Chromosome sizes of phytoplasmas composing major phylogenetic groups

anglais. Chromosome sizes of 76 phytoplasmas belonging to 12 major phylogenetic groups were estimated from electrophoretic mobilities of full-length chromosomes in pulsed-field gels. Considerable variation in genome size, from 660 to 1,130 kb, was observed among aster yellows phytoplasmas. Chromosome size heterogeneity was also observed in the stolbur phytoplasma group, range 860 to 1,350 kb; in this group isolate STOLF contains the largest chromosome found in a phytoplasma to date. A wide range of chromosome sizes, from 670 to 1,075 kb, was also identified in the X-disease group. The other phytoplasmas examined, which included members of the apple proliferation, Italian alfalfa witches' broom, faba bean phyllody, pigeon pea witches' broom, sugarcane white leaf, Bermuda grass white leaf, ash yellows, clover proliferation and elm yellows groups, all have chromosomes smaller than 1,000 kb, and the size range within each of these groups is narrower than in the aster yellows, stolbur and X-disease groups. The smallest chromosome, about 530 kb, was found in two Bermuda grass white leaf phytoplasma isolates. This not only is the smallest mollicute chromosome found to date, but also is the smallest chromosome known for any cell

italien. [Sono state stimate le dimensioni del cromosoma di 76 fitoplasmi appartenenti ai 12 principali gruppi filogenetici mediante le mobilita' elettroforetiche dei cromosomi di lunghezza piena in campo pulsato. E' stata osservata una variabilita' considerevole, da 660 a 1.130 kb, nell'ambito dei fitoplasmi aster yellows. E' stata osservata un'eterogeneita' nella dimensione del cromosoma pure nel gruppo stolbur, con una variazione da 860 a 1.350 kb; in questo gruppo l'isolato STOLF contiene il cromosoma piu' grande riscontrato finora in un fitoplasma. Un'ampia variabilita' delle dimensioni del cromosoma, da 670 a 1.075 kb, e' riscontrata anche nel gruppo X-disease. Gli altri fitoplasmi esaminati, che comprendevano membri dei gruppi apple proliferation, Italian alfalfa witches' broom, faba bean phyllody, pigeon pea witches' broom, sugarcane white leaf, Bermuda grass white leaf, ash yellows, clover proliferation e elm yellows, presentano cromosomi piu' piccoli di 1.000 kb, e la variazione delle dimensioni nell'ambito di ognuno di questi gruppi e' minore di quella riscontrata nei gruppi aster yellows, stolbur e X-disease. Il cromosoma piu' piccolo, circa 530 kb, e' stato individuato in due isolati di fitoplasmi Bermuda grass white leaf. Questo non e' soltanto il cromosoma piu' piccolo di mollicuti identificato finora, ma anche il piu' piccolo cromosoma al momento conosciuto per qualsiasi tipo di cellula]