ArabidopsisChlorophyll 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 oxygeninduced 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-tonucleus retrograde signaling, that may monitor and maintain balance of chlorophyll precursor synthesis.

AtRsgA from Arabidopsis thaliana is important for maturation of the small subunit of the chloroplast ribosome

“…The metabolic signals that could cause the observed phenotypes in the atrsgA-i mutant include Mg-protoporphyrin IX (Mg-ProtoIX), beta-carotene and beta-cyclocitral (b-cyc). Mg-protoporphyrin IX is an intermediate in chlorophyll biosynthesis (Kim et al, 2013b). and might act by suppressing PhANG expression by binding to Long Hypocotyl 5 (HY) via Heat Shock 90 (HSP90) (Kindgren et al, 2011).…”

Identification of a Chlorophyll Dephytylase Involved in Chlorophyll Turnover in Arabidopsis

“…Chlorophyll is a pigment consisting of two moieties: a chlorin ring containing a magnesium ion at its center and a long hydrophobic phytol chain, joined by an ester bond. Once formed through highly coordinated pathways (Kim et al, 2013), chlorophylls are tightly bound to the photosystems until the partial or complete dismantling of the photosynthetic machinery in response to environmental and developmental cues, during which they undergo turnover or breakdown.…”

Assessing the Metabolic Impact of Nitrogen Availability Using a Compartmentalized Maize Leaf Genome-Scale Model

“…the N 2 WT, gln1-3 mutant, and gln1-4 mutant conditions), the flux compared with the N + WT reference condition decreases under maximum biomass through the chlorophyll cycle, chlorophyllide a biosynthesis, farnesyl diphosphate biosynthesis, methylerythritol phosphate pathway, and tetrapyrrole biosynthesis. Tetrapyrrole biosynthesis, chlorophyllide a biosynthesis, and the chlorophyll cycle link the production of chlorophyll from Glu (Tanaka and Tanaka, 2007;Kim et al, 2013). The methylerythritol phosphate pathway and farnesyl diphosphate biosynthesis lead to a reactant required for the production of chlorophyll a from chlorophyllide a (Lange and Ghassemian, 2003).…”