Conventional breeding of citrus types demands a long-term effort due to their complex reproductive biology and long juvenile period. As a compelling alternative, genetic engineering of mature tissues allows the insertion of specific traits into specific elite cultivars, including well-known and widely grown varieties and rootstocks, thus reducing the time and costs involved in improving and evaluating them. Conventional breeding for resistance to CTV in citrus varieties has been largely unsuccessful as well as cloning of the genes conferring resistance to specific citrus types. RNA interference (RNAi), based on producing dsRNAs (usually using intron-hairpin constructs) highly homologous to specific CTV sequences to trigger RNA silencing, has been employed to produce virus-resistant transgenic citrus plants. The most successful construct has been an intron-hairpin vector carrying full-length, untranslatable versions of the genes p25, p20, and p23 from the virus. Using it, we have generated full resistance against CTV in Mexican lime. Moreover, this strategy is applicable to all those citrus varieties amenable to mature transformation, including sweet oranges, sour oranges, mandarins, Citrus macrophylla, and limes.
Keywords: Citrus; Genetic engineering; In vitro culture; Mature tissue transformation; RNA silencing; Virus resistance.