Asparagus officinalis XX female PacBio sequencing

The origin of sex chromosomes has been hypothesized to involve the linkage of factors with antagonistic effects on male and female function. Garden asparagus (Asparagus officinalis L.) is an ideal species to test this hypothesis, as the X and Y chromosomes are cytologically homomorphic and evolved from an ancestral autosome pair in association with a shift from hermaphroditism to dioecy. Here we generate a PacBio XX female PacBio genome assembly for comparison against the Y chromosome. Comparison of contiguous X and Y chromosome assemblies shows that hemizygosity underlies the loss of recombination between the genes suppressing female organogenesis (SUPPRESSOR OF FEMALE FUNCTION, SOFF) and promoting male function (TAPETAL DEVELOPMENT AND FUNCTION1, aspTDF1). These findings provide direct evidence that sex chromosomes can function through linkage of two sex determination genes.