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Abstract Detail

The evolutionary causes and consequences of dioecy across the land plants

Harkess, Alex [1], Leebens-Mack, Jim [1].

Sex-specific gene expression in dioecious Asparagus lineages.

The recent evolution of dioecy in garden asparagus (Asparagus officinalis) provides an emerging model system for investigating the origin and early evolution of sex chromosomes. In garden asparagus, sex determination is mediated by a small (<2 megabase) non-recombining locus that we have mapped to a pair of homomorphic X and Y incipient sex chromosomes. Species phylogenies reveal that a single transition from hermaphroditism to dioecy occurred less than 2 million years ago. The recent evolution of a non-recombining region on the Y chromosome in Asparagus is further substantiated by the viability of YY genotypes, referred to as “super males” in the asparagus breeding community. We are exploiting the recent origin of dioecy in Asparagus to directly test the “two locus” model of sex chromosome evolution proposed by Brian and Deborah Charlesworth in 1978 (Am. Nat. 112: 975-997). Asparagus serves as a particularly tractable model system for the evolution of sex chromosomes given its peculiar floral development patterns. In A. officinalis, developing flowers from XY/YY male and XX female sex genotypes are both initially hermaphroditic. In XY and YY male genotypes, the stylar tube quickly fails to develop, leaving behind only a small ovary in an otherwise functioning male flower. Developmentally later in XX females, anther development arrests with the breakdown of the tapetum before sporogenous cells can undergo meiosis. This temporal separation of male and female organ degeneration suggests that at least two genes are involved, consistent with a “two locus” model. To identify transcripts associated with sex genotype, we conducted RNA-Seq transcript profiling for XX, XY, and YY genotypes in four A. officinalis breeding lines. Transcriptome assembly and differential expression analysis reveals among-line variation in expression profiles and male-biased gene expression. As expected, a number of genes exhibiting male-biased expression are involved in the anther development pathway, and we are currently mapping candidates to identify their position relative to the sex determination region on the Y chromosome. Paired with an ongoing draft YY genome assembly, analyses of the RNA-Seq data have implicated a suite of genes that may be involved in gender determination. These candidates will be investigated further as we work to test the “two locus” model for the conversion of autosomes to sex chromosomes.

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1 - University of Georgia, 4503 Miller Plant Sciences, Athens, GA, 30602, USA

sex chromosomes

Presentation Type: Symposium or Colloquium Presentation
Session: SY05
Location: Jasperwood/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 3:15 PM
Number: SY05004
Abstract ID:353
Candidate for Awards:None

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