Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Making a Friend from a Foe: Expressing a GroEL Gene from the Whitefly Bemisia tabaci in the Phloem of Tomato Plants Confers Resistance to Tomato Yellow Leaf Curl Virus
1 The Otto Warburg Minerva Center for Agricultural Biotechnology & The Robert H. Smith Institute for Plant Science and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel. Correspondence: akad@ufl.edu, Correspondence: czosnek@agri.huji.ac.il
2 UNESCO Biotechnology Center, Bethlehem University, Bethlehem, West Bank, Palestinian Authority
Breeding for virus resistance in transgenic crop plants is based on a variety of strategies such as expressing pathogen-derived genes or on RNA-mediated gene silencing. The strategy used in the present research is based on a totally new concept. It takes advantage of the fact that some, and perhaps all, plant viruses transmitted by their insect vectors in a circulative manner interact in the insect haemolymph with GroEL homologues produced by the vector endosymbiotic bacteria. It has been suggested that GroEL-virus interaction could be a mechanism shared by plant circulative viruses to avoid destruction in the haemolymph. In this study, we have exploited this phenomenon to generate transgenic tomato plants expressing the whitefly GroEL in their phloem. We expected that once inoculated by their vector, phloem-limited circulative viruses will be trapped by GroEL in the plant phloem, thereby inhibiting invasion of phloem-associated cells and long distance movement, rendering the plants resistant to the virus. A gene encoding a GroEL homologue from the whitefly B. tabaci was cloned in an Agrobacterium binary vector under the control of an Arabidopsis phloem-specific promoter, which was used to transform two tomato genotypes. GroEL was expressed in the two genotypes, during two consecutive generations. All the twenty four To GroEL-transgenic tomato plants obtained (but one and its progeny) exhibited good levels of resistance to whitefly-mediated inoculation of TYLCV, exhibiting mild or no disease symptoms. The transgenic progeny of the resistant plants expressed GroEL and were as resistant as their parents. Resistant plants of the To and T1 generations contained less viral DNA than susceptible non-transgenic plants. In T1 resistant plants, in vitro assays indicated that viral particles were complexed with GroEL in the plant sap. The mode of interaction between GroEL and TYLCV, the effect of this complex on the cell-to-cell and long-distance spread of the virus, and the mechanism by which resistance is established, remain to be investigated.