Isoprenoid generating systems in plants — A handy toolbox how to assess contribution of the mevalonate and methylerythritol phosphate pathways to the biosynthetic process

Abstract

Isoprenoids comprise an astonishingly diverse group of metabolites with numerous potential and actual applications in medicine, agriculture and the chemical industry. Generation of efficient platforms producing isoprenoids is a target of numerous laboratories. Such efforts are generally enhanced if the native biosynthetic routes can be identified, and if the regulatory mechanisms responsible for the biosynthesis of the compound(s) of interest can be determined.

In this review a critical summary of the techniques applied to establish the contribution of the two alternative routes of isoprenoid production operating in plant cells, the mevalonate and methylerythritol pathways, with a focus on their co-operation (cross-talk) is presented. Special attention has been paid to methodological aspects of the referred studies, in order to give the reader a deeper understanding for the nuances of these powerful techniques. This review has been designed as an organized toolbox, which might offer the researchers comments useful both for project design and for interpretation of results obtained.

Introduction

Plants exhibit a remarkably high level of biochemical complexity and flexibility which, despite their sessile lifestyle, allows them to survive in different environments and quickly adapt to various fluctuating conditions. This metabolic plasticity is to great extent achieved due to the isoprenoids, the most structurally and functionally diverse class of plant natural products which includes essential primary metabolites (e.g., phytosterols, chlorophylls, ubiquinone) as well as a broad range of functional secondary metabolites. These specialized natural products play a vital role in plant adaptive responses to biotic and abiotic stress, attract pollinators, repel predators, modulate allelopathic interactions (e.g. isoprene, monoterpenes, diterpenes). Isoprenoids exert either synergistic (photosynthetic pigments) or antagonistic (phytohormones: gibberrelins and cytokinins) effects in cellular processes. Some isoprenoids are produced constitutively (e.g. phytosterols) while synthesis of others is induced upon particular cues such as wounding, attack of predator, elicitation or upon elevated concentration of methyl jasmonate (e.g., sesquiterpenoids, triterpenoids). All these features add up to the exquisite modulatory potential of the so-called plant terpenome [1]. Evidently, to fully exploit this prospective, the plant cell requires precise and strictly regulated metabolic network.

The use of plant isoprenoids as pharmaceuticals, fragrances, flavours, colorants, and dietary supplements (Fig. 1) makes them the most commercially exploited group of plant-derived natural products with the market worth millions of dollars. Those economically priceless isoprenoids are present in plant tissues in rather small amounts and their acquisition from natural resources is in most cases very expensive, insufficient and may pose a threat for biodiversity (e.g. isolation of paclitaxel from Pacific yew). Therefore, unraveling the isoprenoid biosynthetic network is not only of interest for basic studies but also benefits and stimulates the construction of efficient platforms for their production [2]. Indeed, the continuously increasing number of articles published in this field illustrates how much attention it receives (for example [3], [4], [5], [6], [7], with totally over 30 reviews and more than 100 experimental papers, focused on isoprenoids biosynthesis, published in 2014, according to PubMed).