Abstract
Magnesium-protoporphyrin IX chelatase (Mg-chelatase) is located at the branchpoint of tetrapyrrole biosynthesis, at which point protoporphyrin IX is distributed for the synthesis of chlorophyll and heme. We investigated the regulatory contribution of Mg-chelatase to the flow of metabolites. In plants, the enzyme complex consists of three subunits, designated CHL D, CHL I, and CHL H. Transgenic tobacco (Nicotiana tabacum) plants expressing antisense RNA for the Mg-chelatase subunit CHL H were analyzed to elucidate further the role of Mg-chelatase in the distribution of protoporphyrin IX into the branched tetrapyrrolic pathway. The transgenic plants displayed a reduced growth rate and chlorophyll deficiency. Both phenotypical properties were correlated with lower Mg-chelatase activity. Unexpectedly, less protoporphyrin IX and heme accumulated, and a decrease in 5-aminolevulinate (ALA)-synthesizing capacity and ALA dehydratase activity paralleled the progressive reduction in Mg-chelatase activity in the transformants compared with control plants. The reduced activities of the early enzymatic steps corresponded with lower levels of transcripts encoding glutamyl-tRNA reductase and ALA-dehydratase. The decreased expression and activities of early enzymes in the pathway could be explained by a feedback-controlled mechanism in response to lower Mg-chelatase activity. We discuss intercompartmental signaling that synchronizes the activities of the first steps in tetrapyrrolic metabolism with the late steps for the synthesis of end products.
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Claims 9
Claim · model-written summary
Antisense tobacco plants had reduced growth rate.
- Taxon
- tobacco (Nicotiana tabacum)
Nicotiana tabacume0 - Treatment
- expressing antisense RNA for the Mg-chelatase subunit CHL He0
- Gene
- Mg-chelatase subunit CHL He0
- Outcome
- growth ratee1
- Direction
- reducede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Transgenic tobacco (Nicotiana tabacum) plants expressing antisense RNA for the Mg-chelatase subunit CHL H”
e1“The transgenic plants displayed a reduced growth rate and chlorophyll deficiency”
Claim · model-written summary
Antisense tobacco plants were chlorophyll deficient.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Treatment
- expressing antisense RNA for the Mg-chelatase subunit CHL He0
- Gene
- Mg-chelatase subunit CHL He0
- Outcome
- chlorophyll deficiencye1
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Transgenic tobacco (Nicotiana tabacum) plants expressing antisense RNA for the Mg-chelatase subunit CHL H”
e1“The transgenic plants displayed a reduced growth rate and chlorophyll deficiency”
Claim · model-written summary
Reduced growth and chlorophyll deficiency correlated with lower Mg-chelatase activity.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Gene
- Mg-chelatasee1
- Outcome
- phenotypical propertiese1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“Both phenotypical properties were correlated with lower Mg-chelatase activity”
Claim · model-written summary
Transformants accumulated less protoporphyrin IX and heme than controls.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Treatment
- transformantse2
- Outcome
- protoporphyrin IX and hemee1
- Direction
- lesse1
- Comparator
- control plantse2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“less protoporphyrin IX and heme accumulated”
e2“transformants compared with control plants”
Claim · model-written summary
ALA-synthesizing capacity decreased as Mg-chelatase activity declined.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Gene
- Mg-chelatasee1
- Outcome
- 5-aminolevulinate (ALA)-synthesizing capacitye1
- Direction
- decreasee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“a decrease in 5-aminolevulinate (ALA)-synthesizing capacity and ALA dehydratase activity paralleled the progressive reduction in Mg-chelatase activity”
Claim · model-written summary
ALA dehydratase activity decreased as Mg-chelatase activity declined.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Gene
- Mg-chelatasee1
- Outcome
- ALA dehydratase activitye1
- Direction
- decreasee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“a decrease in 5-aminolevulinate (ALA)-synthesizing capacity and ALA dehydratase activity paralleled the progressive reduction in Mg-chelatase activity”
Claim · model-written summary
Transcripts encoding glutamyl-tRNA reductase were lower with reduced early pathway activity.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Gene
- glutamyl-tRNA reductasee1
- Outcome
- transcripts encoding glutamyl-tRNA reductasee1
- Direction
- lowere1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“The reduced activities of the early enzymatic steps corresponded with lower levels of transcripts encoding glutamyl-tRNA reductase and ALA-dehydratase”
Claim · model-written summary
Transcripts encoding ALA-dehydratase were lower with reduced early pathway activity.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Gene
- ALA-dehydratasee1
- Outcome
- ALA-dehydratasee1
- Direction
- lowere1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“The reduced activities of the early enzymatic steps corresponded with lower levels of transcripts encoding glutamyl-tRNA reductase and ALA-dehydratase”
Claim · model-written summary
Authors propose feedback control in response to reduced Mg-chelatase activity as an explanation for lower early enzyme expression and activity.
- Taxon
- tobacco (Nicotiana tabacum)Nicotiana tabacume0
- Gene
- Mg-chelatasee1
- Outcome
- decreased expression and activities of early enzymese1
- Qualifier
- feedback-controlled mechanisme1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tobacco (Nicotiana tabacum)”
e1“The decreased expression and activities of early enzymes in the pathway could be explained by a feedback-controlled mechanism in response to lower Mg-chelatase activity”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.