Sustaining S‐adenosyl‐l‐methionine‐dependent methyltransferase activity in plant cells

Abstract

Many biochemical reactions in plants involve the transfer of a methyl group from S‐adenosyl‐l‐methionine (SAM). The transfer of the methyl group from SAM generates S‐adenosyl‐l‐homocysteine (SAH), a potent inhibitor of SAM‐dependent methyltransferases (MTs). To mitigate the toxic effects of SAH on MT activity, SAH is removed by SAH hydrolase (SAHH, EC 3.3.1.1) in a reaction generating homocysteine and adenosine (Ado). However, SAHH catalyzes a reversible reaction that is favored to move in the direction of SAH hydrolysis only by removal of these products. Removal of Ado is reported to exert a greater influence on promoting SAH hydrolysis. Whereas animals appear to rely upon Ado deaminase (EC 3.5.4.4) to catabolize Ado, plants appear to use adenosine kinase (EC 2.7.1.20) for this important role. Compounds undergoing methylation represent a broad spectrum of chemically diverse substrates ranging from nucleic acids, lipids and cell wall components to comparatively simpler amines, alcohols and metal halides. Given the diverse nature of methyl acceptor compounds, it is very likely that the demand for SAM synthesis and SAH removal changes both temporally and spatially during the course of plant growth and development. Plants also use SAM as a precursor for the synthesis of ethylene, polyamines, biotin and nicotianamine. These uses are also expected to undergo changes reflective of the metabolic activities of different plants, plant organs, or cells. This review examines the various uses of SAM in plants and addresses how they allocate this resource to satisfy potentially competing needs.

Identification of Phosphomethylethanolamine N-Methyltransferase from Arabidopsis and Its Role in Choline and Phospholipid Metabolism

“…This temporal regulation should reduce or prevent the production of PMEA in the dark when the continued synthesis of PCho is energetically disadvantageous to the plant. Unregulated operation of this pathway in the dark poses a potentially significant depletion and/or redirection of energy because each molecule of PCho produced requires seven molecules of ATP for EA phosphorylation, AdoMet production, and AdoHcy recycling (48). The reduced production of PMEA by PEAMT in the dark should eventually lead to the depletion of PMEA.…”

ArabidopsisSAMT1 Defines a Plastid Transporter Regulating Plastid Biogenesis and Plant Development

“…ethz.ch/]). Interestingly, senescence is considered as a period of SAM limitation (Moffatt and Weretilnyk, 2001). In this context, the accumulation of g-tocopherol in TTO-Nb SAMT1-silenced plants ( Figure 8B) and in senescing tobacco leaves (Falk et al, 2003) could reflect a decreased plastid SAM import.…”

“…Additionally, SAM is a source of aminoalkyl and amino groups used for the biogenesis of polyamines and biotin (Hanson and Roje, 2001;Moffatt and Weretilnyk, 2001;Fontecave et al, 2004). In plants, SAM is also converted to 1-aminocyclopropane-1-carboxylic acid, the direct precursor of the plant hormone ethylene (Kevin et al, 2002).…”

Proteins involved in biotic and abiotic stress responses as the most significant biomarkers in the ripening of Pinot Noir skins

“…In addition to its activity as the precursor in the biosynthesis of the polyamines spermidine and spermine and of the plant hormone ethylene, SAM is the principal methyl donor of the cell being the substrate of many specific methyltransferases that act on a wide range of molecules, moving from nucleic acid to secondary metabolites (Moffatt and Weretilnyk 2001). Spot 2215, which sharply declined its expression in mature skins resulting in a very negative coefficient for RS38 was identified as SAMS.…”