Abstract:
Xanthomonas vasicola pathovar vasculorum (Xvv) is the bacterial agent causing
gumming disease in sugarcane. Here, we compare complete genome sequences for five
isolates of Xvv originating from sugarcane and one from maize. This identified two distinct
types of lipopolysaccharide synthesis gene clusters among Xvv isolates: one is similar to
that of Xanthomonas axonopodis pathovar citri (Xac) and is probably the ancestral type,
while the other is similar to those of the sugarcane-inhabiting species, Xanthomonas
sacchari. Four of six Xvv isolates harboured sequences similar to the Xac plasmid,
pXAC47, and showed a distinct Type-IV pilus (T4P) sequence type, whereas the T4P locus
of the other two isolates resembled that of the closely related banana pathogen,
Xanthomonas campestris pathovar musacearum (Xcm). The Xvv isolate from maize has lost
a gene encoding a homologue of the virulence effector, xopAF, which was present in all
five of the sugarcane isolates, while xopL contained a premature stop codon in four out of six isolates. These findings shed new light on evolutionary events since the divergence of
Xvv and Xcm, as well as further elucidating the relationships between the two closely
related pathogens.