Differential resistance to Citrus psorosis virus in transgenic Nicotiana benthamiana plants expressing hairpin RNA derived from the coat protein and 54K protein genes.

Citrus psorosis virus (CPsV), genus Ophiovirus, family Ophioviridae, is the causal agent of a serious disease affecting citrus trees in many countries. The viral genome consists of three ssRNAs of negative polarity. Post-transcriptional gene silencing (PTGS), a mechanism of plant defence against viruses, can be induced by transgenic expression of virus-derived sequences encoding hairpin RNAs. Since the production of transgenic citrus lines and their evaluation would take years, a herbaceous model plant, Nicotiana benthamiana, was used to test hairpin constructs. The expression of self-complementary hairpin RNA fragments from the coat protein (cp) and 54K genes of the Argentine CPsV 90-1-1 isolate conferred resistance on N. benthamiana plants, indicating that these constructs are good candidates for the transformation of citrus plants. The degree of resistance obtained varied depending on the viral sequence chosen. The analysis of the levels of small interfering RNA accumulation and viral RNAs indicated that the construct derived from cp gene was better at inducing PTGS than that originating from the 54K gene. The dependence of PTGS induction on the degree of identity between the target and the inducer transgene sequences was tested using sequences derived from CPV4, a more distant isolate of CPsV, as PTGS targets. Efficient silencing induction was also obtained to this isolate through the expression of the cp-derived hairpin. This is the first report of transgenic-resistant plants within the context of this serious citrus disease.