Analysis of gun phenotype in barley magnesium chelatase and Mg-protoporphyrin IX monomethyl ester cyclase mutants

Gadjieva, Rena; Axelsson, Eva; Olsson, Ulf; Hansson, Mats

doi:10.1016/j.plaphy.2005.08.003

Cited by 50 publications

(51 citation statements)

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“…Magnesium protoporphyrin methyl ester itself may be a positive effector. In support of this latter hypothesis (24), have shown that, in the absence of Norflurazon, the barley xantha l mutant that is defective in the magnesium protoporphyrin methyl ester cyclase, accumulates magnesium protoporphyrin IX methyl ester and has a high level of LHCB expression. In addition, Alawady and Grimm (8) reported positive correlation between LHCB expression and methyltransferase activity in tobacco CHLM antisense and sense RNA mutants.…”

Section: Discussionmentioning

confidence: 82%

“…Moreover, because of the possibility of substrate channeling occurring between magnesium chelatase and magnesium protoporphyrin IX methyltransferase, it was not possible to clearly distinguish the specific contributions of magnesium protoporphyrin IX and its methyl ester. Supporting the intricacy of the regulation, it has recently been shown that the barley xantha-l mutant, defective in the magnesium protoporphyrin IX methyl ester cyclization step, has a non-gun phenotype in the presence of Norflurazon (23,24). In the absence of Norflurazon, the mutant has a high level of LHCB gene expression despite the accumulation of magnesium protoporphyrin IX methyl ester.…”

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confidence: 99%

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Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Pontier

Albrieux

Joyard

et al. 2007

Journal of Biological Chemistry

124

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Protoporphyrin IX is the last common intermediate between the heme and chlorophyll biosynthesis pathways. The addition of magnesium directs this molecule toward chlorophyll biosynthesis. The first step downstream from the branchpoint is catalyzed by the magnesium chelatase and is a highly regulated process. The corresponding product, magnesium protoporphyrin IX, has been proposed to play an important role as a signaling molecule implicated in plastid-to-nucleus communication. To get more information on the chlorophyll biosynthesis pathway and on magnesium protoporphyrin IX derivative functions, we have identified an magnesium protoporphyrin IX methyltransferase (CHLM) knock-out mutant in Arabidopsis in which the mutation induces a blockage downstream from magnesium protoporphyrin IX and an accumulation of this chlorophyll biosynthesis intermediate. Our results demonstrate that the CHLM gene is essential for the formation of chlorophyll and subsequently for the formation of photosystems I and II and cytochrome b6f complexes. Analysis of gene expression in the chlm mutant provides an independent indication that magnesium protoporphyrin IX is a negative effector of nuclear photosynthetic gene expression, as previously reported. Moreover, it suggests the possible implication of magnesium protoporphyrin IX methyl ester, the product of CHLM, in chloroplast-to-nucleus signaling. Finally, post-transcriptional up-regulation of the level of the CHLH subunit of the magnesium chelatase has been detected in the chlm mutant and most likely corresponds to specific accumulation of this protein inside plastids. This result suggests that the CHLH subunit might play an important regulatory role when the chlorophyll biosynthetic pathway is disrupted at this particular step.Chloroplast development depends on the coordinated synthesis of chlorophylls and cognate proteins and on their specific integration into photosynthetic complexes (for review, see Ref. 1). Chlorophylls are magnesium tetrapyrrole molecules resulting from condensation of ALA.2 Insertion of magnesium into protoporphyrin IX, the last common intermediate of hemes and chlorophylls, is catalyzed by magnesium chelatase, a membrane-interacting multisubunit enzyme containing 3 different soluble proteins: CHLH, CHLI, and CHLD (2-5). In the next step, magnesium protoporphyrin IX is methylated by a membrane Ado-Met-dependent methyltransferase. In Arabidopsis the gene At4g25080 or CHLM has been identified as encoding the methyltransferase enzyme, and the product of this single gene has been reported to be present in the two chloroplast membrane systems; that is, the envelope and the thylakoids (6). Whereas a sequence homologous to CHLM has been identified in tobacco (7), the existence in plants of an additional and quite dissimilar gene for magnesium protoporphyrin IX methylation has not been totally excluded. Expression analysis of tobacco CHLM revealed posttranslational activation of methyltransferase activity during greening and direct interaction of CHLM with the CHLH subun...

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Section: Discussionmentioning

confidence: 82%

mentioning

confidence: 99%

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Pontier

Albrieux

Joyard

et al. 2007

Journal of Biological Chemistry

124

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“…Mutants unable to synthesize Mg-protoporphyrin contain only unfenestrated thylakoids and lack prolamellar bodies (von Wettstein et al, 1995). Interestingly, Mg-protoporphyrin suppresses nuclear expression of Lhab1 and other genes encoding chloroplast-localized proteins (Kropat et al, 2000;Strand et al, 2003;Alawady and Grimm, 2005;Gadjieva et al, 2005), which suggests that Mg-protoporphyrin plays the essential role of signal molecule in the regulation of these processes. In addition, Mg-protoporphyrin and heme are known to regulate the first biosynthetic steps of their common pathway (Vasileuskaya et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Recessiveness and Dominance in Barley Mutants Deficient in Mg-Chelatase Subunit D, an AAA Protein Involved in Chlorophyll Biosynthesis

et al. 2006

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Mg-chelatase catalyzes the insertion of Mg 2þ into protoporphyrin IX at the first committed step of the chlorophyll biosynthetic pathway. It consists of three subunits: I, D, and H. The I subunit belongs to the AAA protein superfamily (ATPases associated with various cellular activities) that is known to form hexameric ring structures in an ATP-dependant fashion. Dominant mutations in the I subunit revealed that it functions in a cooperative manner. We demonstrated that the D subunit forms ATP-independent oligomeric structures and should also be classified as an AAA protein. Furthermore, we addressed the question of cooperativity of the D subunit with barley (Hordeum vulgare) mutant analyses. The recessive behavior in vivo was explained by the absence of mutant proteins in the barley cell. Analogous mutations in Rhodobacter capsulatus and the resulting D proteins were studied in vitro. Mixtures of wild-type and mutant R. capsulatus D subunits showed a lower activity compared with wild-type subunits alone. Thus, the mutant D subunits displayed dominant behavior in vitro, revealing cooperativity between the D subunits in the oligomeric state. We propose a model where the D oligomer forms a platform for the stepwise assembly of the I subunits. The cooperative behavior suggests that the D oligomer takes an active part in the conformational dynamics between the subunits of the enzyme.

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“…The product of Mg-chelatase, Mg-protoporphyrin IX, has been suggested to function directly as a retrograde plastid/nuclear signaling molecule in both Arabidopsis (Strand et al, 2003) and barley (Gadjieva et al, 2005). Accumulation of Mg-protoporphyrinogen IX was suggested to cause transcriptional repression of nuclear-encoded chloroplast genes (Strand et al, 2003;Pontier et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

Suppression of the Barleyuroporphyrinogen III synthaseGene by aDsActivation Tagging Element Generates Developmental Photosensitivity

et al. 2009

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Chlorophyll production involves the synthesis of photoreactive intermediates that, when in excess, are toxic due to the production of reactive oxygen species (ROS). A novel, activation-tagged barley (Hordeum vulgare) mutant is described that results from antisense suppression of a uroporphyrinogen III synthase (Uros) gene, the product of which catalyzes the sixth step in the synthesis of chlorophyll and heme. In homozygous mutant plants, uroporphyrin(ogen) I accumulates by spontaneous cyclization of hydroxyl methylbilane, the substrate of Uros. Accumulation of this tetrapyrrole intermediate results in photosensitive cell death due to the production of ROS. The efficiency of Uros gene suppression is developmentally regulated, being most effective in mature seedling leaves compared with newly emergent leaves. Reduced transcript accumulation of a number of nuclear-encoded photosynthesis genes occurs in the mutant, even under 3% light conditions, consistent with a retrograde plastid-nuclear signaling mechanism arising from Uros gene suppression. A similar set of nuclear genes was repressed in wild-type barley following treatment with a singlet oxygen-generating herbicide, but not by a superoxide generating herbicide, suggesting that the retrograde signaling apparent in the mutant is specific to singlet oxygen.

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Analysis of gun phenotype in barley magnesium chelatase and Mg-protoporphyrin IX monomethyl ester cyclase mutants

Cited by 50 publications

References 28 publications

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Knock-out of the Magnesium Protoporphyrin IX Methyltransferase Gene in Arabidopsis

Recessiveness and Dominance in Barley Mutants Deficient in Mg-Chelatase Subunit D, an AAA Protein Involved in Chlorophyll Biosynthesis

Suppression of the Barleyuroporphyrinogen III synthaseGene by aDsActivation Tagging Element Generates Developmental Photosensitivity

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