The MAT1 locus in Cryphonectria species.

Selebi, A. P.*, Pham, N., Wingfield, B. D.

Forestry and Agricultural Biotechnology Institute, Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria, South Africa

The genus Cryphonectria is the best studied in the family Cryphonectriaceae. There are ten species currently recognised in this genus. While most are considered to be saprobes, the genus also includes some important pathogens. Cryphonectria parasitica has nearly irradicated the American chestnut and has severely impacted chestnut trees in Europe. Genetic diversity and mating strategies play a large role in the success of pathogenic fungi. The MAT1 locus determines the mating strategy of heterothallic fungi and has been studied in C. parasitica. However, there is still ambiguity around the mating strategy of other Cryphonectria species. This study aimed to characterise and compare the MAT1 locus of the species for which genome sequence data is available. These are C. macrospora, C. parasitica, C. radicalis, C. carpinicola, C. decipiens and C. japonica. The MAT1 locus was extracted from the genomes of these fungi and the annotation program Augustus was used to determine the putative genes present in and around the MAT1 locus. Where available RNA sequencing data was used to verify the annotation and expression of these genes. A second, previously uncharacterized, gene was found in the MAT1-2 idiomorph. The gene, putatively described as MAT1-2-16, was present in all the species studied. Cryphonectria macrospora and C. japonica isolates have both MAT1-1 and MAT1-2 genes in the MAT1 locus suggesting that they are homothallic. Cryphonectria parasitica, C. carpinicola, and C. radicalis have MAT1 loci typical of heterothallic fungi. However, some C. parasitica and C. radicalis isolates appear dikaryotic. The discovery of the MAT1-2-16 gene across all studied species, along with the evidence of homothallic and heterothallic characteristics within the genus, highlights the complex and varied mating strategies of Cryphonectria species and underscores the need for further research to fully understand their reproductive biology.

Keywords: Cryphonectria, Cryphonectria parasitica, Mating system, Plant Pathology, MAT1