Green or red: what stops the traffic in the tetrapyrrole pathway?
Regulation of tetrapyrrole biosynthesis is crucial to plant metabolism. The two pivotal control points are formation of the initial precursor, 5-aminolaevulinic acid (ALA), and the metal-ion insertion step: chelation of Fe(2+) into protoporphyrin IX leads to haem and phytochromobilin, whereas insertion of Mg(2+) is the first step to chlorophyll. Recent studies with mutants and transgenic plants have demonstrated that perturbation of the branch point affects ALA formation. Moreover, one of the signals that controls the expression of genes for nuclear-encoded chloroplast proteins has been shown to be Mg-protoporphyrin-IX. Here, we discuss the regulation of branch-point flux and the relative contributions of the haem and chlorophyll branches to the regulation of ALA synthesis and thus to flow through the tetrapyrrole pathway.
Cornah
Johanna E
JE
Institute of Cell and Molecular Biology, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, Scotland, UK EH9 3JR.
Terry
Matthew J
MJ
Smith
Alison G
AG
D002734:Chlorophyll / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D008670:Metals / Q000378:metabolism; D010944:Plants / Q000235:genetics / Q000378:metabolism*; D011758:Pyrroles / Q000378:metabolism*; D045725:Tetrapyrroles
D008670:Metals; D011758:Pyrroles; D045725:Tetrapyrroles; D002734:Chlorophyll; D006418:Heme