title: Arabidopsis chlorophyll biosynthesis: an essential balance between the methylerythritol phosphate and tetrapyrrole pathways.
abstract: Chlorophyll, essential for photosynthesis, is composed of a chlorin ring and a geranylgeranyl diphosphate (GGPP)-derived isoprenoid, which are generated by the tetrapyrrole and methylerythritol phosphate (MEP) biosynthesis pathways, respectively. Although a functional MEP pathway is essential for plant viability, the underlying basis of the requirement has been unclear. We hypothesized that MEP pathway inhibition is lethal because a reduction in GGPP availability results in a stoichiometric imbalance in tetrapyrrolic chlorophyll precursors, which can cause deadly photooxidative stress. Consistent with this hypothesis, lethality of MEP pathway inhibition in Arabidopsis thaliana by fosmidomycin (FSM) is light dependent, and toxicity of MEP pathway inhibition is reduced by genetic and chemical impairment of the tetrapyrrole pathway. In addition, FSM treatment causes a transient accumulation of chlorophyllide and transcripts associated with singlet oxygen-induced stress. Furthermore, exogenous provision of the phytol molecule reduces FSM toxicity when the phytol can be modified for chlorophyll incorporation. These data provide an explanation for FSM toxicity and thereby provide enhanced understanding of the mechanisms of FSM resistance. This insight into MEP pathway inhibition consequences underlines the risk plants undertake to synthesize chlorophyll and suggests the existence of regulation, possibly involving chloroplast-to-nucleus retrograde signaling, that may monitor and maintain balance of chlorophyll precursor synthesis.
authors.affiliation: Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892.
authors.forename: Se
authors.initials: S
authors.lastname: Kim
authors.forename: Hagen
authors.initials: H
authors.lastname: Schlicke
authors.forename: Kalie
authors.initials: K
authors.lastname: Van Ree
authors.forename: Kristine
authors.initials: K
authors.lastname: Karvonen
authors.forename: Anant
authors.initials: A
authors.lastname: Subramaniam
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
authors.forename: Janet
authors.initials: J
authors.lastname: Braam
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics; D002338:Carotenoids / Q000096:biosynthesis; D002734:Chlorophyll / Q000096:biosynthesis*; D005578:Fosfomycin / Q000031:analogs & derivatives / Q000494:pharmacology; D020869:Gene Expression Profiling; D008027:Light; D053858:Metabolic Networks and Pathways / Q000235:genetics; D036226:Seedlings / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D013403:Sugar Phosphates / Q000096:biosynthesis; D045725:Tetrapyrroles / Q000096:biosynthesis
chemical_list: D029681:Arabidopsis Proteins; D013403:Sugar Phosphates; D045725:Tetrapyrroles; D002734:Chlorophyll; D005578:Fosfomycin; D002338:Carotenoids; C024640:fosmidomycin