Ac. Padovan et al., Chromosome mapping of the sweet potato little leaf phytoplasma reveals genome heterogeneity within the phytoplasmas, MICROBIO-UK, 146, 2000, pp. 893-902
To further understand the genomic diversity and genetic architecture of phy
toplasmas, a physical and genetic map of the sweet potato little leaf (SPLL
) strain V4 phytoplasma chromosome was determined. PFGE was used to determi
ne the size of the SPLL-V4 genome, which was estimated to be 622 kb. A phys
ical map was prepared by two-dimensional reciprocal digestions using the re
striction endonucleases BssHII. SmaI. EagI and I-CeuI, Sixteen cleavage sit
es were located on the map. Southern hybridizations of digested SPLL-V4 chr
omosomal DNA were done using random clones and PCR-amplified genes as probe
s. This confirmed fragment positions and located the two rRNA operons and t
he linked fus/tuf genes encoding elongation factors G and Tu. respectively,
on the physical map. An inversion of one of the rRNA operons was observed
from hybridization data. Sequence analysis of one of the random clones iden
tified a gid gene encoding a glucose-inhibited division protein. Digestions
of the tomato big bud (TBB) phytoplasma chromosome with the same four enzy
mes revealed genome heterogeneity when compared to the closely related SPLL
-V4, and a preliminary chromosome size for the TBB phytoplasma of 662 kb wa
s estimated. This mapping information has revealed that significant genome
diversity exists within the phytoplasmas.