Comparative Analysis of Lifecycle-Dependent A to I RNA Editing in Three Members of the Microbotryum violaceum Fungal Complex

A-to-I RNA editing is increasingly recognized as a regulator of fungal development and pathogenesis, yet its extent and lifecycle dependence remain poorly characterized in basidiomycetes. Microbotryum superbum (MvSup), M. intermedium (MI), and M. lychnidis-dioicae (MVLG) are members of the M. violaceum fungal complex. Each species infects specific host plant species, resulting in commonly anther-smut disease. The lifecycle of these basidiomycete fungi includes the haploid, mating, and infection stages. RNA editing is a post-transcriptional process where adenosine (A) is converted to inosine (I) by adenosine deaminase enzymes, and such modifications to RNAs may lead to synonymous and nonsynonymous codon changes, thereby altering protein function. Here, we compared A-to-I editing across the haploid, mating, and infection stages of these three related species to determine how editing patterns vary with lifecycle stage and among closely related fungal pathogens. The a2 haploid strain of MI had fewer editing sites compared to other haploid strains. The predicted codon/amino acid changes in each haploid strain across the three species indicated three primary types of resulting amino acid substitutions that were common to both of the mating-type strains across the three species: threonine to alanine, lysine to glutamic acid, and valine to alanine. During the mating stage of MvSup, a synonymous codon change was found in a mitogen-activated protein kinase domain-containing protein within the protein’s conserved region. Gene expression analysis revealed that certain genes, uniquely edited during the mating stage of MvSup, tend to be upregulated in the haploid stage but downregulated during mating, and vice versa. Research on RNA editing in basidiomycetes is relatively new. RNA editing mechanisms in fungi have been implicated in fungal pathogenesis, although the exact roles and implications remain unclear. Additional research will help us understand the functional significance of this apparently ubiquitous process in several members of the Microbotryum fungal complex, with possible ramifications more generally in fungi.