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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.

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Growth and pigmentation of the two chlM mutants. The wild- type strain as well as a yellow-in-the-dark mutant (y7) are shown for control. After inoculation the plates were incubated for 15 days either in the dark, or irradiated with the fluence rates indicated
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Fig3: Growth and pigmentation of the two chlM mutants. The wild- type strain as well as a yellow-in-the-dark mutant (y7) are shown for control. After inoculation the plates were incubated for 15 days either in the dark, or irradiated with the fluence rates indicated

Mentions: The two chlM mutants in the dark exhibited yellow pigmentation, very similar to that of the well studied y (yellow in the dark) mutants (Cahoon and Timko 2000).These y mutants have yellow colour in the dark, but are green in the light (Fig. 3). In contrast to the y mutants, the chlM mutants stayed yellow also upon exposure to low light. In addition, at medium light intensities (45 μmol m−2 s−1), growth of the chlM-2 mutant was inhibited (Fig. 3) and higher light intensities (500 μmol m−2 s−1) were required to inhibit growth of chlM-1. The increased light sensitivity of chlM-2 (Fig. 3) correlates with a greater severity of the mutation and about threefold higher levels of MgProto compared to chlM-1 (Table 1).Fig. 3


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)

Growth and pigmentation of the two chlM mutants. The wild- type strain as well as a yellow-in-the-dark mutant (y7) are shown for control. After inoculation the plates were incubated for 15 days either in the dark, or irradiated with the fluence rates indicated
© Copyright Policy
Related In: Results  -  Collection

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

Fig3: Growth and pigmentation of the two chlM mutants. The wild- type strain as well as a yellow-in-the-dark mutant (y7) are shown for control. After inoculation the plates were incubated for 15 days either in the dark, or irradiated with the fluence rates indicated
Mentions: The two chlM mutants in the dark exhibited yellow pigmentation, very similar to that of the well studied y (yellow in the dark) mutants (Cahoon and Timko 2000).These y mutants have yellow colour in the dark, but are green in the light (Fig. 3). In contrast to the y mutants, the chlM mutants stayed yellow also upon exposure to low light. In addition, at medium light intensities (45 μmol m−2 s−1), growth of the chlM-2 mutant was inhibited (Fig. 3) and higher light intensities (500 μmol m−2 s−1) were required to inhibit growth of chlM-1. The increased light sensitivity of chlM-2 (Fig. 3) correlates with a greater severity of the mutation and about threefold higher levels of MgProto compared to chlM-1 (Table 1).Fig. 3

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