A possible role of CTV.20 gene methylation in response to Citrus tristeza virus infection

Citrus tristeza virus (CTV) is the pathogen causing tristeza diseases in several Rutaceae species and leading to significant economic damage to citrus worldwide. The Ctv locus provides broad spectrum resistance to CTV in Poncirus trifoliata L. Raf. This locus is present also in tolerant and susceptible species, so an epigenetic mechanism of Ctv expression regulation was proposed. Indeed, a difference in plant 24-nt sRNAs distribution corresponding to CTV.20 gene was previously observed in susceptible species following CTV infection. This gene, encoding for a plant virus movement-like protein, was investigated as a candidate gene for CTV susceptibility. Here, we show the presence of differences in methylation status of a specific region of CTV.20 in two susceptible species, sour and sweet orange, following CTV infection. On the contrary, no significant differences were observed in the tolerant Citrange carrizo following the infection. Moreover, a hypermethylation of the whole CTV.20 gene was observed in Citrange carrizo both healthy and infected, and in healthy sour and sweet orange. This preliminary study allows hypothesizing a possible role of methylation in regulation of CTV.20 expression involved in the CTV susceptibility.