PlantSterolMetabolism
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Biogenesis, molecular regulation and function of plant isoprenoids

Isoprenoids represent the oldest class of known low molecular-mass natural products synthesized by plants. Their biogenesis in plastids, mitochondria and the endoplasmic reticulum–cytosol proceed invariably from the C5 building blocks, isopentenyl diphosphate and/or dimethylallyl diphosphate according to complex and reiterated mechanisms. Compounds derived from the pathway exhibit a diverse spectrum of biological functions. This review centers on advances obtained in the field based on combined use of biochemical, molecular biology and genetic approaches. The function and evolutionary implications of this metabolism are discussed in relation with seminal informations gathered from distantly but related organisms.

  
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Biochemistry and Molecular Biology of the Isoprenoid Biosynthetic Pathway in Plants - Annual Review of Plant Physiology and Plant Molecular Biology, 46(1):521

Biochemistry and Molecular Biology of the Isoprenoid Biosynthetic Pathway in Plants - Annual Review of Plant Physiology and Plant Molecular Biology, 46(1):521 | PlantSterolMetabolism | Scoop.it

This review first summarizes the diverse nature of isoprenoids found in plants, emphasizing the wide range of physiological functions these compounds serve. The biosynthetic origins of isoprenoids have occupied chemists and biochemists for decades, and the second section of this review recaps some of the conceptual models used to rationalize key biosynthetic reactions in the isoprenoid pathway. The third section describes briefly some of the recently developed experimental systems that have helped researchers uncover much of the biochemistry and molecular biology of isoprenoids. The fourth section compares the deduced amino acid sequences of enzymes with similar catalytic functions and attempts to correlate these sequences with the known enzymol­ ogy. The fifth and final section focuses on our limited understanding of how

isoprenoid biosynthesis is regulated in plants. 

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Chemical Diversity and Defence Metabolism: How Plants Cope with Pathogens and Ozone Pollution

Chemical Diversity and Defence Metabolism: How Plants Cope with Pathogens and Ozone Pollution | PlantSterolMetabolism | Scoop.it

Abstract: Chemical defences represent a main trait of the plant innate immune system. Besides regulating the relationship between plants and their ecosystems, phytochemicals are involved both in resistance against pathogens and in tolerance towards abiotic stresses, such as atmospheric pollution. Plant defence metabolites arise from the main secondary metabolic routes, the phenylpropanoid, the isoprenoid and the alkaloid pathways. In plants, antibiotic compounds can be both preformed (phytoanticipins) and inducible (phytoalexins), the former including saponins, cyanogenic glycosides and glucosinolates. Chronic exposure to tropospheric ozone (O3) stimulates the carbon fluxes from the primary to the secondary metabolic pathways to a great extent, inducing a shift of the available resources in favour of the synthesis of secondary products. In some cases, the plant defence responses against pathogens and environmental pollutants may overlap, leading to the unspecific synthesis of similar molecules, such as phenylpropanoids. Exposure to ozone can also modify the pattern of biogenic volatile organic compounds (BVOC), emitted from plant in response to herbivore feeding, thus altering the tritrophic interaction among plant, phytophagy and their natural enemies. Finally, the synthesis of ethylene and polyamines can be regulated by ozone at level of S-adenosylmethionine (SAM), the biosynthetic precursor of both classes of hormones, which can, therefore, mutually inhibit their own biosynthesis with consequence on plant phenotype.

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Peroxisomal localisation of the final steps of the mevalonic acid pathway in planta - Springer

Peroxisomal localisation of the final steps of the mevalonic acid pathway in planta - Springer | PlantSterolMetabolism | Scoop.it

In plants, the mevalonic acid (MVA) pathway provides precursors for the formation of triterpenes, sesquiterpenes, phytosterols and primary metabolites important for cell integrity. Here, we have cloned the cDNA encoding enzymes catalysing the final three steps of the MVA pathway from Madagascar periwinkle (Catharanthus roseus), mevalonate kinase (MVK), 5-phosphomevalonate kinase (PMK) and mevalonate 5-diphosphate decarboxylase (MVD). These cDNA were shown to functionally complement MVA pathway deletion mutants in the yeast Saccharomyces cerevisiae. Transient transformations of C. roseus cells with yellow fluorescent protein (YFP)-fused constructs reveal that PMK and MVD are localised to the peroxisomes, while MVK was cytosolic. These compartmentalisation results were confirmed using the Arabidopsis thaliana MVK, PMK and MVD sequences fused to YFP. Based on these observations and the arguments raised here we conclude that the final steps of the plant MVA pathway are localised to the peroxisome.

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Systems Understanding of Isoprenoid Pathway Regulation in Arabidopsis - Springer

Systems Understanding of Isoprenoid Pathway Regulation in Arabidopsis - Springer | PlantSterolMetabolism | Scoop.it

Recent technological advancement in molecular biosciences makes it possible to study biological processes at the systems level. At present, two main biological systems approaches are recognized: top-down and bottom-up. Top-down approach uses the “omics” data to characterize the system in a comprehensive way. Result of this approach is a topological or phenomenological molecular network. A bottom-up approach, on the contrary, uses an already defined network and kinetic properties of the individual network components to build a model with the predictive value. Systems understanding of plant isoprenoid pathway regulation is at present largely dominated by top-down approaches, as building of a complete dynamic model of isoprenoid pathway regulation requires prior identification of all elements of the isoprenoid pathway network and an associated regulatory network. In this chapter, an overview is given on the progress in systems biology research on isoprenoid pathway in a model plantArabidopsis thaliana. First, an overview on existing resources to obtainArabidopsis isoprenoid pathway gene network is presented. Second, available methods to obtain quantitative “omics” data with the focus on isoprenoid pathway are discussed. And lastly, systems biology approaches and their application to isoprenoid pathway research are shown.

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Sterol Biosynthesis Inhibitors: Potential for Transition State Analogs and Mechanism-Based Inactivators Targeted at Sterol Methyltransferase - Springer

Sterol Biosynthesis Inhibitors: Potential for Transition State Analogs and Mechanism-Based Inactivators Targeted at Sterol Methyltransferase - Springer | PlantSterolMetabolism | Scoop.it

Sterol biosynthesis inhibitors (SBIs), discovered in the late 1960s and subsequently used commercially to treat ergosterol-dependent fungal diseases, represent a unique drug class targeted at an enzyme in a biosynthetic pathway. To date, few drugs have been commercialized as enzyme inhibitors; yet, prescription of SBIs has emerged as the gold standard for some cases of non-life-threatening antifungal chemotherapy and in crop protection. SBIs are not designed for their structural resemblance to the sterol molecule; they nonetheless can engender a curative effect by interfering with sterol production and homeostasis in the pathogenic organism. The increased use of SBIs in recent years, particularly the azole antifungals, has resulted in the development of resistance to those drugs, necessitating additional work to further our understanding of antifungal resistance and to explore opportunities to develop new enzyme inhibitors and uncover new enzyme targets that can regulate carbon flux in the post-lanosterol/cycloartenol pathway. This article reports general considerations for enzyme mechanism and active-site probes using inhibitors of the C-methylation reaction, including a potential new class of antifungal/antiparasitic agents of phytosterol synthesis tailored as mechanism-based inactivators. These steroid-based compounds prepared with different sterol side chain functionalities are designed to reversibly or irreversibly impair the sterol methyltransferase, an enzyme expressed in pathogenic microbes and plants but not in the human host. The salient aspects of these and related topics directed toward the enzyme recognition of sterol structure, and the inhibitory properties and catalytic competence of a series of specifically modified substrate analogs that affect sterol methyltransferase action are discussed.

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New aspects of sterol biosynthesis in growth and development of higher plants

New aspects of sterol biosynthesis in growth and development of higher plants | PlantSterolMetabolism | Scoop.it

The characterization of the enzymatic components of plant sterol biosynthesis, the phenotypic description of a set of Arabidopsis thaliana sterol mutants, and consequently, the identification of aspects of growth and development influenced by sterols have been in recent years a very fruitful area of research. The overall data obtained in the field have shown an essential role of sterols at the cellular level in hormone signaling, organized divisions and embryo patterning. Indeed, current research efforts strongly suggest that membrane bound proteins implicated in polarized auxin transport or ethylene signaling have altered activity or functionality in a modified sterolic environment.

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Subcellular evidence for the involvement of peroxisomes in plant isoprenoid biosynthesi

Subcellular evidence for the involvement of peroxisomes in plant isoprenoid biosynthesi | PlantSterolMetabolism | Scoop.it

The role of peroxisomes in isoprenoid metabolism, especially in plants, has been questioned in several reports. A recent study of Sapir-Mir et al.1 revealed that the two isoforms of isopentenyl diphosphate (IPP) isomerase, catalyzing the isomerisation of IPP to dimethylallyl diphosphate (DMAPP) are found in the peroxisome. In this addendum, we provide additional data describing the peroxisomal localization of 5-phosphomevalonate kinase and mevalonate 5-diphosphate decarboxylase, the last two enzymes of the mevalonic acid pathway leading to IPP.2 This finding was reinforced in our latest report showing that a short isoform of farnesyl diphosphate, using IPP and DMAPP as substrates, is also targeted to the organelle.3 Therefore, the classical sequestration of isoprenoid biosynthesis between plastids and cytosol/ER can be revisited by including the peroxisome as an additional isoprenoid biosynthetic compartment within plant cells.

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