A non-canonical RNA degradation pathway suppresses RNAi-dependent epimutations in the human fungal pathogen Mucor circinelloides.
Mucorales are a group of basal fungi that includes the casual agents of the human emerging disease mucormycosis. Recent studies revealed that these pathogens activate an RNAi-based pathway to rapidly generate drug-resistant epimutant strains when exposed to stressful compounds such as the antifungal drug FK506. To elucidate the molecular mechanism of this epimutation pathway, we performed a genetic analysis in Mucor circinelloides that revealed an inhibitory role for the non-canonical RdRP-dependent Dicer-independent silencing pathway, which is an RNAi-based mechanism involved in mRNA degradation that was recently identified. Thus, mutations that specifically block the mRNA degradation pathway, such as those in the genes r3b2 and rdrp3, enhance the production of drug resistant epimutants, similar to the phenotype previously described for mutation of the gene rdrp1. Our genetic analysis also revealed two new specific components of the epimutation pathway related to the quelling induced protein (qip) and a Sad-3-like helicase (rnhA), as mutations in these genes prevented formation of drug-resistant epimutants. Remarkably, drug-resistant epimutant production was notably increased in M. circinelloides f. circinelloides isolates from humans or other animal hosts. The host-pathogen interaction could be a stressful environment in which the phenotypic plasticity provided by the epimutant pathway might provide an advantage for these strains. These results evoke a model whereby balanced regulation of two different RNAi pathways is determined by the activation of the RNAi-dependent epimutant pathway under stress conditions, or its repression when the regular maintenance of the mRNA degradation pathway operates under non-stress conditions.
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.
Silvia
0000-0003-3014-7372
S
Calo
Department of Genetics and Microbiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Francisco E
0000-0003-3762-5971
FE
Nicolás
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.
Soo Chan
SC
Lee
Department of Genetics and Microbiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Ana
0000-0002-0445-4400
A
Vila
Department of Genetics and Microbiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Maria
0000-0001-5661-9441
M
Cervantes
Department of Genetics and Microbiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Santiago
S
Torres-Martinez
Department of Genetics and Microbiology, Faculty of Biology, University of Murcia, Murcia, Spain.
Rosa M
0000-0002-6675-8506
RM
Ruiz-Vazquez
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.
Maria E
ME
Cardenas
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America.
Joseph
0000-0001-6369-5995
J
Heitman
D000595:Amino Acid Sequence; D025141:Drug Resistance, Fungal / Q000187:drug effects / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D054884:Host-Pathogen Interactions; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008957:Models, Genetic; D009089:Mucor / Q000235:genetics*; D009091:Mucormycosis / Q000382:microbiology; D009154:Mutation; D034622:RNA Interference; D020871:RNA Stability; D012331:RNA, Fungal / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D016559:Tacrolimus / Q000494:pharmacology
D005656:Fungal Proteins; D007166:Immunosuppressive Agents; D012331:RNA, Fungal; D012333:RNA, Messenger; D016559:Tacrolimus