FIG 6.

Model illustrating the putative origins of recent recombination events (solid arrows) and horizontal gene transfers (dotted arrows) leading to the emergence of X. perforans SC3 to SC6, along with the corresponding host range. The thickness of the arrows showing recent recombination is proportional to the overall amount of sequence donated to each X. perforans lineage. The specific genes or functional pathways associated with recombination/horizontal-transfer events are labeled where available; Xps TIISS, Xps type II secretion system; TonB, TonB transduction system; xopE3^Tnp, xopE3 disrupted by a transposon insertion; avrBsT-like, putative type 3 secreted effector gene with 71% amino acid identity to AvrBsT. The chromosomes (ovals) and plasmids (smaller circles) of donor lineages are color coded accordingly. We currently do not know if the pthXp1 gene was acquired via plasmid or Tn3-like transposase-mediated horizontal transfer or the origin of this novel transcription activation-like effector. A question mark was placed after the host range of SC4, as pathogenicity to pepper has been documented experimentally for only one strain from the group (22).