Functional equivalence of late gene promoters in bean golden mosaic virus with those in tomato golden mosaic virus

In the bipartite geminivirus tomato golden mosaic virus (TGMV), the activit y of late gene promoters is up-regulated by the multifunctional viral prote in AL2, Cis-acting sequences required for AL2-mediated promoter responses h ave not been well characterized. However, nucleotide sequence analysis has implicated a motif termed the conserved late element (CLE), The CLE is pres ent in TGMV and many other begomoviruses, although it is not ubiquitous. He re we analysed the regulation of late gene expression in bean golden mosaic virus (BGMV), one of the begomoviruses which lacks the CLE. Transient repo rter gene assays showed that BGMV late gene promoters were trans-activated in Nicotiana benthamiana protoplasts, both by the homologous BGMV AL2 prote in and by the heterologous TGMV AL2 protein. The BGMV AL2 protein also tran s-activated TGMV late gene promoters, Consistent with these results, we fou nd that hybrid viruses with the late gene promoters exchanged between BGMV and TGMV were viable in planta.