I’ve have always been fascinated by the existence of specific biochemicals that that significantly govern interactions between organisms. Plants, arthropods and microbes are the most species rich life forms on earth. As primary producers, photosynthetic organisms are the ultimate source of most fixed carbon and under significant pressure to relinquish these resources. For reproductive success, plants must balance both growth and defense against a myriad of herbivorous arthropods and pathogens. These real-time interactions are of relevance to our global food supply and are underpinned by genetics, biochemistry, physiology, and behavior.
We utilize maize (Zea mays) and bean (Phaseolus & Vigna spp.) to examine dynamic inducible innate immune responses that limit losses against attacking organisms. In response to herbivory by generalist lepidopteran pests, plants rapidly initiate the biosynthesis and release of low molecular weight Volatile Organic Compounds (VOCs). Prominent in this VOC signature are monoterpenes, homoterpenes and sesquiterpenes that serve as indirect plant defenses by enabling the attraction of predators, parasitioids, and other natural enemies. How is this process enabled? We examine the mechanistic role of exogenous elicitors, termed Herbivore Associated Molecular Patterns (HAMPs), and endogenous signal transduction cascades that regulate insect-induced plant responses.
In contrast to foliar herbivores, maize fungal pathogens elicit the biosynthesis of non-volatile acidic terpenoid phytoalexins with direct antibiotic activity. The most highly inducible transcripts following pathogen attack encode the β-macrocarpene synthases (ZmTps) 6/11 and the ent-copalyl diphosphate synthase termed Anther Ear 2 (ZmAn2). Down stream predicted enzymatic products of ZmTps6/11 and ZmAn2, termed zealexins and kauralexins respectively, are the predominant phytoalexins of mature maize plants. These recent discoveries raise many questions including: what exogenous and endogenous signals strongly promote maize phytoalexin biosynthesis? What are the roles of these terpenoids in plant protection? plant signaling? rhizosphere interactions? allelopathy? autotoxicity? and human health? Given that approximately 150,000 square of maize is annually planted in the U.S. and that fungal attack is aggressive during senescence it is of interest to know, where do these compounds go? what is their fate in the environment?
We utilize biochemical discovery approaches based on the coupling of separations with rapid activity based bioassays, NMR structure elucidation, mass spectrometry for the plant metabolomic analyses of novel induced defenses and signals, genetic resources to test candidate pathways, global expression analyses for co-regulated processes, expression quantitative trait loci (eQTL) for gene discovery, transient and heterologous expression of enzymes for product analyses, and other tools to uncover previously hidden pathways and mechanisms underlying plant-mediated interactions with their biotic and abiotic environment.
Eric Schmelz completed his PhD within the Center for Insect Science/Plant-Insect Interactions Group at the University of Arizona, Tucson. He then carried out his postdoctoral and research scientist studies at the USDA-Agricultural Research Service located at the University of Florida, Gainesville. He joined the Division of Biological Sciences faculty at U.C. San Diego in July 2014.