MOLECULAR CHARACTERIZATION OF SPIROPLASMA-CITRI BR3 LINES THAT DIFFERIN TRANSMISSIBILITY BY THE LEAFHOPPER CIRCULIFER TENELLUS

Four lines of Spiroplasma citri strain BR3, derived from different mai ntenance conditions over several years and differing in their ability to be transmitted by the beet leafhopper Circulifer tenellus were char acterized. The lines included BR3-T (transmissible), maintained in tur nip by leafhopper transmission; BR3-G (now nontransmissible), maintain ed in plants by periodic graft transmission; BR3-P (now rarely transmi ssible), subcultured in artificial medium over 130 times; and BR3-M (t ransmissible), subcultured 43 times. Although all four lines had simil ar overall protein profiles, the two transmissible lines each containe d two proteins missing in the non- or rarely transmitted lines. In add ition, one protein was unique to BR3-M and another was unique to BR3-P . Spiralin, a major S. citri membrane protein, had dual mobility in li ne BR3-G only. Patterns of extrachromosomal DNA and restricted total D NA also were similar, although differences occurred among the four lin es. The genome of line BR3-G was larger than those of the other lines and unique restriction bands occurred in this line. Protein and DNA pr ofiles of six to eight individual clones of each line also were compar ed. Protein patterns within each clone were indistinguishable except f or a difference in the migration rate of spiralin in clones of BR3-G. Restricted total DNA showed differential patterns among clones of each line, possibly reflecting differences in extrachromosomal DNA. Molecu lar differences among the spiroplasma lines may reflect the selection pressures of the different environments in which they were maintained and suggest genes and proteins that may be involved in the biological phenotypes of these lines.