Abstract
BACKGROUND: Sex chromosomes often evolve faster than autosomes and commonly degenerate after recombination arrest. However, the underlying evolutionary processes are under persistent debate. In particular, it is unclear whether or not recombination arrest generally evolves in a stepwise manner and how switches in sex determination genes contribute to sex chromosome evolution. Here, we investigate sex chromosome evolution in the dioecious plant genus Salix. RESULTS: We identify Z- and W-regions (~ 8 Mb) on chromosome 15 of the dwarf willow Salix herbacea using a new haplotype-resolved assembly. The W-region harbours a large (5 Mb) embedded inversion. Analyses of synteny with other Salix species, sequence divergence between sex chromosomes and sequence degeneration suggest that this inversion recently incorporated pseudoautosomal sequence into the W-region, extending its length nearly three-fold. The W-region exclusively contains seven pairs of inverted partial repeats of the male essential floral identity gene PISTILLATA, suggesting a possible PISTILLATA suppression mechanism by interfering RNA in females. Such PISTILLATA pseudogenes are also found in other Salix species with ZW sex determination but not in those with XY sex determination. CONCLUSIONS: Our study provides rare and compelling support for the long-standing theory of inversions underlying stepwise recombination reduction and raises the hypothesis that the turnover of sex chromosomes in the Salicaceae family might be associated with a switch of the sex determination gene.
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Claims 6
Claim · model-written summary
Salix herbacea has approximately 8 Mb Z and W regions on chromosome 15.
- Taxon
- Salix herbacea
Salix herbaceae0 - Organ / stage
- chromosome 15e0
- Outcome
- Z- and W-regionse0
- Value
- ~ 8 Mbe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We identify Z- and W-regions (~ 8 Mb) on chromosome 15 of the dwarf willow Salix herbacea using a new haplotype-resolved assembly.”
Claim · model-written summary
The W region contains an embedded 5 Mb inversion.
- Taxon
- Salix herbaceaSalix herbaceae1
- Outcome
- embedded inversione0
- Value
- 5 Mbe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The W-region harbours a large (5 Mb) embedded inversion.”
t0“Sex chromosome evolution mediated by a large inversion and a possible switch of the sex determination gene”
e1“We identify Z- and W-regions (~ 8 Mb) on chromosome 15 of the dwarf willow Salix herbacea using a new haplotype-resolved assembly.”
Claim · model-written summary
The inversion appears to have recently incorporated pseudoautosomal sequence, nearly tripling the W region.
- Taxon
- Salix herbaceaSalix herbaceae1
- Organ / stage
- W-regione0
- Outcome
- extending its lengthe0
- Direction
- extendinge0
- Value
- nearly three-folde0
- Qualifier
- pseudoautosomal sequencee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this inversion recently incorporated pseudoautosomal sequence into the W-region, extending its length nearly three-fold.”
t0“Sex chromosome evolution mediated by a large inversion and a possible switch of the sex determination gene”
e1“We identify Z- and W-regions (~ 8 Mb) on chromosome 15 of the dwarf willow Salix herbacea using a new haplotype-resolved assembly.”
Claim · model-written summary
The W region uniquely contains seven pairs of inverted partial PISTILLATA repeats.
- Taxon
- Salix herbaceaSalix herbaceae1
- Gene
- PISTILLATAe0
- Outcome
- inverted partial repeatse0
- Value
- seven pairse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The W-region exclusively contains seven pairs of inverted partial repeats of the male essential floral identity gene PISTILLATA”
t0“Sex chromosome evolution mediated by a large inversion and a possible switch of the sex determination gene”
e1“We identify Z- and W-regions (~ 8 Mb) on chromosome 15 of the dwarf willow Salix herbacea using a new haplotype-resolved assembly.”
Claim · model-written summary
PISTILLATA pseudogenes occur in ZW Salix species.
SalixOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Such PISTILLATA pseudogenes are also found in other Salix species with ZW sex determination”
Claim · model-written summary
PISTILLATA pseudogenes were absent from XY Salix species.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but not in those with XY sex determination.”
t0“Sex chromosome evolution mediated by a large inversion and a possible switch of the sex determination gene”
e1“Such PISTILLATA pseudogenes are also found in other Salix species with ZW sex determination”