W636 Rapid divergence and expansion of X chromosome in papaya

Date: Sunday, January 15, 2012
Time: 5:30 PM
Room: Royal Palm Salon 5-6
Andrea Gschwend , University of Illinois at Urbana-Champaign, Urbana, IL
Qingyi Yu , Texas A&M University, Weslaco, TX
Ray Ming , University of Illinois at Urbana - Champaign, Urbana, IL
The majority of sex chromosome studies focus on the rapidly evolving hemizygous Y chromosome, while the X chromosome has been assumed to retain the ancestral autosome content and structure.  The recently evolved X chromosome of trioecious Carica papaya differs significantly from the ancestral autosome, as detected through a direct comparison with the orthologous autosome of monoecious Vasconcellea monoica, a close relative of papaya.  The accumulation of LTR retroelements has led to a substantial expansion in the papaya X-specific region.  The gene density of papaya X-specific region is nearly 3 times less than that of the corresponding region in V. monoica and the gene content is rather diverse compared to the autosomal region, where the gene number and order are conserved.   Genes have been gained, lost, and rearranged between the X specific region of papaya and the corresponding region of V. monoica.  Interestingly, the genes with alleles shared between the papaya X and papaya HSY (male-specific region of the Yh chromosome) have diverged similarly from the gene copy on the orthologous chromosome of V. monoica.  The repetitive element content of the BACs lends strong support to the location of the centromere being present in the X-specific region, a centromeric location which appears to be conserved between papaya and V. monoica.  The papaya X chromosome has evolved considerably since the suppression of recombination between the X and the HSY and is not necessarily an accurate representative of the ancestral autosome.