A divergent RWP-RK transcription factor determines mating type in heterothallic Closterium

Area of Science:

• Evolutionary biology
• Algal genetics
• Reproductive biology

Background:

• The Closterium peracerosum-strigosum-littorale complex (Zygnematophyceae) exhibits an isogamous mating system.
• Zygnematophyceae are the closest relatives to land plants, making their reproductive mechanisms crucial for evolutionary studies.
• Genetic determination of mating type (MT) is known in related chlorophytic algae.

Purpose of the Study:

• To investigate the genetic basis of mating type determination in Closterium.
• To identify the specific gene responsible for the mt- mating type phenotype.

Main Methods:

• Genome sequencing of mt+ and mt- strains of Closterium.
• Identification and functional analysis of candidate genes using reverse genetics.
• Gene knockout and heterologous expression experiments.

Main Results:

• A gene, CpMinus1, was identified and linked to the mt- mating type.
• CpMinus1 encodes a transcription factor specifically expressed during gamete differentiation.
• Introduction of CpMinus1 converted an mt+ strain to mt-, and knockout of CpMinus1 in mt- strains resulted in an mt+ phenotype.

Conclusions:

• CpMinus1 is proposed as the primary determinant of the mt- mating type in Closterium, suppressing the mt+ phenotype.
• The findings suggest independent evolution of this mating determinant in the Zygnematophyceae lineage.
• The mating type locus in Closterium may involve mt- specific regions with limited recombination.