Sulfur-Containing Secondary Metabolites and Their Role in Plant Defense

Abstract

Although sulfur-containing products of secondary metabolism are rather unusual plant constituents, they play an important role in plant–pest interactions in a variety of different plant families and constitute major chemical defenses in the Brassicaceae, Alliaceae and Asteraceae. Besides their role as key players in two activated plant defense systems, the glucosinolate–myrosinase system of the Brassicaceae and the alliin–alliinase system of the Alliaceae, sulfur-containing compounds include prominent phytoalexins with structures ranging from elemental sulfur to the alkaloid-like camalexin and complex polypeptides like the defensins. Due to the diversity in chemical structures and modes of action, sulfur-containing natural products provide plants with a versatile array of chemical defenses against a broad range of potential enemies. The use of the model plant Arabidopsis thaliana has considerably advanced our understanding of the biochemistry of several classes of these compounds including the glucosinolates, camalexin and the defensins at the molecular level. This has paved the way for metabolic engineering projects aimed at elucidating the ecological roles of sulfur-containing defenses as well as at improving the nutritional value and pest resistance of crop plants.