Common inheritance of chromosome Ia associated with clonal expansion of Toxoplasma gondii.
Toxoplasma gondii is a globally distributed protozoan parasite that can infect virtually all warm-blooded animals and humans. Despite the existence of a sexual phase in the life cycle, T. gondii has an unusual population structure dominated by three clonal lineages that predominate in North America and Europe, (Types I, II, and III). These lineages were founded by common ancestors approximately10,000 yr ago. The recent origin and widespread distribution of the clonal lineages is attributed to the circumvention of the sexual cycle by a new mode of transmission-asexual transmission between intermediate hosts. Asexual transmission appears to be multigenic and although the specific genes mediating this trait are unknown, it is predicted that all members of the clonal lineages should share the same alleles. Genetic mapping studies suggested that chromosome Ia was unusually monomorphic compared with the rest of the genome. To investigate this further, we sequenced chromosome Ia and chromosome Ib in the Type I strain, RH, and the Type II strain, ME49. Comparative genome analyses of the two chromosomal sequences revealed that the same copy of chromosome Ia was inherited in each lineage, whereas chromosome Ib maintained the same high frequency of between-strain polymorphism as the rest of the genome. Sampling of chromosome Ia sequence in seven additional representative strains from the three clonal lineages supports a monomorphic inheritance, which is unique within the genome. Taken together, our observations implicate a specific combination of alleles on chromosome Ia in the recent origin and widespread success of the clonal lineages of T. gondii.
Khan
Asis
A
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Böhme
Ulrike
U
Kelly
Krystyna A
KA
Adlem
Ellen
E
Brooks
Karen
K
Simmonds
Mark
M
Mungall
Karen
K
Quail
Michael A
MA
Arrowsmith
Claire
C
Chillingworth
Tracey
T
Churcher
Carol
C
Harris
David
D
Collins
Matthew
M
Fosker
Nigel
N
Fraser
Audrey
A
Hance
Zahra
Z
Jagels
Kay
K
Moule
Sharon
S
Murphy
Lee
L
O'Neil
Susan
S
Rajandream
Marie-Adele
MA
Saunders
David
D
Seeger
Kathy
K
Whitehead
Sally
S
Mayr
Thomas
T
Xuan
Xuenan
X
Watanabe
Junichi
J
Suzuki
Yutaka
Y
Wakaguri
Hiroyuki
H
Sugano
Sumio
S
Sugimoto
Chihiro
C
Paulsen
Ian
I
Mackey
Aaron J
AJ
Roos
David S
DS
Hall
Neil
N
Berriman
Matthew
M
Barrell
Bart
B
Sibley
L David
LD
Ajioka
James W
JW
D000818:Animals; D002875:Chromosomes; D003433:Crosses, Genetic; D019143:Evolution, Molecular; D014644:Genetic Variation; D005828:Genetics, Population; D040582:Inheritance Patterns; D008540:Meiosis; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D014122:Toxoplasma / Q000145:classification / Q000235:genetics*