title: Phytoplasma PMU1 exists as linear chromosomal and circular extrachromosomal elements and has enhanced expression in insect vectors compared with plant hosts.
abstract: Phytoplasmas replicate intracellularly in plants and insects and are dependent on both hosts for dissemination in nature. Phytoplasmas have small genomes lacking genes for major metabolic pathways. Nevertheless, their genomes harbour multicopy gene clusters that were named potential mobile units (PMUs). PMU1 is the largest most complete repeat among the PMUs in the genome of Aster Yellows phytoplasma strain Witches' Broom (AY-WB). PMU1 is c. 20 kb in size and contains 21 genes encoding DNA replication and predicted membrane-targeted proteins. Here we show that AY-WB has a chromosomal linear PMU1 (L-PMU1) and an extrachromosomal circular PMU1 (C-PMU1). The C-PMU1 copy number was consistently higher by in average approximately fivefold in insects compared with plants and PMU1 gene expression levels were also considerably higher in insects indicating that C-PMU1 synthesis and expression are regulated. We found that the majority of AY-WB virulence genes lie on chromosomal PMU regions that have similar gene content and organization as PMU1 providing evidence that PMUs contribute to phytoplasma host adaptation and have integrated into the AY-WB chromosome.
authors.affiliation: Department of Entomology, The Ohio State University-Ohio Agricultural Research and Development Center (OARDC), Wooster, OH 44691, USA.
authors.forename: Tania Y
authors.initials: TY
authors.lastname: Toruño
authors.forename: Martina Seruga
authors.initials: MS
authors.lastname: Musić
authors.forename: Silvia
authors.initials: S
authors.lastname: Simi
authors.forename: Mogens
authors.initials: M
authors.lastname: Nicolaisen
authors.forename: Saskia A
authors.initials: SA
authors.lastname: Hogenhout
mesh_terms: D000818:Animals; D001483:Base Sequence; D002876:Chromosomes, Bacterial / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics*; D004270:DNA, Circular / Q000235:genetics; D018628:Gene Dosage; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D007313:Insecta / Q000382:microbiology; D020071:Interspersed Repetitive Sequences; D008969:Molecular Sequence Data; D005810:Multigene Family; D045582:Phytoplasma / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D010944:Plants / Q000382:microbiology; D014774:Virulence
chemical_list: D004269:DNA, Bacterial; D004270:DNA, Circular