Schematic diagrams of the transformation vector and experimental procedure. (A) Selection of three DNA fragments targeting different viral genomic regions. (B) The three fragments were ligated and assembled into a sequence which, when transcribed, would produce a hairpin RNAi structure. Arrows indicate the orientation of each fragment in the hairpin structure. (C) Schematic diagram of the structural features of the inducible pX9- hpICMV RNAi construct and Cre/loxP-mediated DNA recombination (Zuo et al. Guo et al. ,). Cre, the bacteriophage P1 Cre recombinase with an intron; Frag, fragment; Hpt, a hygromycin-resistance marker gene driven by nopaline synthase (nos) promoter (Pnos); ICMV, Indian cassava mosaic virus; loxP, specific recognition sites of Cre; OlexA-46, eight copies of the LexA DNA-binding site fused to the −46 CaMV 35S promoter; XVE, a chimeric transactivator containing the regulator domain of an estrogen receptor. Arrows inside transcription units indicate the direction of transcription. P1 to P4 denote primers used for PCR analysis to a detect recombination event for Hpt selection marker excision shown in Figure 2. (D) A flowchart of experimental procedure for screening virus resistance transgenic events by Agrobacterium-mediated infection.