Two genomes are better than one: history, genetics, and biotechnological applications of fungal heterokaryons

Abstract

Heterokaryosis is an integral part of the parasexual cycle used by predominantly asexual fungi to introduce and maintain genetic variation in populations. Research into fungal heterokaryons began in 1912 and continues to the present day. Heterokaryosis may play a role in the ability of fungi to respond to their environment, including the adaptation of arbuscular mycorrhizal fungi to different plant hosts. The parasexual cycle has enabled advances in fungal genetics, including gene mapping and tests of complementation, dominance, and vegetative compatibility in predominantly asexual fungi. Knowledge of vegetative compatibility groups has facilitated population genetic studies and enabled the design of innovative methods of biocontrol. The vegetative incompatibility response has the potential to be used as a model system to study biological aspects of some human diseases, including neurodegenerative diseases and cancer. By combining distinct traits through the formation of artificial heterokaryons, fungal strains with superior properties for antibiotic and enzyme production, fermentation, biocontrol, and bioremediation have been produced. Future biotechnological applications may include site-specific biocontrol or bioremediation and the production of novel pharmaceuticals.

The plasticity of fungal interactions

“…The hypha, with its unusual type of cell organization unknown among other living organisms, belongs to the former group, while among the latter, in fungi it is difficult to define an individual, which is a highly important character when comparing fungi and macroeukaryotes. Also, fungi are capable of performing anastomosis, the fusion of encountering vegetative hyphae, resulting in heterokaryosis, i.e., the advantage of having two genomes instead of a single one (Chagnon 2014;Strom and Bushley 2016). Furthermore, fungal reproduction is quite unusual.…”

Limitation of nitrogen source facilitated the production of nonmeiotic recombinants in Aspergillus nidulans

“…This response was considered adaptive by the authors, permitting fungal survival when assimilating nitrogen was absent from the external environment . As genetic exchanges between compatible fungal strains cause them to update their genomes , in our analysis, the limited access to nitrogen in BM may have stimulated the fusion of parental nuclei inside the heterokaryon as a survival strategy and facilitated the emergence of new recombinant genotypes, more adapted to the limited nutrient availability. As previously observed in A. niger and C. sublineolum , the nonmeiotic recombinants obtained in our assay have probably originated from highly unstable diploid nuclei that, posterior to mitotic recombination, rapidly returned to the haploid condition, still in the heterokaryotic hyphal stage, and before conidia formation .…”

“…Parasexual recombinants, produced in the parasexual cycle, resulting from the haploidization of diploid nuclei, which may be isolated and maintained indefinitely in the appropriate culture media . On the contrary, nonmeiotic recombinants were obtained in the current study only by the parameiotic process, which does not allow the recovery of the diploid phase (Table S4).…”

Intergeneric fusant development using chitinase preparation of Rhizopus stolonifer NCIM 880

“…Likewise, Patil et al (2015) reported intergeneric fusion between A. oryzae and T. harzianum . Strom and Bushley (2016) described role of heterokaryotic fungi with distinct traits for antibiotic and enzyme production, fermentation, biocontrol, and bioremediation.…”