Evidence of intermolecular recombination between extrachromosomal DNAs in phytoplasma: a trigger for the biological diversity of phytoplasma?
Recombination among bacterial extrachromosomal DNAs (EC-DNAs) plays a major evolutionary role by creating genetic diversity, and provides the potential for rapid adaptation to new environmental conditions. Previously, a 7 kbp EC-DNA, EcOYW1, with a geminivirus-like rolling-circle-replication protein (Rep) gene was isolated and characterized from an original wild-type line (OY-W) of onion yellows (OY) phytoplasma, an endocellular cell-wall-less prokaryote that inhabits the cytoplasm of both plant and insect cells. EcOYW1, found in OY-W, was not present in a mild-symptom line (OY-M) derived from OY-W. A 4 kbp EC-DNA, pOYW, was also isolated and characterized from OY-W, and its pLS1-plasmid-like rep gene was expressed. This paper describes the isolation and sequencing of an EC-DNA of 5560 nt, EcOYW2, from OY-W, and its counterpart EC-DNA of 5025 nt, EcOYM, from OY-M. EcOYW2 and EcOYM contained seven and six ORFs, respectively. They both encoded a geminivirus-like Rep and a putative single-stranded-DNA-binding protein (SSB). Southern blot analysis indicated that no more EC-DNAs with a rep gene exist in either OY-W or OY-M, which means that the complete set of EC-DNAs has been cloned from the OY-W and OY-M lines of OY phytoplasmas. Sequence analysis revealed that both EcOYW2 and EcOYM have chimeric structures of previously characterized EcOYW1 and pOYW, suggesting that they have a recombinational origin. This is the first evidence of intermolecular recombination between EC-DNAs in phytoplasma. The possible implications of these findings in increasing the biological diversity of phytoplasma are discussed.
Nishigawa
Hisashi
H
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan1.
Oshima
Kenro
K
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan2.
Kakizawa
Shigeyuki
S
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan2.
Jung
Hee-Young
HY
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan1.
Kuboyama
Tsutomu
T
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan1.
Miyata
Shin-Ichi
SI
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan2.
Ugaki
Masashi
M
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan2.|Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan1.
Namba
Shigetou
S
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan2.|Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan1.
D000595:Amino Acid Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics; D004261:DNA Replication / Q000235:genetics; D004277:DNA, Single-Stranded / Q000235:genetics; D004268:DNA-Binding Proteins; D005798:Genes, Bacterial / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010944:Plants / Q000382:microbiology; D010957:Plasmids / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D008973:Tenericutes / Q000737:chemistry / Q000166:cytology* / Q000235:genetics*; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics
D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D015534:Trans-Activators; C045264:replication initiator protein; D004265:DNA Helicases