Research Scientist HHMI Janelia Research Campus Ashburn, Virginia
In an extreme form of interspecies exploitation, insects hijack plant development to induce novel plant organs called galls which provide the insect with a nutritious home. Galls represent a dramatic reprogramming of plant cell biology resulting from the direct action of insects on host plants. Here, I will talk about galls induced by the aphid, Hormaphis cornu, on the leaves of Hamamelis virginiana. We disvovered that the galling generation of this aphid produces a large class (~500) of novel secreted, cysteine-rich proteins with no homology to any known proteins. These proteins are highly divergent other than a pair of widely spaced cysteine-tyrosine-cysteine (CYC) motifs, hence named bicycle proteins. One of the bicycle genes, dgc, is genetically linked to a naturally occuring variation in gall color. Furthurmore, this aphid genotype has a specific effect on plant gene expression providing evidence for bicycle genes as effectors in aphid gall development. Our studies indicate that the transformation of leaf tissue into a gall is driven by the direct action of injected aphid bicycle proteins.
