Convergent Patterns of Karyotype Evolution Underlying Karyotype Uniformity in Conifers

Area of Science:

• Plant genomics
• Evolutionary biology
• Cytogenetics

Background:

• Karyotype diversity is crucial for speciation, yet gymnosperms, especially conifers, show significant karyotype uniformity.
• Understanding the evolutionary mechanisms behind this uniformity is key to explaining conifer diversification.

Purpose of the Study:

• To reconstruct the karyotype evolutionary history of gymnosperms using comparative genomic analyses.
• To identify the primary mechanisms driving karyotype evolution and uniformity in conifers.

Main Methods:

• Comparative genomic analyses, including synteny analysis, were performed.
• Graph-based methods were used to infer evolutionary pathways from ancestral to modern karyotypes.
• Reciprocal translocation patterns were analyzed across conifer genomes.

Main Results:

• Conifers lack ancient polyploidy, and it is rare in gymnosperms overall.
• Convergent patterns of reciprocal translocations, particularly centromeric-centromeric reciprocal translocations (CRTs), are prevalent in conifer genomes.
• Telomeric-centromeric reciprocal translocations (TRTs) were identified as significant in descending dysploidy within Cupressales.
• Evolutionary pathways from a proto-gymnosperm karyotype (n=12) to modern conifer karyotypes (n=11-12) were inferred.

Conclusions:

• The scarcity of polyploidy and dysploidy contributes to gymnosperm karyotype uniformity and potentially lower species richness compared to angiosperms.
• Pervasive CRTs and occasional TRTs explain this apparent uniformity, supporting the karyotype orthoselection hypothesis.
• This research provides novel insights into karyotype evolution mechanisms that maintain uniformity in conifers and influence their diversification.