Abstract
Over the last one and a half decade, interspecies hybridisation has gained continuously increasing attention as a breeding technique suitable for transferring of genetic information between Saccharomyces species and mixing of their gene pools without genetic engineering. The hybrids frequently show positive transgressive phenotypes. Segregation of the hybrid genome results in mosaic (chimeric) strains that can outperform both the parents and the hybrids or exhibit novel positive phenotypic properties. Mitotic segregation can take place during the vegetative propagation of the sterile allodiploid hybrid cells. Meiotic segregation becomes possible after genome duplication (tetraploidisation) if it is followed by break-down of sterility. The allotetraploid cells are seemingly fertile because they form viable spores. But because of the autodiploidisation of the meiosis, sterile allodiploid spores are produced and thus the hybrid genome does not segregate (the second sterility barrier). However, malsegregation of MAT-carrying chromosomes in one of the subgenomes during allotetraploid meiosis (loss of MAT heterozygosity) results in fertile alloaneuploid spores. The breakdown of (the second) sterility barrier is followed by the loss of additional chromosomes in rapid succession and recombination between the subgenomes. The process (genome autoreduction in meiosis or GARMe) chimerises the genome and generates strains with chimeric (mosaic) genomes composed of various combinations of the genes of the parental strains. Since one of the subgenomes is preferentially reduced, the outcome is usually a strain having an (almost) complete genome from one parent and only a few genes or mosaics from the genome of the other parent. The fertility of the spores produced during GARMe provides possibilities also for introgressive backcrossing with one or the other parental strain, but genome chimerisation and gene transfer through series of backcrosses always with the same parent is likely to be less efficient than through meiotic or mitotic genome autoreduction. Hybridisation and the evolution of the hybrid genome (resizing and chimerisation) have been exploited in the improvement of industrial strains and applied to the breeding of new strains for specific purposes. Lists of successful projects are shown and certain major trends are discussed.
Highlights
Strains of Saccharomyces cerevisiae, the major yeast used in fermentation technologies (Tuite and Oliver, 1991) show high genetic and phenotypic diversity
GARMe (Genome Autoreduction in Meiosis) generates chimeric genomes in series of successive meiotic divisions after the breakdown of the sterility barrier upon tetraploidisation (Karanyicz et al, 2017), whereas GARMi (Genome Autoreduction in Mitosis) is its counterpart operating during vegetative propagation of the hybrid cells
Numerous early studies have shown that the sterility of the hybrids of different plant and animal species is due to inadequate or deficient chromosome pairing during meiosis (e.g., Walters, 1958; John and Weissman, 1977; Gangadevi et al, 1985)
Summary
Segregation of the hybrid genome results in mosaic (chimeric) strains that can outperform both the parents and the hybrids or exhibit novel positive phenotypic properties. Because of the autodiploidisation of the meiosis, sterile allodiploid spores are produced and the hybrid genome does not segregate (the second sterility barrier). The process (genome autoreduction in meiosis or GARMe) chimerises the genome and generates strains with chimeric (mosaic) genomes composed of various combinations of the genes of the parental strains. The fertility of the spores produced during GARMe provides possibilities for introgressive backcrossing with one or the other parental strain, but genome chimerisation and gene transfer through series of backcrosses always with the same parent is likely to be less efficient than through meiotic or mitotic genome autoreduction.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have