Protoplasmic Incompatibility in PODOSPORA ANSERINA: a Possible Function for Incompatibility Genes
1Laboratoire de Génétique, Allée des Facultés, 33405 Talence, France.
Abstract:
The suppression of protoplasmic incompatibility resulting from nonallelic gene interactions has been obtained by the coupled effect of mutations in the modA and modB genes (Bernet 1971). Due to their female sterility, modA modB strains provide an experimental tool to determine whether or not the mod and incompatibility loci are involved in a function other than protoplasmic incompatibility. Present results show that modA modB female sterility is a nonautonomous trait since heterokaryotic mycelia that include a modA modB nucleus and a female fertile nucleus (wild-type, modA or modB) produce modA modB protoperithecia, which are also formed by culture on medium supplemented with specific amino acids. Using modA modB strains, which are sterile at 32 degrees and fertile at 26 degrees , we have shown that the mod genes have no specific sequential timing. Indeed, the mod mutations may prevent the achievement of the female sexual cycle at any developmental stage from before early differentiation of protoperithecia until ascospore maturation. Employing different modA and modB mutations, we have shown that protoperithecia in modA modB cultures are generally distributed in female fertile rings; this result indicates that protoperithecia occur only in mycelial areas that have a restricted range of age at the time that modA modB thalli complete growth. Furthermore, nonsense mutations of incompatibility genes suppress the modA modB female fertile rings or restrict their width, suggesting that incompatibility loci, like the mod loci, are involved in protoperithecium formation. Taken together, these results lead to the postulate that mod and incompatibility genes do not determine, sensu stricto, protoperithecial function, as previously supposed (Boucherie and Bernet 1974), but may be involved in the homeostatic control of stationary cell functions essential for the complete development of the female sexual cycle.
Insights
Mutations in modA and modB genes cause female sterility, revealing these genes are crucial for sexual cycle development beyond protoplasmic incompatibility. These genes regulate cell functions essential for protoperithecia formation and ascospore maturation.
Area of Science:
- Genetics
- Mycology
- Developmental Biology
Background:
- Protoplasmic incompatibility in fungi is regulated by nonallelic gene interactions, specifically involving modA and modB genes.
- modA modB mutant strains exhibit female sterility, offering a unique model to study gene functions beyond incompatibility.
Purpose of the Study:
- To investigate the role of modA and modB genes in fungal sexual development.
- To determine if mod and incompatibility loci are involved in functions beyond protoplasmic incompatibility.
- To elucidate the developmental timing and genetic control of protoperithecia formation.
Main Methods:
- Utilizing modA modB mutant strains exhibiting temperature-dependent female sterility.
- Creating heterokaryotic mycelia combining modA modB nuclei with wild-type or single mutant nuclei.
- Supplementing culture media with specific amino acids.
- Analyzing the distribution and formation of protoperithecia in various mutant backgrounds.
- Introducing nonsense mutations in incompatibility genes.
Main Results:
- modA modB female sterility is a nonautonomous trait, with heterokaryons restoring fertility and protoperithecia formation.
- Protoperithecia formation is observed on specific amino acid-supplemented media.
- mod mutations do not exhibit specific sequential timing, affecting the sexual cycle at various developmental stages.
- Protoperithecia in modA modB cultures form in fertile rings, indicating age-restricted formation.
- Incompatibility gene mutations affect modA modB female fertile rings, suggesting a role in protoperithecia development.
Conclusions:
- mod and incompatibility genes are essential for the homeostatic control of stationary cell functions required for complete female sexual cycle development.
- These genes are not solely responsible for protoperithecial function but regulate underlying cellular processes.
- The findings challenge previous assumptions about the direct role of these genes in protoperithecia formation.
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