Sugar transporter genes of the brown planthopper, Nilaparvata lugens: A facilitated glucose/fructose transporter Shingo Kikuta a, b , Takahiro Kikawada b , Yuka Hagiwara-Komoda b , Nobuhiko Nakashima b , Hiroaki Noda a, b, * a Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan b National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan article info Article history: Received 30 March 2010 Received in revised form 13 July 2010 Accepted 27 July 2010 Keywords: Sugar transporters Nilaparvata lugens EST Fructose Glucose abstract The brown planthopper (BPH), Nilaparvata lugens, attacks rice plants and feeds on their phloem sap, which contains large amounts of sugars. The main sugar component of phloem sap is sucrose, a disac- charide composed of glucose and fructose. Sugars appear to be incorporated into the planthopper body by sugar transporters in the midgut. A total of 93 expressed sequence tags (ESTs) for putative sugar transporters were obtained from a BPH EST database, and 18 putative sugar transporter genes (Nlst1e18) were identified. The most abundantly expressed of these genes was Nlst1. This gene has previously been identified in the BPH as the glucose transporter gene NlHT1 , which belongs to the major facilitator superfamily. Nlst1 , 4, 6, 9, 12, 16, and 18 were highly expressed in the midgut, and Nlst2, 7 , 8, 10, 15, 17, and 18 were highly expressed during the embryonic stages. Functional analyses were performed using Xenopus oocytes expressing NlST1 or 6. This showed that NlST6 is a facilitative glucose/fructose trans- porter that mediates sugar uptake from rice phloem sap in the BPH midgut in a manner similar to NlST1. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The brown planthopper (BPH) is the most serious insect pest of rice plants. It is a vascular feeder and transmits rice plant viruses, as well as causes severe damage when feeding (Hibino, 1996; Sogawa, 1982). The phloem sap in the vascular bundles of rice contains a considerable concentration of sugars, which are synthesized in the leaves and transferred to other tissues. These phloem sap sugars are a major energy source for the BPH (Sogawa, 1982). Elucidation of the mechanism of sugar uptake into the gut and hemolymph is important in order to understand energy acquisition in plant sap-feeding insects and to identify new targets for the control of these pests. Sugar transporters play an essential role in controlling carbo- hydrate transport in a diverse array of organisms, from bacteria to mammals, and are responsible for mediating the movement of sugars into cells (Mueckler, 1994). Two categories of sugar trans- porters are currently known; the facilitated sugar transporter and the Na þ /sugar symporter or H þ /sugar symporter (Wood and Trayhurn, 2003). The proteins of the facilitated sugar transporter family move sugars along gradients from regions of high concen- tration to those of lower concentration. The Na þ /sugar symporter or H þ /sugar symporter acts as a secondary active membrane transporter that moves sugars via electrochemical membrane gradients of Na þ or H þ ions, respectively. In the mammalian intestine, sugars are transported not only by facilitated transports but also by sodium-dependent glucose transporter in a process driven by an electrochemical membrane potential (Wright, 1993). Epithelial cells in the human small intestine take up sugars through the intestinal brush-border membrane via the sodium-dependent glucose transporter (SGLT1) and passively export the sugars through the basal membrane via facilitated sugar transporter 2 (GLUT2) (Drozdowski and Thomson, 2006; Wright et al., 2007). If these sugar transporters are deficient, the result is a disease involving glucose-galactose malabsorption. Sugar transporters may offer a new potential target for the control of insect pests. However, relatively little information is currently available on insect sugar transporters (Burchmore et al., 2003; Chen et al., 2006; Caccia et al., 2007; Kikawada et al., 2007; Price et al., 2007b, 2010; Kanamori et al., 2010). The sugar trans- porter NlHT1 , which was previously identified in the BPH, is a facilitative glucose transporter and is specifically expressed in the midgut (Price et al., 2007b). Other sugar transporters are also expected to be present and to function in the gut of the BPH for the * Corresponding author. National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan. Tel.: þ81 29 838 6109; fax: þ81 29 838 6028. E-mail address: hnada@affrc.go.jp (H. Noda). Contents lists available at ScienceDirect Insect Biochemistry and Molecular Biology journal homepage: www.elsevier.com/locate/ibmb 0965-1748/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibmb.2010.07.008 Insect Biochemistry and Molecular Biology 40 (2010) 805e813