Limits...
Chlorophyll-deficient mutants of Chlamydomonas reinhardtii that accumulate magnesium protoporphyrin IX.

Meinecke L, Alawady A, Schroda M, Willows R, Kobayashi MC, Niyogi KK, Grimm B, Beck CF - Plant Mol. Biol. (2010)

Bottom Line: The mutants, one with a missense mutation (chlM-1) and a second mutant with a splicing defect (chlM-2), do not accumulate chlorophyll, are yellow in the dark and dim light, and their growth is inhibited at higher light intensities.In the dark, both mutants showed a drastic reduction in the amounts of core proteins of photosystems I and II and light-harvesting chlorophyll a/b-binding proteins.No regulatory effects of the constitutively 7- to 18-fold increased MgProto levels on gene expression were detected, supporting previous results in which MgProto and heme in Chlamydomonas were assigned roles as second messengers only in the transient activation of genes by light.

View Article: PubMed Central - PubMed

Affiliation: Fakultaet fuer Biologie, Institut fuer Biologie III, Universitaet Freiburg, Schaenzlestrasse 1, 79104, Freiburg, Germany.

ABSTRACT
Two Chlamydomonas reinhardtii mutants defective in CHLM encoding Mg-protoporphyrin IX methyltransferase (MgPMT) were identified. The mutants, one with a missense mutation (chlM-1) and a second mutant with a splicing defect (chlM-2), do not accumulate chlorophyll, are yellow in the dark and dim light, and their growth is inhibited at higher light intensities. They accumulate Mg-protoporphyrin IX (MgProto), the substrate of MgPMT and this may be the cause for their light sensitivity. In the dark, both mutants showed a drastic reduction in the amounts of core proteins of photosystems I and II and light-harvesting chlorophyll a/b-binding proteins. However, LHC mRNAs accumulated above wild-type levels. The accumulation of the transcripts of the LHC and other genes that were expressed at higher levels in the mutants during dark incubation was attenuated in the initial phase of light exposure. No regulatory effects of the constitutively 7- to 18-fold increased MgProto levels on gene expression were detected, supporting previous results in which MgProto and heme in Chlamydomonas were assigned roles as second messengers only in the transient activation of genes by light.

Show MeSH

Related in: MedlinePlus

Scheme of the tetrapyrrole biosynthetic pathway in Chlamydomonas reinhardtii and vascular plants. Shown are the major intermediates and the genes mentioned in the text. Dashed lines indicate multiple steps
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2837180&req=5

Fig1: Scheme of the tetrapyrrole biosynthetic pathway in Chlamydomonas reinhardtii and vascular plants. Shown are the major intermediates and the genes mentioned in the text. Dashed lines indicate multiple steps

Mentions: The eukaryotic chlorophyll biosynthetic pathway leads to chlorophylls a and b (Fig. 1). Each enzymatic intermediate is well-defined, and enzymatic activities and genes have been detected and described for many steps of the pathway (Beale 1999; Moulin and Smith 2005). Although generally quite similar, the pathways for tetrapyrrole biosynthesis in vascular plants and C. reinhardtii show some distinct differences. For example, heme in the green alga appears to be synthesized exclusively in plastids. Only single genes encoding protoporphyrinogen (Protogen) oxidase and ferrochelatase were found in the C. reinhardtii genome and the corresponding gene products were localized to the chloroplast, suggesting that C. reinhardtii possesses only one single heme-synthesizing pathway located in this organelle (van Lis et al. 2005). Tobacco and cucumber were shown to have two genes for each of these enzymatic steps (Fig. 1) allowing the parallel synthesis of heme in plastids and mitochondria (Lermontova et al. 1997; Suzuki et al. 2002). Also, unlike angiosperms but similar to gymnosperms, C. reinhardtii cells have both a light-independent protochlorophyllide oxidoreductase (POR) consisting of three proteins (ChlN, ChlB, ChlL) encoded by the chloroplast genome, and a light-dependent POR (Fig. 1). C. reinhardtii mutants defective in the light-independent conversion of protochlorophyllide to chlorophyllide are yellow in the dark but, due to the presence of a light-dependent POR, are green in the light. Defects in at least 7 nuclear loci have been shown to cause a yellow-in-the-dark mutant phenotype (designated y-1 and y-5 to y-10). These loci are required for the production of a functional light-independent POR enzyme (Cahoon and Timko 2000).Fig. 1


Chlorophyll-deficient mutants of Chlamydomonas reinhardtii that accumulate magnesium protoporphyrin IX.

Meinecke L, Alawady A, Schroda M, Willows R, Kobayashi MC, Niyogi KK, Grimm B, Beck CF - Plant Mol. Biol. (2010)

Scheme of the tetrapyrrole biosynthetic pathway in Chlamydomonas reinhardtii and vascular plants. Shown are the major intermediates and the genes mentioned in the text. Dashed lines indicate multiple steps
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2837180&req=5

Fig1: Scheme of the tetrapyrrole biosynthetic pathway in Chlamydomonas reinhardtii and vascular plants. Shown are the major intermediates and the genes mentioned in the text. Dashed lines indicate multiple steps
Mentions: The eukaryotic chlorophyll biosynthetic pathway leads to chlorophylls a and b (Fig. 1). Each enzymatic intermediate is well-defined, and enzymatic activities and genes have been detected and described for many steps of the pathway (Beale 1999; Moulin and Smith 2005). Although generally quite similar, the pathways for tetrapyrrole biosynthesis in vascular plants and C. reinhardtii show some distinct differences. For example, heme in the green alga appears to be synthesized exclusively in plastids. Only single genes encoding protoporphyrinogen (Protogen) oxidase and ferrochelatase were found in the C. reinhardtii genome and the corresponding gene products were localized to the chloroplast, suggesting that C. reinhardtii possesses only one single heme-synthesizing pathway located in this organelle (van Lis et al. 2005). Tobacco and cucumber were shown to have two genes for each of these enzymatic steps (Fig. 1) allowing the parallel synthesis of heme in plastids and mitochondria (Lermontova et al. 1997; Suzuki et al. 2002). Also, unlike angiosperms but similar to gymnosperms, C. reinhardtii cells have both a light-independent protochlorophyllide oxidoreductase (POR) consisting of three proteins (ChlN, ChlB, ChlL) encoded by the chloroplast genome, and a light-dependent POR (Fig. 1). C. reinhardtii mutants defective in the light-independent conversion of protochlorophyllide to chlorophyllide are yellow in the dark but, due to the presence of a light-dependent POR, are green in the light. Defects in at least 7 nuclear loci have been shown to cause a yellow-in-the-dark mutant phenotype (designated y-1 and y-5 to y-10). These loci are required for the production of a functional light-independent POR enzyme (Cahoon and Timko 2000).Fig. 1

Bottom Line: The mutants, one with a missense mutation (chlM-1) and a second mutant with a splicing defect (chlM-2), do not accumulate chlorophyll, are yellow in the dark and dim light, and their growth is inhibited at higher light intensities.In the dark, both mutants showed a drastic reduction in the amounts of core proteins of photosystems I and II and light-harvesting chlorophyll a/b-binding proteins.No regulatory effects of the constitutively 7- to 18-fold increased MgProto levels on gene expression were detected, supporting previous results in which MgProto and heme in Chlamydomonas were assigned roles as second messengers only in the transient activation of genes by light.

View Article: PubMed Central - PubMed

Affiliation: Fakultaet fuer Biologie, Institut fuer Biologie III, Universitaet Freiburg, Schaenzlestrasse 1, 79104, Freiburg, Germany.

ABSTRACT
Two Chlamydomonas reinhardtii mutants defective in CHLM encoding Mg-protoporphyrin IX methyltransferase (MgPMT) were identified. The mutants, one with a missense mutation (chlM-1) and a second mutant with a splicing defect (chlM-2), do not accumulate chlorophyll, are yellow in the dark and dim light, and their growth is inhibited at higher light intensities. They accumulate Mg-protoporphyrin IX (MgProto), the substrate of MgPMT and this may be the cause for their light sensitivity. In the dark, both mutants showed a drastic reduction in the amounts of core proteins of photosystems I and II and light-harvesting chlorophyll a/b-binding proteins. However, LHC mRNAs accumulated above wild-type levels. The accumulation of the transcripts of the LHC and other genes that were expressed at higher levels in the mutants during dark incubation was attenuated in the initial phase of light exposure. No regulatory effects of the constitutively 7- to 18-fold increased MgProto levels on gene expression were detected, supporting previous results in which MgProto and heme in Chlamydomonas were assigned roles as second messengers only in the transient activation of genes by light.

Show MeSH
Related in: MedlinePlus