The MAT1-1-1 and MAT1-2-1 genes are thought to be the master regulators
of sexual development in most ascomycete fungi, and they are often essential for
this process. In contrast, it has been suggested that the secondary mating-type genes
act to calibrate the sexual cycle and can be dispensable. Recent functional characterization
of genes such as Aspergillus fumigatus MAT1-2-4, Huntiella omanensis MAT1-2-7,
and Botrytis cinerea MAT1-1-5 has, however, shown that these secondary genes may
play more central roles in the sexual pathway and are essential for the production of
mature fruiting structures. We used a comparative transcriptome sequencing (RNAseq)
experiment to show that the truncation of MAT1-2-7 in the wood inhabiting H.
omanensis residing in the Ceratocystidaceae is associated with the differential expression
of approximately 25% of all the genes present in the genome, including the
transcriptional regulators ste12, wc-2, sub1, VeA, HMG8, and pro1. This suggests that
MAT1-2-7 may act as a transcription factor and that DMAT1-2-7 mutant sterility is the
result of layered deregulation of a variety of signaling and developmental pathways.
This study is one of only a few that details the functional characterization of a secondary
MAT gene in a nonmodel species. Given that this gene is present in other
Ceratocystidaceae species and that there are diverse secondary MAT genes present
throughout the Pezizomycotina, further investigation into this gene and others like it
will provide a clearer understanding of sexual development in these eukaryotes.
IMPORTANCE Secondary mating-type genes are being described almost as quickly as
new fungal genomes are being sequenced. Understanding the functions of these genes
has lagged behind their description, in part due to limited taxonomic distribution, lack of conserved functional domains, and difficulties with regard to genetic manipulation protocols.
This study aimed to address this by investigating a novel mating-type gene, MAT1-
2-7, for which two independent mutant strains were generated in a previous study. We
characterized the molecular response to the truncation of this gene in a nonmodel,
wood-infecting fungus and showed that it resulted in widespread differential expression
throughout the transcriptome of this fungus. This suggests that secondary MAT genes
may play a more important role than previously thought. This study also emphasizes the
need for further research into the life cycles of nonmodel fungi, which often exhibit
unique features that are very different from the systems understood from model species.