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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
Regulation of HEMA1 expression by phytochrome and a plastid signal during de-etiolation in Arabidopsis thaliana
The 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 first 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 HEMA1gene 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 fluence 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 sufficient 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 HEMA1promoters 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.
chloroplast development, chlorophyll synthesis, glutamyl-tRNA reductase, aminolevulinicacid, light regulation.
0960-7412
549-561
McCormac, A.C.
6815d048-4a55-43f0-b59f-8c4613477504
Fischer, A.
798c82d9-aa26-4b05-8604-b80f4db8d75e
Kumar, A.M.
99c00335-a709-4db8-af47-92c3146ab2ed
Soll, D.
a8f7f8da-2562-4cdd-b4cd-15d46b846ea1
Terry, M.J.
a8c2cd6b-8d35-4053-8d77-3841c2427c3b
McCormac, A.C.
6815d048-4a55-43f0-b59f-8c4613477504
Fischer, A.
798c82d9-aa26-4b05-8604-b80f4db8d75e
Kumar, A.M.
99c00335-a709-4db8-af47-92c3146ab2ed
Soll, D.
a8f7f8da-2562-4cdd-b4cd-15d46b846ea1
Terry, M.J.
a8c2cd6b-8d35-4053-8d77-3841c2427c3b

McCormac, A.C., Fischer, A., Kumar, A.M., Soll, D. and Terry, M.J. (2001) Regulation of HEMA1 expression by phytochrome and a plastid signal during de-etiolation in Arabidopsis thaliana. The Plant Journal, 25 (5), 549-561. (doi:10.1046/j.1365-313x.2001.00986.x).

Record type: Article

Abstract

The 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 first 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 HEMA1gene 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 fluence 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 sufficient 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 HEMA1promoters 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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Published date: March 2001
Keywords: chloroplast development, chlorophyll synthesis, glutamyl-tRNA reductase, aminolevulinicacid, light regulation.

Identifiers

Local EPrints ID: 37640
URI: http://eprints.soton.ac.uk/id/eprint/37640
ISSN: 0960-7412
PURE UUID: 01e77d7c-7f4f-4d0a-97e5-3b7e6a107027
ORCID for M.J. Terry: ORCID iD orcid.org/0000-0001-5002-2708

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Date deposited: 25 May 2006
Last modified: 16 Mar 2024 02:52

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Contributors

Author: A.C. McCormac
Author: A. Fischer
Author: A.M. Kumar
Author: D. Soll
Author: M.J. Terry ORCID iD

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