Resistance to Tomato Yellow Leaf Curl Virus by Combining Expression of a Natural Tolerance Gene and a Dysfunctional Movement Protein in a Single Cultivar

Background The tomato yellow leaf curl disease (TYLCV) has been a major deterrent to tomato production in Israel for the last 20 years. This whitefly-transmitted viral disease has been found in the Caribbean Island in the early 1990s, probably as an import from the Middle East. In the late 1990s, the virus has spread to the US and is now conspicuous in Florida and Georgia. Objectives Because of the urgency facing the TYLCV epidemics, there was a compelling need to mobilize scientists to develop tomato variety resistant to TYLCV. The major goal was to identify the virus movement protein (MP) and to express a defective from of MP in a cultivar that contained the natural Ty-1 resistance gene. The research included 1. cloning of the TYLCV isolate from the Dominican Republic (DR) which is (or a close variant) also present in the continental USA; 2. ddefining the role of the MP; 3. mutating the putative MP gene; 4. introducing the modified gene into an advance Ty-1 line; 5. testing the transgenic plants in the field. The pressing threat to tomato production in the US resulted in an extension of the objectives: more emphasis was placed on characterization of TYLCV i the DR, on determination of the epidemiology of the virus in the DR, and on using new TYLCV resistance sources for tomato breeding. Achievements and signification 1. The characterization of TYLCV-DR allowed for more effective TYLCV management strategies that are now implemented in the DR. 2. The identification of the TYLCV MPs and, more importantly, insight into their function has provided a model for how these proteins function in TYLCV movement and support the targeting of one or more of these proteins in a dominant lethal strategy to engineer plants for TYLCV resistance. 3. The transgenic plants that are being generated with wild-type and mutated TYLCV MPs will serve to test the hypothesis that interference with one or more of the TYLCV movement proteins will be a strategy for generating TYLCV-resistant plants. 4. The fine mapping of the resistance Ty-1 gene allowed eliminating deleterious chromosome segments from the wild tomato genitor L. chilense. It may in a near future allow the cloning of the first geminivirus resistance gene. 5. Another resistance source from the wild tomato species L. hirsitum was introgressed into the domesticated tomato, resulting in the production of resistant breeding lines. Implications 1. The monitoring of TYLCV in whiteflies has been applied in the DR. These tools are presently being used to assist in the evaluation of the host-free period and to help select the appropriate locations for growing tomatoes in the DR. 2. An overall strategy to obtain resistance against TYLCV has been used. The expression of wild-type or mutated TYLCV MPs in transgenic tomato is another addition to the arsenal used to fight TYLCV, together with marker assisted breeding and mobilization of additional resistant genes from the wild.