Symbionts associated with the salivary glands of the potato leafhopper, Empoasca fabae, and their function when feeding on leguminous hosts

Abstract

Many species of phloem feeding insects are host to symbiotic bacteria, which provide their hosts with nutrients lacking from phloem. The potato leafhopper, <italic>Empoasca fabae</italic>, feeds on the phloem and cell contents of a wide variety of plants. In this study, I identified two taxa of symbiotic bacteria present in the salivary glands, midgut, bacteriomes and saliva of the potato leafhopper: <italic>Sulcia muelleri</italic> and <italic>Wolbachia</italic>. Treatment of the leafhoppers with 0.01% oxytetracycline-HCl resulted in the creation of aposymbiotic leafhoppers. Longevity and fecundity of aposymbiotic leafhoppers on alfalfa, <italic>Medicago sativa</italic>, and fava bean, <italic>Vicia faba</italic>, were significantly lower than that of symbiotic leafhoppers. In addition, aposymbiotic leafhoppers caused less of a decrease in photosynthesis rates on both alfalfa and fava bean in comparison to symbiotic leafhoppers. The salivary gland transcriptome of the potato leafhopper revealed the presence of potential salivary components, including lipase, pectin lyase and alkaline phosphatase, all of which were expressed at higher levels in salivary glands than in midgut or hind femur tissue. In addition, transcripts attributed to <italic>Wolbachia</italic> were discovered in the sialotranscriptome, providing more evidence that this bacterium is present in the salivary glands of the potato leafhopper. Finally, expression of alfalfa wound response genes after exposure to potato leafhopper saliva was measured. Endo 1-3 ß-D-glucanase, isoflavone reductase, chalcone synthase and phenylalanine ammonia-lyase gene expression were higher in plants exposed to leafhopper saliva than in unexposed controls. Treatment of saliva with heat, filter sterilization, DTT, EDTA and K₂HPO₄ led to different plant wound response gene expression patterns. I conclude that the symbionts present in the potato leafhopper are necessary for the normal development and reproduction of this species, in addition to playing a potential role in plant wound response to feeding.