Lack of the Small Plastid-encoded PsbJ Polypeptide Results in a Defective Water-splitting Apparatus of Photosystem II, Reduced Photosystem I Levels, and Hypersensitivity to Light

Abstract

Photosystem II is a large pigment-protein complex catalyzing water oxidation and initiating electron transfer processes across the thylakoid membrane. In addition to large protein subunits, many of which bind redox cofactors, photosystem II particles contain a number of low molecular weight polypeptides whose function is only poorly defined. Here we have investigated the function of one of the smallest polypeptides in photosystem II, PsbJ. Using a reverse genetics approach, we have inactivated the psbJ gene in the tobacco chloroplast genome. We show that, although the PsbJ polypeptide is not principally required for functional photosynthetic electron transport, plants lacking PsbJ are unable to grow photoautotrophically. We provide evidence that this is due to the accumulation of incompletely assembled water-splitting complexes, which in turn causes drastically reduced photosynthetic performance and extreme hypersensitivity to light. Our results suggest a role of PsbJ for the stable assembly of the water-splitting complex of photosystem II and, in addition, support a control of photosystem I accumulation through photosystem II activity. Photosystem II (PSII)1 is a large cofactor-protein complex consisting of at least 17 protein subunits (Ref. 1; for review, see e.g. Ref. 2). The PSII reaction center is formed by a heterodimer of two pigment-binding proteins, D1 and D2, which, in photosynthetic eukaryotes, are encoded by the chloroplast psbA and psbD genes, respectively. The photochemical reaction carried out by the reaction center converts the energy of a photon into a separation of charge and, in this way, initiates electron flow. Around the reaction center, the outer parts of PSII are assembled, the inner and outer antennae funneling absorbed light energy to the catalytic core and the oxygen-evolving complex splitting water into protons, electrons, and dioxygen (reviewed in Refs. 3 and 4).In addition to the well-studied large protein subunits, purified PSII particles contain a number of low molecular weight polypeptides, many of which are encoded by the plastid genome of photosynthetically active eukaryotes (5). Most of these small subunits do not bind redox cofactors and, hence, are unlikely to participate directly in electron transfer reactions. It is generally assumed that they rather function as photosystem-assembling or stabilizing factors. However, in many cases, molecular evidence supporting such a structural role is largely lacking. The successful development of transformation technologies for Chlamydomonas (6) and tobacco chloroplasts (7) has paved the way to functional characterizations of plastid genome-encoded genes by reverse genetics. Linked to a selectable marker gene, mutant alleles can be introduced into plastids by chloroplast transformation, where they replace the endogenous wildtype allele by homologous recombination. During the past decade, reverse genetics has become a powerful tool in plastid functional genomics (reviewed in Ref. 8).Here, we have taken a reverse genetics approach to def...

The Conserved His-144 in the PsbP Protein Is Important for the Interaction between the PsbP N-terminus and the Cyt b559 Subunit of Photosystem II

“…Transplastomic tobacco plants that have a mutation in PsbE showed lower associations between PsbP and PSII in the thylakoid membranes (45). It was reported that PsbJ in the vicinity of Cyt b 559 is required for the association of PsbP with PSII and the assembly of PsbR in tobacco (35,46), and that PsbR is required for the stable binding of PsbP and PsbQ in Arabidopsis (36). In addition, we observed a putative cross-linking between PsbR and PsbE (Fig.…”

PsbR, a Missing Link in the Assembly of the Oxygen-evolving Complex of Plant Photosystem II

“…Moreover, another LMM protein PsbJ is, in turn, required for the assembly of the PsbR protein, thus explaining the earlier reported importance of PsbJ for the assembly of PsbP (11,12). An interesting adaptation to constant low light conditions was detected; in WT plants, the OEC proteins PsbP and PsbQ as well as PsbR were up-regulated, whereas the PsbO amounts were not dependent on light intensity.…”

“…The 23-and 17-kDa OEC proteins PsbP and PsbQ have been found to associate with PSII only in the grana thylakoids (9). Moreover, the low molecular mass (LMM) PSII core protein PsbJ was recently reported to be a prerequisite for the association of PsbP with the PSII core (11,12). It has been suggested that PsbO provides a docking site for PsbP, and both PsbO and PsbP together are needed for the binding of PsbQ (13,14).…”

“…PsbJ is a representative example of such proteins. In cyanobacteria, the deletion of PsbJ allows slow photoautotrophic growth, whereas in tobacco plants, the corresponding deletion leads to a complete heterotrophy (11,12,(17)(18)(19). Moreover, higher plant PSII contains the nuclear-encoded LMM subunits PsbW and PsbR, which are completely lacking from cyanobacterial PSII.…”

Fotosíntesis y rendimiento de biomasa en ají, rábano y maíz sometidos a agua tratada magnéticamente

“…Además, previamente se ha informado que un deterioro o una promoción en el proceso de escisión del agua en el PSII deberían notarse en el rendimiento de la fluorescencia. Por ejemplo, en plantas mutantes de tabaco que carecen de un polipéptido específico en su aparato de escisión de agua en el PSII, exhiben valores de fluorescencia mínima (F 0 ) más altos y de fluorescencia variable (Fv) casi equivalentes a cero (Hager, Hermann, Biehler, Krieger-Liszkay, & Bock, 2002). Dado que no se observaron diferencias significativas entre el control y las plantas tratadas en los parámetros de fluorescencia, este estudio sugiere que el ATM no es metabólicamente susceptible a una división diferencial en el complejo oxidante del H2O.…”