Abstract
Glucosinolates are an important class of secondary metabolites in Brassicales plants with a critical role in chemical defense. Glucosinolates are chemically inactive but can be hydrolyzed by myrosinases to produce a range of chemically active compounds toxic to herbivores and pathogens, thereby constituting the glucosinolate–myrosinase defense system or the mustard oil bomb. During the evolution, Brassicales plants have developed not only complex biosynthetic pathways for production of a large number of glucosinolate structures but also different classes of myrosinases that differ in catalytic mechanisms and substrate specificity. Studies over the past several decades have made important progress in the understanding of the cellular and subcellular organization of the glucosinolate–myrosinase system for rapid and timely detonation of the mustard oil bomb upon tissue damage after herbivore feeding and pathogen infection. Progress has also been made in understanding the mechanisms that herbivores and pathogens have evolved to counter the mustard oil bomb. In this review, we summarize our current understanding of the function and organization of the glucosinolate–myrosinase system in Brassicales plants and discuss both the progresses and future challenges in addressing this complex defense system as an excellent model for analyzing plant chemical defense.
Highlights
Published: 29 January 2022Plants have a variety of inducible and constitutive mechanisms including chemical defenses to protect themselves against attack by pathogens and herbivores
Upon tistissue damage by pests, glucosinolates are hydrolyzed by thioglucoside glucohydrolases sue damage by pests, glucosinolates are hydrolyzed by thioglucoside glucohydrolases (TGGs) called myrosinases into unstable thiohydroximate- O-sulfonates, which can rear(TGGs) called myrosinases into unstable thiohydroximate- O-sulfonates, which can rerange to form a range of hydrolytic products including isothiocyanates, nitriles, and other arrange to form a range of hydrolytic products including isothiocyanates, nitriles, and by-products toxic to herbivores, pathogens, and other organisms [12] (Figure 1)
In Arabidopsis seedlings, on the other hand, high levels of atypical myrosinases PYK10/BGLU23 and related β-glucosidase accumulate in the endoplasmic reticulum (ER)-derived organelles called ER bodies and can obtain access to the glucosinolates stored in the vacuole in the same cell upon tissue damage, enabling a single-cell chemical defense system [47,48]
Summary
Plants have a variety of inducible and constitutive mechanisms including chemical defenses to protect themselves against attack by pathogens and herbivores. Phytoanticipins are preformed antimicrobial compounds that are present in plants before attack by microorganisms or infection [7] Many of these antimicrobial chemicals are effective against other types of organisms including herbivores and, the classification of defense chemicals can be broadened to include those that respond to insect pests. Upon tistissue damage by pests, glucosinolates are hydrolyzed by thioglucoside glucohydrolases sue damage by pests, glucosinolates are hydrolyzed by thioglucoside glucohydrolases (TGGs) called myrosinases into unstable thiohydroximate- O-sulfonates, which can rear(TGGs) called myrosinases into unstable thiohydroximate- O-sulfonates, which can rerange to form a range of hydrolytic products including isothiocyanates, nitriles, and other arrange to form a range of hydrolytic products including isothiocyanates, nitriles, and by-products toxic to herbivores, pathogens, and other organisms [12] (Figure 1).
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