Evolutionary origin and establishment of a dioecious diploid-tetraploid complex

Area of Science:

• Plant evolutionary biology
• Genomics
• Reproductive biology

Background:

• Polyploid emergence is common in angiosperms, but establishment is challenging due to minority cytotype exclusion.
• Dioecious (having separate sexes) plants may face unique challenges in polyploid establishment.
• This study investigates factors facilitating the establishment of dioecious polyploids.

Purpose of the Study:

• To test if a stable sex-determination system and spatial/ecological isolation aid dioecious polyploid establishment.
• To understand the origin and evolutionary history of polyploids in Salix polyclona.

Main Methods:

• Ploidy level determination in 351 individuals from 28 Salix polyclona populations.
• Resequencing of 190 individuals for genomic diversity and phylogenetic analyses.
• K-mer spectra analysis for polyploid origin determination and sex-determination factor identification.

Main Results:

• 52% of Salix polyclona individuals were tetraploids, suggesting an autopolyploid origin.
• A female heterogametic sex-determining factor on chromosome 15 was identified in diploids, likely conserved in tetraploids.
• Tetraploids exhibited distinct geographic distribution in western/central China and emerged 7.6-2.3 million years ago.

Conclusions:

• Inheritance of a stable sex-determination system (intrinsic factor) and spatial isolation (extrinsic factor) likely facilitated the establishment of dioecious polyploid populations.
• Geological and climatic history influenced polyploid emergence and demographic patterns.
• Findings provide insights into polyploid establishment mechanisms in dioecious species.