A sucrose-specific receptor in Bemisia tabaci and its putative role in phloem feeding

Abstract

In insects, specialized feeding on the phloem sap (containing mainly the sugar sucrose) has evolved only in some hemipteran lineages. This feeding behavior requires an ability to locate feeding sites buried deeply within the plant tissue. To determine the molecular mechanism involved, we hypothesized that the phloem-feeding whitefly <i>Bemisia tabaci</i> relies on gustatory receptor (GR)-mediated sugar sensing. We first conducted choice assays, which indicated that <i>B. tabaci</i> adults consistently choose diets containing higher sucrose concentrations. Next, we identified four <i>GR</i> genes in the <i>B. tabaci</i> genome. One of them, <i>BtabGR1</i>, displayed significant sucrose specificity when expressed in <i>Xenopus</i> oocytes. Silencing of <i>BtabGR1</i> significantly interfered with the ability of <i>B. tabaci</i> adults to discriminate between non-phloem and phloem concentrations of sucrose. These findings suggest that in phloem feeders, sugar sensing by sugar receptors might allow tracking an increasing gradient of sucrose concentrations in the leaf, leading eventually to the location of the feeding site.