SUMMARY

ic virus (BDMV) are phylogenetically related, bipartite-genome begomoviruses. AbMV is limited to the plant host phloem but BDMV is not. We have previously pro-vided evidence that the genomic DNA-A component of BDMV contains determinants involved in movement (Levy and Czosnek, 2003). We report here that the DNA-A-encoded genes AC2 and AC3 are involved in virus accumulation and spread. To follow AbMV and BDMV movement in inoculated bean plants, we re-placed their coat protein genes (CP) with DNA encod-ing the green or the red fluorescent proteins (GFP, RFP) to create BDMV-CP:GFP, BDMV-CP:RFP, and AbMV-CP:GFP. Frame-shift mutations in BDMV AC2 and AC3 to produce BDMV-CP:GFP-mC23 resulted in inhibition of BDMV movement when co-inoculated with BDMV DNA-B. The mutation reverted to wild-type and movement was restored when BDMV-CP:GFP-mC23 was co-inoculated with BDMV-CP:RFP and BDMV DNA-B, which strongly suggests that the AC2/AC3 region is important for BDMV movement. Consequently we replaced the AC2/AC3 region of Ab-MV-CP:GFP with that of BDMV to create AbMV-CP:GFP-C23: BDMV. AbMV-CP: GFP-C23: BDMV inoculated together with AbMV DNA-B moved from cell to cell in the epidermis towards the phloem, and long-distance in the entire plant, even though inocula lacked part of all of BDMV DNA-B. AbMV-CP:GFP with its cognate DNA-B was unable to move. Inocula-tion of bean with AbMV-CP:GFP-C23:BDMV and BD-MV DNA-B resulted in the accumulation of very large amounts of viral DNA, in remarkably fast systemic movement, and in the early appearance of severe symp-toms, which in most cases, resulted in an inhibition of germination. These results suggest that interactions be-tween AC2/AC3 of BDMV and other proteins encoded by AbMV DNA-A and DNA-B influence the ability o