Enabling breeding with the highly specific lignin-degrading white-rot fungus Gelatoporia subvermispora

White rot fungi can be used to upgrade lignocellulosic side streams for biorefinery, bioenergy and ruminant feed. However, to make such pretreatments economically feasible, the efficiency, both in terms of specificity and required processing time, must be further optimized. In addition to technical advancements, breeding fungal species offers a promising approach to improving the fungal pretreatment of lignocellulose. Gelatoporia subvermispora is recognized as one of the most selective lignin degraders. This study aimed to establish the prerequisites for breeding this species by reproducing its life cycle on a laboratory scale, characterizing its mating system, genotyping haplotypes from a wild strain collection, and assessing the mating compatibility of these haplotypes.

The constituent monokaryons of ten wild G. subvermispora strains (USA and Canadian origin) were recovered via protoplasting mycelial cultures. All monokaryons were resequenced and alignment to a de novo generated reference genome revealed a high genetic diversity. The monokaryons from both the same and different geographic regions were found to be mating compatible. Newly generated dikaryons and original wild isolates could be fruited on malt extract agar and on organic substrates. Fruitbodies generated basidiospores that could be germinated on Petri dishes. Mating experiments using a half-diallel matrix demonstrated a tetrapolar mating system. Resequencing data further elucidated the structure of the mating loci, revealing: (i) a Homeodomain locus with two outward-oriented homeodomain genes, and (ii) a Pheromone Receptor locus comprising three or four STE pheromone receptor genes and two conserved STE pheromone receptor-like genes, the latter conserved in all strains.

This study demonstrates the extensive genetic diversity within wild G. subvermispora populations and the broad compatibility between strains. Successfully reproducing the complete life cycle under laboratory conditions, combined with previously observed phenotypic variation, highlights this species as an excellent candidate for breeding programs aimed at improving lignocellulosic side stream valorisation. To date, fungal breeding for such traits has not been explored, making this research a significant step toward optimizing fungal bioconversion processes.