Sequence analysis of two plasmids from the phytoplasma beet leafhopper-transmitted virescence agent

Abstract

The complete nucleotide sequences of the two plasmids from the phytoplasma beet leafhopper-transmitted virescence agent (BLTVA) have been determined. The larger plasmid, pBLTVA-1, was 10 785 nt in length and contained 11 putative ORFs, almost all of which were duplicated or triplicated on the plasmid due to the presence of large repeated regions. The sequence contained a series of tandem repeats, the largest of which was 338 nt long. The sequences of ORFs 4 and 11 showed homology with the replication genes of plasmids from other phytoplasmas and from geminiviruses. ORF9, the only ORF present as a single copy, showed homology with DNA primase genes from bacterial chromosomes and contained the conserved zinc finger and topoisomerase/primase domains. None of the other eight ORFs showed homology with known sequences in the GenBank database. pBLTVA-2 was 2587 nt in length, and all of its sequence was nearly identical to sequences from pBLTVA-1, most of which spanned ORFs 10 and 11, including the 338 nt tandem repeat. Analysis of 30 strains of BLTVA showed that most of the 11 putative ORFs were present, but the size of the plasmids varied in these strains.

Living with Genome Instability: the Adaptation of Phytoplasmas to Diverse Environments of Their Insect and Plant Hosts

“…There is high variability of the occurrence of ORFs in the plasmids of 30 beet leafhopper-transmitted virescence phytoplasma strains (55). There is also evidence of intramolecular recombination among phytoplasma plasmids (55,73). We show that they can also recombine with the chromosome (Fig.…”

“…1B) (73), and the plasmids of beet leafhoppertransmitted virescence phytoplasma range from ϳ2.5 to ϳ11 kb (55). There is high variability of the occurrence of ORFs in the plasmids of 30 beet leafhopper-transmitted virescence phytoplasma strains (55). There is also evidence of intramolecular recombination among phytoplasma plasmids (55,73).…”

“…Geminivirus-like repA genes in OY-M (75) and more distantly related phytoplasmas (55,81) were also identified. Like phytoplasmas, geminiviruses are insect-transmitted plant pathogens and have to pass through the gut epithelium, hemolymph, and salivary gland cells of the insect vectors before returning to the plant (22).…”

“…OY-M has plasmids ranging from ϳ3 to ϳ7 kb in size (Fig. 1B) (73), and the plasmids of beet leafhoppertransmitted virescence phytoplasma range from ϳ2.5 to ϳ11 kb (55). There is high variability of the occurrence of ORFs in the plasmids of 30 beet leafhopper-transmitted virescence phytoplasma strains (55).…”

“…We identified four plasmids in AY-WB. Plasmids have been detected in a number of other phytoplasmas (55,73). Each AY-WB plasmid contains two genes involved in rolling-circle amplification and two to six ORFs with unknown function, several of which were predicted to target the AY-WB membrane, suggesting that the plasmids are involved in AY-WB association with the plant and insect hosts.…”