Characterization of the mating-type locus in Diplodia species.

Bazerbachi, A.*, Slippers, B., Duong, T. A., Barnes, I., Wingfield, M. J., Wingfield, B. D.

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

The genus Diplodia comprises several phytopathogenic fungi known to cause disease on numerous economically significant plants, including angiosperm and gymnosperm tree species. Notable species such as Diplodia sapinea, D. scrobiculata, D. seriata, D. mutila, D. intermedia, and D. corticola are associated with tip blight, cankers, and dieback symptoms, often leading to substantial losses in forestry and agriculture. Despite their importance, little is known regarding the reproductive biology of many Diplodia species, particularly the genetic basis of their mating systems. Using whole genome sequences, the mating-type (MAT) loci in these species were characterized. This involved analysing their genomes and leveraging the known MAT idiomorph sequences of D. sapinea to characterize and compare the MAT loci across all six species. Results showed that the organization of the MAT locus and flanking genes is relatively conserved in most cases, with the exception of D. mutila where notable differences in synteny were observed. All species manifested a typical heterothallic mating system, characterized by the presence of either a MAT1-1 or MAT1-2 idiomorph in a single isolate. The MAT1-1 idiomorph was defined by the MAT1-1-1 gene, which encodes a transcriptional regulatory protein with a highly conserved α-box domain. Similarly, the MAT1-2 idiomorph was defined by the MAT1-2-1 gene, encoding a protein with an HMG-box domain. In addition to the MAT1-1-8 gene and the MAT1-2-5 gene present in the MAT1-1 and MAT1-2 idiomorphs respectively, the same five open reading frames (ORFs) were found located between the MAT locus and the DNA lyase gene on the 5’ end of each idiomorph. These ORFs include Cytochrome c oxidase subunit VIa (Cox-Via), Anaphase-promoting complex subunit 5 (APC5), Complex I intermediate-associated protein 30 (CIA30), Mitochondrial carrier protein (MCP), and Phosphoribosylaminoimidazolesuccinocarbox-amide Synthetase (SAICARsyn). Understanding the genetic basis of mating systems in these fungi enhances the knowledge of their population biology and potential for recombination.

Keywords: Diplodia, phytopathogenic fungi, mating-type loci, MAT idiomorphs, synteny