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Abstract Detail

Comparative Genomics/Transcriptomics

Harkess, Alex [1], Leebens-Mack, Jim [2], Meyers, Blake [1], Huang, Kun [3], Batish, Mona [3].

Testing a "two gene" model for sex chromosome evolution in asparagus.

An elegant model for the conversion of an autosomal pair in a hermaphroditic species to a sex chromosome in a dioecious species was formalized by Deborah and Brian Charlesworth in 1978. Briefly, the conversion from autosome to sex chromosome could require just two loci linked perfectly in non-recombination on a young Y chromosome: one locus must dominantly suppress female (pistil) organogenesis, while another locus must promote the formation of male (anther) organogenesis, but this model has never had strong genic support in any dioecious species. Garden asparagus (Asparagus officinalis) is an ideal system to test this question, given that the X and Y sex chromosomes are evolutionarily young and cytologically homomorphic. Leveraging a doubled haploid YY individual and a doubled haploid mapping population, we generated a chromosome-level genome assembly using Illumina, PacBio, and Bionano optical maps and identified a 1Mb region of non-recombination on the Y chromosome that is largely missing from the X. Several independent male-to-hermaphrodite mutants (gamma irradiation, spontaneous SNP) implicate a single gene SOFF (Suppressor of Female Function) on the Y chromosome as being responsible for female suppression. While only 12 gene annotations are in this non-recombining region, there exists Tapetum Development and Function 1, a gene with an Arabidopsis knockout phenotype very similar to Asparagus females. EMS mutagenesis confirms that tdf1 knockouts are neuters. With an additional PacBio and optical map genome assembly for a sibling XX female, we have compared the structure of the X and Y chromosomes and identified ~130kb of X-specific sequence, including several X-specific genes. Further, single molecule FISH (sm-FISH) was used to quantify individual mRNAs and visualize the precise developmental expression patterns of both SOFF and TDF1 along a spear tip gradient. Additionally, an in-progress Oxford Nanopore genome for a hermaphroditic individual is being generated to determine the ancestral autosome sequence. This is the strongest evidence to date for the Charlesworth's "two gene" model.

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1 - Donald Danforth Plant Science Center
2 - University of Georgia, Plant Biology, Athens, GA
3 - University of Delaware, Neward, DE

Sex chromosomes

Presentation Type: Oral Paper
Session: 25, Comparative Genomics and Transcriptomics II
Location: 102/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 2:30 PM
Number: 25007
Abstract ID:769
Candidate for Awards:Margaret Menzel Award

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