Pathogen-derived resistance to Citrus tristeza virus (CTV) in transgenic Mexican lime (Citrus aurantifolia (Christ.) Swing.) plants expressing its p25 coat protein gene

The p25 coat protein (CP) gene of Citrus tristeza virus (CTV) was incorporated to Mexican lime plants and forty-two transgenic lines were produced, 25 containing the p25 CP gene of the severe CTV strain T-305 and 17 with that of the mild strain T-317. When plants propagated from each transgenic line were graft-inoculated with CTV T-305 or aphidinoculated with T-300, two types of response to viral challenge were observed: some lines developed CTV symptoms similar to those of non-transgenic controls, whereas others exhibited protection against the virus. This protection consisted of a proportion of plants, ranging from 10 to 33%, that were resistant to CTV, and the rest of them that showed a significant delay in virus accumulation and symptom onset. Protection was efficient against non-homologous CTV strains and was generally accompanied by high accumulation of p25 CP in the protected lines, which suggest a CP-mediated protection mechanism in most cases. This is the first report demonstrating pathogen-derived resistance in transgenic plants against a Closterovirus member in its natural host.