Host plant adaptation in Plutellid moths
Final Report Abstract
The factors that determine host plant specificity and host range of insect herbivores are incompletely understood: Why do herbivorous insects feed on some plant species and not on others? Why do some insects have a broad host range while close relatives have a narrow host range? Which factors determine host plant specificity and host plant range? Biochemical adaptations of herbivores to overcome host plant chemical defenses are crucial for host plant colonization. Here, we chose the association of moths of the Plutellidae family with host plants chemically defended by the glucosinolate-myrosinase system as an example to address these questions. The most prominent species in this family is the cabbage moth (Plutella xylostella), a devastating pest on crops from the Brassicaceae family. The larvae of this species convert glucosinolates very quickly to harmless desulfoglucosinolates by gutexpressed glucosinolate sulfatases (GSS) and, thus, circumvent toxic effects derived from the glucosinolate-myrosinase system. The three known GSS of P. xylostella differ in their substrate specificity and inducibility. Together, they reflect the very broad host plant range of the insect. While P. xylostella has been subject of much research, the other more than 50 Plutellid species from five genera have not been investigated with respect to their adaptational mechanisms, but most of them feed on Brassicales. However, in contrast to the polyphagous P. xylostella, other glucosinolate-feeding Plutellids are oligo- or monophagous, i.e., they have few or even only a single reported host species. In this project, we investigated the presence, biochemical capacities, and evolutionary history of GSS in the Plutellidae in relation to natural variation in defensive chemistry among their host plants. We analyzed >300 field-collected host plant leaf samples, generated near-complete genome sequences of five Plutellid species representing four genera, expressed 26 GSS heterologously and compared their activity towards 21 glucosinolates. We found that all major Plutellid genera possess GSS1 and GGS3 with distinct biochemical properties and that GSS genes have a monophyletic origin in the Plutellidae. This indicates that GSS represent the major biochemical mechanism of larval host plant adaptation in all glucosinolate-feeding Plutellidae. GSS substrate spectra of one species covered all glucosinolates present in its host plants, but did not exactly match the host plants' glucosinolate profiles. Phytochemical analyses of Plutellid host plants identified several new chemotypes. Total glucosinolate content varied largely between and within host plant species and may pose a challenge even to specialized herbivores. The phylogeny of Plutellid GSS turned out to be rather complex, and its interpretation requires further analyses.
Publications
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Host plant adaptation in Plutellid moths – Do glucosinolate spectra of host plants determine host plant range? International Conference of the German Society of Plant Sciences, Bonn
Pormetter L., Pfalz M., Kroymann J., Vogel H. & Wittstock U.
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Host plant adaptation in Plutellid moths - Do glucosinolate sulfatase specificities match host plant glucosinolate spectra? Symposium on Insect-Plant Relationships, Bielefeld, poster P3-07
Pormetter L., Pfalz M., Kroymann J., Voge, H. & Wittstock U.
