Figure 5

GRD5 integrated into the Nicotiana genome after the divergence of N. otophora (a), presumably by illegitimate recombination with a free-living geminivirus (Ashby et al, 1997). The sequence became methylated, amplified and diversified into the GRD5 family before there was further Tomentosae speciation. After divergence within N. tomentosiformis (b), another family evolved, probably via a second independent integration event involving another geminivirus, an endogenous Helitron and GRD5, to form the GRD3 family at a second chromosomal locus. This line of N. tomentosiformis went on to form tobacco (c), on hybridisation and allopolyploidy involving N. sylvestris.