Pervasive transcription of the mitochondrial genome in <i>Candida albicans</i> is revealed in mutants lacking the mtEXO RNase complex
Karolina Łabędzka-Dmoch, Adam Kolondra, Magdalena A. Karpińska, Sonia Dębek, Joanna Grochowska, Maciej Grochowski, Jakub Piątkowski, Thi Hoang Diu Bui, Paweł Golik
Abstract
gene results in multiple defects in mitochondrial genome expression leading to the loss of respiratory competence. Transcriptomic analysis reveals pervasive transcription in mutants lacking the mtEXO activity, with evidence of the entire genome being transcribed, whereas in wild-type strains no RNAs corresponding to a significant fraction of the noncoding genome can be detected. Antisense ('mirror') transcripts, absent from normal mitochondria are also prominent in the mutants. The expression of multiple mature transcripts, particularly those translated from bicistronic mRNAs, as well as those that contain introns is affected in the mutants, resulting in a decreased level of proteins and reduced respiratory complex activity. The phenotype is most severe in the case of Complex IV, where a decrease of mature COX1 mRNA level to ~5% results in a complete loss of activity. These results show that RNA degradation by mtEXO is essential for shaping the mitochondrial transcriptome and is required to maintain the functional demarcation between transcription units and non-coding genome segments.