Stimulation of Appearance of Extraplastidic Tetrapyrroles by a Photooxidative Treatment of the Plastids*

Thomsen, B.; Oelze‐Karow, H.; Schuster, C.; Mohr, Hans

doi:10.1111/j.1751-1097.1993.tb04957.x

Cited by 9 publications

(3 citation statements)

References 48 publications

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“…Treatment of seedlings with the phytoene desaturase‐inhibitor herbicide, Norflurazon, under WL leads to photobleaching of the chloroplasts and the loss of light‐induced expression of photosynthesis‐related genes. Since phytochrome synthesis is unaffected under these conditions (Thomsen et al ., 1993), this has been interpreted as resulting from the absence of a plastid signal required for normal gene expression. As seen for native transcription, light‐responsive accumulation of GUS activity from the HEMA1 promoter was severely inhibited by Norflurazon application (Figure 8).…”

Section: Resultsmentioning

confidence: 99%

Regulation of HEMA1 expression by phytochrome and a plastid signal during de‐etiolation in Arabidopsis thaliana

McCormac¹,

Fischer²,

Kumar³

et al. 2001

The Plant Journal

128

134

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SummaryThe synthesis of 5-aminolevulinic acid (ALA) is the rate-limiting step for the formation of all plant tetrapyrroles, including chlorophyll and heme, and regulation of ALA synthesis is therefore critical to plant development. Glutamyl-tRNA reductase (GluTR) is the ®rst committed enzyme of this pathway and is encoded by a small family of nuclear HEMA genes. Here, we have used transgenic Arabidopsis (Arabidopsis thaliana L. Col) lines expressing chimeric HEMA1 promoter:gusA fusion genes, combined with RNA gel blot analyses, to characterise the light-mediated regulation of the Arabidopsis HEMA1 gene during de-etiolation. HEMA1 was expressed strongly, but not exclusively, in photosynthetic tissues and was shown to be light regulated at the transcriptional level by the phytochrome family of photoreceptors acting in both the far-red high irradiance and low¯uence response modes. The HEMA2 gene, which is expressed only in roots of seedlings, was not light regulated. Analysis of truncated HEMA1 promoter constructs demonstrated that a ±199/+252 promoter fragment was suf®cient to confer full light-responsiveness to gusA expression. This fragment contained GT-1/I-box and CCA-1 binding sites that are implicated as the light-responsive cis elements. Both the full-length and truncated HEMA1 promoters required the presence of intact chloroplasts for full expression, consistent with previous indications that light and plastid factor signals converge to co-ordinately regulate expression of photosynthesis-related nuclear genes. These results provide the most comprehensive analysis to date of the light-regulation of a tetrapyrrole biosynthetic gene and support a direct link between regulation of HEMA1 transcription and chlorophyll accumulation during seedling de-etiolation.

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Section: Resultsmentioning

confidence: 99%

Regulation of HEMA1 expression by phytochrome and a plastid signal during de‐etiolation in Arabidopsis thaliana

McCormac¹,

Fischer²,

Kumar³

et al. 2001

The Plant Journal

128

134

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“…Other lines of evidence, e.g. photodestruction of chloroplasts (Thomsen et al, 1993), mutations affecting the tRNA Glu (Hess et al, 1992), and inhibition of GSA-AT activity by gabaculin (Flint, 1984), also support the C 4 pathway of ALA biosynthesis in plants. We describe studies of antisense HEMA1 Arabidopsis plants that unequivocally demonstrate the involvement of GluTR in ALA formation.…”

mentioning

confidence: 99%

Antisense HEMA1 RNA Expression Inhibits Heme and Chlorophyll Biosynthesis in Arabidopsis

2000

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5-Aminolevulinic acid (ALA) is a precursor in the biosynthesis of tetrapyrroles including chlorophylls and heme. The formation of ALA involves two enzymatic steps which take place in the chloroplast in plants. The first enzyme, glutamyl-tRNA reductase, and the second enzyme, glutamate-1-semialdehyde-2,1-aminomutase, are encoded by the nuclear HEMA and GSA genes, respectively. To assess the significance of the HEMA gene for chlorophyll and heme synthesis, transgenic Arabidopsis plants that expressed antisense HEMA1 mRNA from the constitutive cauliflower mosaic virus 35S promoter were generated. These plants exhibited varying degrees of chlorophyll deficiency, ranging from patchy yellow to total yellow. Analysis indicated that these plants had decreased levels of chlorophyll, non-covalently bound hemes, and ALA; their levels were proportional to the level of glutamyl-tRNA reductase expression and were inversely related to the levels of antisense HEMA transcripts. Plants that lacked chlorophyll failed to survive under normal growth conditions, indicating that HEMA gene expression is essential for growth.

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“…Etiolated seedlings grown on MS media were harvested at 11 days for holophytochrome quantification. More accurate measurements were obtained by the supplementation of media with 5 μ m Norflurazon, a treatment known not to adversely affect phytochrome levels (Thomsen et al. , 1993).…”

Section: Methodsmentioning

confidence: 99%

Misregulation of tetrapyrrole biosynthesis in transgenic tobacco seedlings expressing mammalian biliverdin reductase

et al. 2003

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SummaryPrevious studies have established that the expression of mammalian biliverdin IXa reductase (BVR) in transgenic tobacco (Nicotiana tabacum cv. Maryland Mammoth) resulted in the loss of photoregulatory activity of all phytochromes together with a pronounced chlorophyll de®ciency. This study was undertaken to assess the contribution of BVR-mediated alteration of tetrapyrrole metabolism to the observed phenotypes of BVR transgenic plants. BVR expression in dark-grown plants led to the reduced accumulation of protochlorophyllide and transcripts for the two committed enzymes for 5-aminolevulinic acid (ALA) synthesis despite the marked increased capacity for synthesis of ALA. Together with the observation that Mgporphyrin accumulation in dark-grown seedlings treated with an iron chelator was unaffected by BVR expression, these results indicate that BVR diverts tetrapyrrole metabolism toward heme synthesis while also reducing heme levels to de-repress ALA synthesis. By contrast with dark-grown seedlings, light-grown BVR plants showed a marked inhibition of ALA synthesis compared with wild-type plants ± a result that was correlated with the disappearance of the CHL I subunit of Mg-chelatase and an increase in heme oxygenase protein levels. As transcript levels of all tetrapyrrole biosynthetic genes tested were not strongly affected by BVR expression, these results implicate misregulated tetrapyrrole metabolism to be a major mechanism for BVR-dependent inhibition of chlorophyll biosynthesis in light-grown plants.

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Stimulation of Appearance of Extraplastidic Tetrapyrroles by a Photooxidative Treatment of the Plastids*

Cited by 9 publications

References 48 publications

Regulation of HEMA1 expression by phytochrome and a plastid signal during de‐etiolation in Arabidopsis thaliana

Regulation of HEMA1 expression by phytochrome and a plastid signal during de‐etiolation in Arabidopsis thaliana

Antisense HEMA1 RNA Expression Inhibits Heme and Chlorophyll Biosynthesis in Arabidopsis

Misregulation of tetrapyrrole biosynthesis in transgenic tobacco seedlings expressing mammalian biliverdin reductase

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