Beet curly top virus symptom amelioration in Nicotiana benthamiana transformed with a naturally occurring viral subgenomic DNA.

Beet curly top virus (BCTV) infection is associated with the de novo synthesis of a heterogeneous population of subgenomic viral DNAs. Nicotiana benthamiana plants transformed with a partial repeat of one such subgenomic DNA remain susceptible to infection but produce ameliorated symptoms when agroinoculated with BCTV. Transgenic plants contained from 10 to 30% of the amount of viral DNA detected in nontransformed control plants showing severe symptoms. Symptom amelioration is associated with the mobilization of subgenomic DNA from the integrated template and its amplification to approximately one third of the total amount of viral DNA. The amplification in transgenic plants of a specific subgenomic DNA rather than a heterogeneous population implies that mobilization from the integrated template frequently occurs during systemic infection, precluding the accumulation of other subgenomic DNA forms.