UC Riverside

Sexual reproduction and sexual development in fungi is coordinated by single, differentially encoded genes. The Mucoromycotina are a subphylum of the Mucoromycota, a group that is sister to the dikaryan lineages. Mucoromycetes are capable of asexual and sexual reproduction. Sexual reproduction in this lineage is coordinated by a single HMG-domain gene at the mating-type locus. The sexual cycle of Phycomyces blakesleeanus involves well characterized cell differentiation events, but less is known the genetic mechanisms underlying these morphological transitions. Time series trancsriptomes were generated for three timepoints during the P. blakesleeanus sexual cycle. The differentially expressed genes were correlated with the development of specific sexual structures. In a recapitulation of prior studies, the mating-type genes and carotenoid biosynthetic genes were also differentially expressed. Coexpression clusters were identified and they also correlated with a particular stage during sexual development. Many of the differentially co-expressed genes that were identified are conserved in other fungal species and also play roles in sexual development, suggesting the existence of sexual developmental toolkits. Additionally, phenotypic differences between the two mating-types of P. blakesleeanus were observed. The vegetative transcriptomes of each mating-type were characterized and evidence was found for mating-type-biased gene expression. Mating-type biased gene expression points to a role for the mating-type genes during vegetative growth. Lastly, the evolution of mating-type loci across the subphylum mucoromycota was explored. A high-throughput strategy for identifying these loci was developed and the resulting analysis identified mating-types in 427 isolates. Support was found for a stepwise assembly of mating-type locus genes akin to the stepwise evolution of sex chromsomes. Furthermore, assessment of the evolution of the individual mating-type genes suggested that SexP may have evolved before SexM and that SexM evolved from SexP.