Cloning and Expression of the Soybean chlH Gene Encoding a Subunit of Mg-Chelatase and Localization of the Mg2+ Concentration-Dependent ChlH Protein within the Chloroplast

Nakayama, Masato; Masuda, Tatsuru; Bando, Tsuyosbi; Yamagata, Hiroshi; Ohta, Hiroyuki; Takamiya, Ken-ichiro

doi:10.1093/oxfordjournals.pcp.a029368

Cited by 83 publications

(49 citation statements)

References 31 publications

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“…Under circadian conditions, however, magnesium chelatase activity shows no oscillation, whereas the expression of CHLH (Xan-f) shows rhythmic variation. In contrast, the level of CHLI protein of soybean remains fairly constant in chloroplasts under similar conditions (12). Thus, magnesium chelatase activity must be primarily controlled by the expression of CHLI and CHLH, a somewhat long range regulatory system; additional post-transcriptional/translational regulation independent from rhythmic regulation is likely to also be involved in the control of the magnesium chelatase in vivo as a short range regulation system.…”

Section: Discussionmentioning

confidence: 95%

The CHLI1 Subunit of Arabidopsis thaliana Magnesium Chelatase Is a Target Protein of the Chloroplast Thioredoxin

Ikegami

Yoshimura

Motohashi

et al. 2007

Journal of Biological Chemistry

132

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Insertion of magnesium into protoporphyrin IX by magnesium chelatase is a key step in the chlorophyll biosynthetic pathway, which takes place in plant chloroplasts. ATP hydrolysis by the CHLI subunit of magnesium chelatase is an essential component of this reaction, and the activity of this enzyme is a primary determinant of the rate of magnesium insertion into the chlorophyll molecule (tetrapyrrole ring). Higher plant CHLI contains highly conserved cysteine residues and was recently identified as a candidate protein in a proteomic screen of thioredoxin target proteins (Balmer, Y., Koller, A., del Val, G., Manieri, W., Schurmann, P., and Buchanan, B. B. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 370 -375). To study the thioredoxin-dependent regulation of magnesium chelatase, we first investigated the effect of thioredoxin on the ATPase activity of CHLI1, a major isoform of CHLI in Arabidopsis thaliana. The ATPase activity of recombinant CHLI1 was found to be fully inactivated by oxidation and easily recovered by thioredoxin-assisted reduction, suggesting that CHLI1 is a target protein of thioredoxin. Moreover, we identified one crucial disulfide bond located in the C-terminal helical domain of CHLI1 protein, which may regulate the binding of the nucleotide to the N-terminal catalytic domain. The redox state of CHLI was also found to alter in a light-dependent manner in vivo. Moreover, we successfully observed stimulation of the magnesium chelatase activity in isolated chloroplasts by reduction. Our findings strongly suggest that chlorophyll biosynthesis is subject to chloroplast biogenesis regulation networks to coordinate them with the photosynthetic pathways in chloroplasts.The reactions encompassing higher plant chlorophyll biosynthesis consist of 12 enzymes that work in unison to produce chlorophyll a from 5-aminolevulinic acid and constitute one of the most important pathways for chloroplast biogenesis. Among the chlorophyll biosynthetic enzymes, magnesium chelatase (EC 6.6.1.1) catalyzes the insertion of Mg 2ϩ into protoporphyrin IX, the first dedicated step in chlorophyll biosynthesis. In (bacterio)chlorophyll a-producing prokaryotes (1), chlorophyll a-synthesizing bacteria, and higher plants, the magnesium chelatase complex consists of ϳ40-, ϳ70-, and ϳ140-kDa subunits named I, D, and H respectively (2, 3). The stoichiometry of these subunits within the magnesium chelatase complex as well as its complete three-dimensional structure is yet to be determined. From the biochemical analysis using recombinant subunits of magnesium chelatase from the photosynthetic bacteria Rhodobacter and cyanobacterium Synechocystis sp. PCC6803, it was determined that the largest H subunit binds protoporphyrin IX noncovalently (4), suggesting that the H subunit catalyzes the metal chelation reaction. Although ATP and Mg 2ϩ are required for the interaction between I and D subunits (5, 6), I-D complex formation is independent from the ATP hydrolysis activity of I subunit. In contrast, the ATP hydrolysis process is required for...

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Section: Discussionmentioning

confidence: 95%

The CHLI1 Subunit of Arabidopsis thaliana Magnesium Chelatase Is a Target Protein of the Chloroplast Thioredoxin

Ikegami

Yoshimura

Motohashi

et al. 2007

Journal of Biological Chemistry

132

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“…Such a signal might be monitored by the binding of these intermediates to enzymes such as the Mg-chelatase complex and especially to the ChlH and/or Gun4 proteins, which are able to bind both Proto and MgProto (32,33). The Mg-chelatase complex is postulated to change its location between the stroma and an association with the inner envelope of the plastid depending on the concentration of Mg 2ϩ inside the plastid (34). The turnover rate of MgProto on the Mg-chelatase complex might also regulate the localization of this complex and result in the transduction of a signal.…”

Section: Discussionmentioning

confidence: 99%

The steady-state level of Mg-protoporphyrin IX is not a determinant of plastid-to-nucleus signaling in Arabidopsis

Mochizuki

Tanaka

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

220

222

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“…However, the addition of phytyl PPi to chlorophyllide, a reaction catalyzed by chlorophyll synthase, is specifically associated with thylakoids. Nakayama et al (1998) demonstrated that Mg-chelatase activity, which catalyzes the insertion of Mg 2ϩ into protoporphyrin IX, was regulated by its subchloroplastic localization. The migration of Mg cheletase subunit ChlH from the stroma to envelope membranes, where it is functional, is regulated by the increase of Mg 2ϩ concentration into the stroma under illumination.…”

Section: The Biosynthesis Of Chlorophyllide and The Degradation Of Chmentioning

confidence: 99%

The Biochemical Machinery of Plastid Envelope Membranes

et al. 1998

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Plastids are semiautonomous organelles with a wide structural and functional diversity and unique biochemical pathways. As such, they are able to transcribe and translate the information present in their own genome but are strongly dependent on imported proteins that are encoded in the nuclear genome and translated in the cytoplasm. Plastids are present in every plant cell, with very few exceptions (such as the highly specialized male sexual cells), and their structural and functional diversity reflects their role in different cell types. According to their developmental stage, we distinguish them as juvenile (proplastids), differentiating, mature, and senescent. Meristematic cells contain proplastids, which ensure the continuity of plastids from generation to generation and are capable of considerable structural and metabolic plasticity to develop into various types of plastids that remain interconvertible. When leaves are grown in darkness, proplastids differentiate into etioplasts, which can be converted into chloroplasts under illumination.The metabolism of these various types of plastids is linked to the function of the tissue in which they are found. For instance, whereas the chief function of illuminated leaves is the assimilation of CO 2 by chloroplasts, root plastids are mainly involved in the assimilation of inorganic nitrogen. Amyloplasts, which contain large starch grains, behave as storage reservoirs in stems, roots, and tubers. Chromoplasts synthesize large amounts of carotenoids and are present in petals, fruits, and even roots. The interconversions between these different plastids are accompanied by dramatic changes, including the development or regression of internal membrane systems (e.g. thylakoids and prolamellar bodies) and the acquisition of specific enzymatic equipment reflecting specialized metabolism. However, at all stages of these transformations, the two limiting envelope membranes remain apparently unchanged.Located at the interface between plastids and the surrounding cytosol, the envelope is a key structure for the integration of plastid metabolism within the cell. Because plastids are semiautonomous organelles, a tight coordination between plastidial development and cell differentiation is required. Envelope membranes are an essential checkpoint between the expression of plastidial and nuclear genomes, for example, as the site for the specific recognition and transport of the precursor plastid proteins synthesized on cytosolic ribosomes. Plastid membranes contain an astonishing variety of specific lipids, including polar lipids (e.g. galactolipids, phospholipids, and SLs), pigments (e.g. carotenoids and chlorophylls), and prenylquinones (e.g. plastoquinone and tocopherols). This diversity requires complex metabolic pathways that are closely associated with envelope membranes.A unique biochemical machinery (Fig. 1) is present in envelope membranes and reflects the stage of development of the plastid and the specific metabolic requirements of the various tissues. PLASTID ENVELOPE ME...

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Cloning and Expression of the Soybean chlH Gene Encoding a Subunit of Mg-Chelatase and Localization of the Mg2+ Concentration-Dependent ChlH Protein within the Chloroplast

Cited by 83 publications

References 31 publications

The CHLI1 Subunit of Arabidopsis thaliana Magnesium Chelatase Is a Target Protein of the Chloroplast Thioredoxin

The CHLI1 Subunit of Arabidopsis thaliana Magnesium Chelatase Is a Target Protein of the Chloroplast Thioredoxin

The steady-state level of Mg-protoporphyrin IX is not a determinant of plastid-to-nucleus signaling in Arabidopsis

The Biochemical Machinery of Plastid Envelope Membranes

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