Sculpting fungal fate: the importance of RNA editing for developmental morphogenesis in filamentous fungi

RNA editing, the post-transcriptional selective insertion, substitution or deletion of nucleotides plays a crucial role in functional diversity of gene expression within all domains of life. In ascomycetes, a diverse group of filamentous fungi RNA editing primarily involves adenosine-to-inosine (A-to-I) conversions. In contrast to animals the A-to-I editing occur predominantly within coding regions of transcripts involved in sexual reproduction. Interestingly, not only amino acid codons but also stop codons tend to be affected by editing leading to a change of TAG or TGA codons to TGG tryptophan codons. The precise mechanisms regulating the conversion of the codons still need further investigation. However, A-to-I RNA editing is suggested to play a crucial role in the formation of sexual structures like ascospores and fruiting bodies and might also provide proteome diversity that benefits the progeny.

To unravel the biological importance of A-to-I editing during development morphogenesis in filamentous fungi we analyzed so called efd (edited in fruiting body development) genes in the ascomycete Sordaria macrospora. Intriguingly, several deletion mutants of efd genes like efd4 and efd7 showed severe defects in their ascospore formation and/or discharge. Interestingly, complementation studies with constructs expressing either the edited version (TGG) or non-edited version (TAA) revealed putative functions for the editing sites during reproduction. Very recent results suggest a role for efd16 in cellular structure and physical properties of sexual reproduction structures. To investigate this further we are applying a novel method measuring structural integrity of ascospores. These data will provide better insight of the impact of A-to-I editing during developmental processes and its role for the adaptive capabilities and morphogenesis of fungi.