Grant: Discovery Grants Program - Individual

Mechanisms and dynamics of herbivore adaptation to their host plant are fundamental to understanding the basis and the evolution of plant-herbivore interactions. Adaptive steps leading to the formation of host-specialized populations have been dissected in both generalist and specialist herbivores. However, the mechanisms and the effectiveness of initial adaptation that enables a herbivore to shift to a new plant host toward the evolution of ecological speciation is poorly understood. The two spotted spider mite Tetranychus urticae (TSSM) is a herbivore that can feed on an extremely wide range of plants. Individual mite populations have a narrower range of hosts but can adapt in ~25 generations to initially unfavorable plants. The long-term goal of this program of research is to understand the mechanisms of mite adaptation to plant hosts. In the last 5 years, my team: a) used an experimental evolutionary setup to adapt a bean (Phaseolus vulgaris)-adapted population to Arabidopsis; b) identified at least two distinct classes of JA-regulated Arabidopsis resistance traits against spider mite herbivory; one class of these metabolites are indole glucosinolates; the second class are other MYC2,3,4-regulated defenses that are currently not known; c) performed comparative RNASeq analysis of mite populations that have differential susceptibilities to Arabidopsis defenses; d) initiated the analysis of indole glucosinolate breakdown products that have miticidal activity. This work led to a groundbreaking discovery of indole glucosinolate-dependent cyanide release that protects Arabidopsis against mite herbivory and the constitutive upregulation of the b-cyanoalanine synthase that enables Arabidopsis-adapted mites to counter cyanide toxicity. In the next 5 years, we will address following research objectives: Dissection of the complexity of Arabidopsis defenses against TSSM Using genetics (mutants in genes encoding biosynthesis of candidate defense metabolites), biochemical (targeted and untargeted plant metabolomics) and toxicological analysis (TSSM dose responses to individual metabolites), we will identify metabolites with acaricidal properties and will characterize their mode of action against TSSM. Identification of TSSM mechanisms that counteract Arabidopsis defenses Using RNAi as a reverse genetics tool, metabolomic analysis of mite extracts upon mite exposure to plant xenobiotic compounds and the analysis of recombinant mite proteins and their activities, we will determine genes and enzymes that are required for mite adaptation to Arabidopsis. This multidisciplinary approach will establish an unprecedented level of understanding of plant herbivore interaction, contributing to fundamental knowledge. The proposed research will also enable an outstanding training of HQPs creating experts with cutting edge skills in the highly valued area of agrigenomics and crop protection, in addition to transferable skills in commercialization, IP and communication.