Assembly of the D1 Precursor in Monomeric Photosystem II Reaction Center Precomplexes Precedes Chlorophyll a–Triggered Accumulation of Reaction Center II in Barley Etioplasts

Abstract

Assembly of plastid-encoded chlorophyll binding proteins of photosystem II (PSII) was studied in etiolated barley seedlings and isolated etioplasts and either the absence or presence of de novo chlorophyll synthesis. De novo assembly of reaction center complexes in etioplasts was characterized by immunological analysis of protein complexes solubilized from inner etioplast membranes and separated in sucrose density gradients. Previously characterized membrane protein complexes from chloroplasts were utilized as molecular mass standards for sucrose density gradient separation analysis. In etiolated seedlings, induction of chlorophyll a synthesis resulted in the accumulation of D1 in a dimeric PSII reaction center (RCII) complex. In isolated etioplasts, de novo chlorophyll a synthesis directed accumulation of D1 precursor in a monomeric RCII precomplex that also included D2 and cytochrome b 559 . Chlorophyll a synthesis that was chemically prolonged in darkness neither increased the yield of RCII monomers nor directed assembly of RCII dimers in etioplasts. We therefore conclude that in etioplasts, assembly of the D1 precursor in monomeric RCII precomplexes precedes chlorophyll a -triggered accumulation of reaction center monomers. INTRODUCTIONIn higher plants grown in darkness, formation of the photosynthetic apparatus is contingent on the light-dependent induction of chloroplast development. Light regulates synthesis of the chlorophyll a precursor protochlorophyllide a and is used as a substrate to enable the enzymatic re duction of protochlorophyllide a into chlorophyllide a by NADPH-protochlorophyllide oxidoreductase (POR) (von Wettstein et al., 1995;Fujita, 1996). The subsequent enzymatic esterification of chlorophyllide a to chlorophyll a has been found to be the decisive step for the accumulation of the chlorophyll a binding apoproteins P700A/P700B, CP47, CP43, and D1 of photosystems I and II (PSI and PSII), because binding of chlorophyll a to the apoproteins confers stability against proteolysis (Eichacker et al., 1996a). Similarly, other chlorophyll-associated proteins, including the nuclear-encoded chlorophyll a / b binding light-harvesting proteins (Bennett, 1981;Kuttkat et al., 1998), PSI chlorophyll proteins in Chlamydomonas (Herrin et al., 1992), and bacteriochlorophyll binding proteins of photosynthetic bacteria, are stabilized by chlorophyll (Dierstein, 1983). As shown indirectly by spectroscopy and by photochemical activity measurements, binding of chlorophyll a occurs within the first hour after illumination of etiolated barley (Egnéus et al., 1972;Wellburn and Hampp, 1979;Burkey, 1986;Ohashi et al., 1989;Franck, 1993); however, no direct evidence for chlorophyll a -dependent photosystem assembly has been reported.Chlorophyll a -dependent accumulation of plastidencoded chlorophyll a binding proteins is regulated at the cotranslational and post-translational levels (Klein and Mullet, 1986;van Wijk and Eichacker, 1996;Edhofer et al., 1998;Mühlbauer and Eichacker, 1998). During the first hour of illum...

Cool temperatures interfere with D1 synthesis in tomato by causing ribosomal pausing

“…When PSII is rendered inoperable, the PSII center migrates from the grana to the stroma lamellae where the damaged D1 is removed and the new protein inserted (Choquet and Vallon 2000). Studies of D1 synthesis in intact chloroplast translation systems (Zhang et al 1999) have demonstrated that D1 associates with a D2-cytochrome b559 complex during translation (Adir et al 1990;van Wijk et al 1997;Muller and Eichacker 1999;Zhang et al 1999), which is thought to stabilize the nascent protein. A previous study by Salonen et al (1998) also observed a decrease in the turnover of D1 in leaf discs of chilling-sensitive pumpkin exposed to low temperature and high light.…”

“…A recent study in Chlamydomonas reinhardtii identified initiation of translation as a main regulatory step in the biogenesis of the core proteins D1 and apoCP47 (Minai et al 2006). Repair of photodamaged reaction centers, however, is most likely regulated at elongation of translation (Kim et al 1994;Kettunen et al 1997;Minai et al 2006) as the reaction center core must be partially disassembled to allow the cotranslational insertion of D1 (Adir et al 1990;van Wijk et al 1997;Muller and Eichacker 1999;Zhang et al 1999). Cotranslational insertion explains why D1 is not found free in the membrane and is typically associated with at least D2 (Zhang et al 1999).…”

Defects in leaf carbohydrate metabolism compromise acclimation to high light and lead to a high chlorophyll fluorescence phenotype in Arabidopsis thaliana

“…In case of PSII photoinhibition, Cyt b 559 is degraded in parallel with the rest of the PSII reaction center [46]. However, free Cyt b 559 has for instance been observed in etioplasts prior to PSII assembly during de-etiolation [47,48] or in a screen for HCF mutants, particularly those affected in PSII [33]. It has recently been proposed that Cyt b 559 acts as a plastoquinole oxidase [49].…”

Proteomic analysis of highly purified prolamellar bodies reveals their significance in chloroplast development

“…Some of the proteins in the photosynthetic machinery, e.g. Hcf136 and the oxygenevolving complex, are of importance already at an early stage of chloroplast development, because of their roles in the correct assembly of the photosystems (Ryrie et al 1984;Hashimoto et al 1993;Müller and Eichacker 1999;Plücken et al 2002). The presence of chlorophyll is a prerequisite for the accumulation of most chlorophyll-binding proteins, e.g.…”