Studies on the biological significance of RNA editing in filamentous fungi

RNA editing is the selective insertion, deletion, or substitution of nucleotides and is conserved in all domains of life. RNA editing of protein-coding transcripts leads to sequence changes in the transcript as well as the protein that could alternatively be directly encoded in the DNA. In filamentous ascomycetes, adenosine (A) to inosine (I) RNA editing was recently detected to occur in protein-coding transcripts during sexual reproduction. It is supposed to be generally adaptive and has been hypothesized to be required for ascospore formation and / or ascospore germination. However, many open questions about fungal editing remain.

To gain insight into the biological role of editing, we analyzed genes whose transcripts are affected by editing in the ascomycete Sordaria macrospora. Deletion of several efd genes indeed revealed a function of these genes during ascospore formation and/or discharge. Complementation studies with mutations of the native stop codon to a TGG (always long protein) or a TAA (always short protein) revealed possible functions for the editing sites in ascospore formation. Studies on the function of editing during ascospore germination in different physiological conditions are underway. Further, we study mutants unable to form ascospores for the detection of editing regulators. Taken together, these studies should provide insight into ascospore formation in fungi, but also into the widespread phenomenon of mRNA editing also found in metazoans and bacteria.