The Vat locus encodes for a CC-NBS-LRR protein that confers resistance to Aphis gossypii infestation and A. gossypii-mediated virus resistance.

Aphis gossypii is a polyphagous sucking aphid and a vector for many viruses. In Cucumis melo, a dominant locus, Vat, confers a high level of resistance to Aphis gossypii infestation and to viruses transmitted by this vector. To investigate the mechanism underlying this double resistance, we first genetically dissected the Vat locus. We delimited the double resistance to a single gene that encodes for a coiled-coil-nucleotide-binding-site-leucine-rich repeat (CC-NBS-LRR) protein type. To validate the genetic data, transgenic lines expressing the Vat gene were generated and assessed for the double resistance. In this analysis, Vat-transgenic plants were resistant to A. gossypii infestation as well as A. gossypii-mediated virus transmission. When the plants were infected mechanically, virus infection occurred on both transgenic and non-transgenic control plants. These results confirmed that the cloned CC-NBS-LRR gene mediates both resistance to aphid infestation and virus infection using A. gossypii as a vector. This resistance also invokes a separate recognition and response phases in which the recognition phase involves the interaction of an elicitor molecule from the aphid and Vat from the plant. The response phase is not specific and blocks both aphid infestation and virus infection. Sequence analysis of Vat alleles suggests a major role of an unusual conserved LRR repeat in the recognition of A. gossypii.