Genetic Dissection of Sexual Reproduction in a Primary Homothallic Basidiomycete

Author: mycolabadmin
2016-06-21
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Summary

This research investigated how a particular yeast species can reproduce sexually without requiring a mating partner, unlike most other related fungi. The scientists identified and studied the genes responsible for this self-fertile reproduction system, which could have important applications in biotechnology. The yeast studied, Phaffia rhodozyma, is commercially important because it produces astaxanthin, a valuable antioxidant pigment used in food and cosmetics industries. Impacts on everyday life: • Improved understanding of this yeast’s reproduction could lead to better industrial strains for astaxanthin production • Advances our knowledge of how organisms can adapt different reproductive strategies • Could help develop new approaches for improving production of natural food colorants and antioxidants • Demonstrates how basic research on microorganisms can have practical applications in food and cosmetic industries • Provides tools for creating better yeast strains through classical breeding approaches

Background

In fungi belonging to the phylum Basidiomycota, sexual compatibility is usually determined by two genetically unlinked MAT loci – one encoding pheromone receptors and pheromone precursors, and another encoding homeodomain transcription factors. Most species are heterothallic, requiring mating between sexually compatible individuals with different MAT alleles. However, some species are homothallic, capable of completing the sexual cycle without mating with genetically distinct partners. While heterothallic life cycles have been well studied in basidiomycete model species, much less is known about the molecular basis for homothallism.

Objective

To determine the role of pheromone receptor (P/R) and homeodomain (HD) genes in sexual development of the homothallic basidiomycetous yeast Phaffia rhodozyma through genetic analysis using available molecular tools.

Results

Two P/R clusters were found, each containing one pheromone receptor and one pheromone precursor gene, forming two redundant P/R pairs. Each receptor was activated by the pheromone encoded by the most distal pheromone precursor gene. The HD locus encoded a single pair of divergently transcribed HD1 and HD2 transcription factors, both required for normal completion of the sexual cycle. The researchers successfully generated artificial heterothallic strains through strategic gene deletions.

Conclusion

P. rhodozyma appears to be a primarily homothallic organism with MAT genes that likely evolved from a heterothallic ancestor. Both P/R and HD systems are functional and required for sexual development. The HD proteins may interact weakly to regulate sexual development genes. This work provides the first detailed mechanistic model for primary homothallism in a basidiomycete and enables new approaches for strain improvement through controlled outcrossing.

Published in:PLOS Genetics,
Study Type:Genetic Analysis,
Source: 10.1371/journal.pgen.1006110