title: Genome structure and emerging evidence of an incipient sex chromosome in Populus.
abstract: The genus Populus consists of dioecious woody species with largely unknown genetic mechanisms for gender determination. We have discovered genetic and genomic features in the peritelomeric region of chromosome XIX that suggest this region of the Populus genome is in the process of developing characteristics of a sex chromosome. We have identified a gender-associated locus that consistently maps to this region. Furthermore, comparison of genetic maps across multiple Populus families reveals consistently distorted segregation within this region. We have intensively characterized this region using an F(1) interspecific cross involving the female genotype that was used for genome sequencing. This region shows suppressed recombination and high divergence between the alternate haplotypes, as revealed by dense map-based genome assembly using microsatellite markers. The suppressed recombination, distorted segregation, and haplotype divergence were observed only for the maternal parent in this cross. Furthermore, the progeny of this cross showed a strongly male-biased sex ratio, in agreement with Haldane's rule that postulates that the heterogametic sex is more likely to be absent, rare, or sterile in interspecific crosses. Together, these results support the role of chromosome XIX in sex determination and suggest that sex determination in Populus occurs through a ZW system in which the female is the heterogametic gender.
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Tongming
authors.initials: T
authors.lastname: Yin
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Difazio
authors.forename: Lee E
authors.initials: LE
authors.lastname: Gunter
authors.forename: Xinye
authors.initials: X
authors.lastname: Zhang
authors.forename: Michell M
authors.initials: MM
authors.lastname: Sewell
authors.forename: Scott A
authors.initials: SA
authors.lastname: Woolbright
authors.forename: Gery J
authors.initials: GJ
authors.lastname: Allan
authors.forename: Collin T
authors.initials: CT
authors.lastname: Kelleher
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Douglas
authors.forename: Mingxiu
authors.initials: M
authors.lastname: Wang
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Tuskan
mesh_terms: D002874:Chromosome Mapping; D032461:Chromosomes, Plant; D018745:Genome, Plant; D032107:Populus / Q000235:genetics*; D011995:Recombination, Genetic; D012730:Sex Chromosomes; D019849:Sex Determination Processes