Breaking linkage between mating compatibility factors: Tetrapolarity in Microbotryum

Area of Science:

• Evolutionary Biology
• Genetics
• Mycology

Background:

• Sexual eukaryotes typically link genes for self-incompatibility to balance reproductive assurance and recombination.
• Tetrapolarity (independent segregation of mating factors) is ancestral in Basidiomycetes, with transitions to bipolarity (linked factors) observed.
• The genus Microbotryum provides a unique system to study mating-type evolution and linkage dynamics.

Purpose of the Study:

• To report the first instance of linkage breakdown between self-incompatibility factors in Microbotryum.
• To investigate the genomic changes associated with the evolution of a tetrapolar breeding system from a bipolar ancestor.
• To understand how mating system dynamics, such as automixis, interact with linkage changes.

Main Methods:

• Comparative genomics to analyze genome structure alterations.
• Analysis of mating-type chromosome pairs and their structural dimorphism.
• Investigation of breeding system transitions and their impact on outcrossing rates.

Main Results:

• Demonstrated the breaking of linkage between two haploid self-incompatibility factors in Microbotryum.
• Identified major genome structure alterations, with compatibility factors on separate, reduced mating-type chromosome pairs.
• Observed that the automictic mating system may overcome reproductive assurance challenges posed by unlinked factors.

Conclusions:

• This study presents the first evidence of linkage breakdown leading to a tetrapolar system in Microbotryum.
• The findings suggest that mating system evolution can be influenced by changes in linkage of mating-type genes.
• This work challenges conventional views on mating-type evolution and the interplay between linkage and sexual reproduction.