Department of Entomology

Abstract: Plants show considerable within-species variation in their susceptibility to insect herbivores. In the case of Zea mays (maize) infested with Rhopalosiphum maidis (corn leaf aphid), there is 100-fold range in aphid progeny production on different inbred lines. Benzoxazinoids, a class of secondary metabolites found in many grasses, are known to influence herbivore resistance. Comparison of aphid resistance and benzoxazinoid content in 25 maize inbred lines associated improved aphid growth with a high ratio of HDMBOA-Glc (2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside) to DIMBOA-Glc (2,4-dihy¬droxy-7-methoxy-1,4-benzoxazin-3-one gluco¬side). Genetic mapping identified quantitative trait loci (QTL) influencing both maize aphid resistance and benzoxazinoid content. Co-localization of these QTL, identification of candidate genes in the maize genome, demonstration of DIMBOA-Glc methyltransferase activity in vitro, and the discovery of a natural gene-inactivating transposon insertion show that high DIMBOA-Glc methyltransferase activity decreases maize aphid resistance. This is a notable contrast to prior experiments showing increased resistance to lepidopteran herbivores through induced methylation of DIMBOA-Glc to make HDMBOA-Glc. Thus, there are ecological tradeoffs in the production of these defensive secondary metabolites in maize.
Host: Steve Whitham
Sponsored by PSI Virus-Insect Interactions Initiative and PSI Approaching Crops as Ecosystems