumulation of reduced plastoquinone in the dark and a limited photosystem II-mediated electron transport in the light. Charge recombination in ⌬psbM measured by thermoluminescence oscillations significantly differs from the 2/6 patterns in the wild type. A simulation program of thermoluminescence oscillations indicates a higher Q B /Q B ؊ ratio in dark-adapted mutant thylakoids relative to the wild type. The interaction of the Q A /Q B sites estimated by shifts in the maximal thermoluminescence emission temperature of the Q band, induced by binding of different herbicides to the Q B site, is changed indicating alteration of the activation energy for back electron flow. We conclude that PsbM is primarily involved in the interaction of the redox components important for the electron flow within, outward, and backward to photosystem II.

A photosynthesis operon in the chloroplast genome drives speciation in evening primroses

“…3b and below). Moreover, as judged from knockout mutants in tobacco, even complete loss of the PsbM protein does not lead to a strong phenotype that would be comparable to our material 45 . By contrast, petN encodes an essential subunit of the Cytb 6 f 46,47 , and reduced petN transcript stability, therefore, could affect Cytb 6 f accumulation.…”

Light-Induced Changes within Photosystem II Protects Microcoleus sp. in Biological Desert Sand Crusts against Excess Light

“…strain PCC 6803 (hereafter Synechocystis , Fig. 5A ), green algae and higher plants [27],[28] the maximal B bands emissions were detected at 30–35°C. The Q band obtained in the presence of various herbicides that block electron flow via the Q B site occurs at significantly lower temperatures in higher plants [28].…”

“…5A ), green algae and higher plants [27],[28] the maximal B bands emissions were detected at 30–35°C. The Q band obtained in the presence of various herbicides that block electron flow via the Q B site occurs at significantly lower temperatures in higher plants [28]. The Q band of cyanobacteria such as Synechocystis occurs at 17°C or 12°C in the presence of DCMU or ioxynil, respectively ( Fig.…”

Photoinactivation of photosystem II: is there more than one way to skin a cat?

“…Notably, the extent, order and specificity of processes exhibited by a certain ‘model organism’ may differ from those examined here, reflecting acclimation to various conditions. In this respect, it is important to consider the function of the LMW proteins, 2–6 kDa range (Ohad et al 2004, Regel et al 2001, Schwenkert et al 2006, Swiatek et al 2003, Umate et al 2007, 2008). The contribution of these proteins to the electron transfer regulation under light stress and PI is poorly understood but deletion of the relevant genes results in significant changes in the electron transfer activity of PSII (Fig.…”

“…Values for the disruption mutants are relative to the wild type. For experimental details refer to Regel et al (2001), Swiatek et al (2003), Ohad et al (2004), Schwenkert et al (2006) and Umate et al (2007, 2008).…”