During the sexual phase of Neurospora crassa, unpaired genes are subject to a silencing mechanism known as meiotic silencing by unpaired DNA (MSUD). MSUD targets the transcripts of an unpaired gene and utilizes typical RNA interference factors for its process. Using a reverse genetic screen, we have identified a meiotic silencing gene called sad-9, which encodes a DEAD-box RNA helicase. While not essential for vegetative growth, SAD-9 plays a crucial role in both sexual development and MSUD. Our results suggest that SAD-9, with the help of the SAD-2 scaffold protein, recruits the SMS-2 Argonaute to the perinuclear region, the center of MSUD activity.
An NCBP3-Domain Protein Mediates Meiotic Silencing by Unpaired DNA
Abstract In the filamentous fungus Neurospora crassa, genes unpaired during meiosis are silenced by a process known as meiotic silencing by unpaired DNA (MSUD). MSUD utilizes common RNA interference (RNAi) proteins, such as Dicer and Argonaute, to target homologous mRNAs for silencing. Previously, we demonstrated that nuclear cap-binding proteins NCBP1 and NCBP2 are involved in MSUD. We report here that SAD-8, a protein similar to human NCBP3, also mediates silencing. Although SAD-8 is not essential for either vegetative or sexual development, it is required for MSUD. SAD-8 localizes predominantly in the nucleus and interacts with both NCBP1 and NCBP2. Similar to NCBP1 and NCBP2, SAD-8 interacts with a component (Argonaute) of the perinuclear meiotic silencing complex (MSC), further implicating the involvement of cap-binding proteins in silencing.
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- Award ID(s):
- 1715534
- NSF-PAR ID:
- 10223536
- Date Published:
- Journal Name:
- G3 Genes|Genomes|Genetics
- Volume:
- 10
- Issue:
- 6
- ISSN:
- 2160-1836
- Page Range / eLocation ID:
- 1919 to 1927
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Abstract In Neurospora crassa, expression from an unpaired gene is suppressed by a mechanism known as meiotic silencing by unpaired DNA (MSUD). MSUD utilizes common RNA interference (RNAi) factors to silence target mRNAs. Here, we report that Neurospora CAR-1 and CGH-1, homologs of two Caenorhabditis elegans RNA granule components, are involved in MSUD. These fungal proteins are found in the perinuclear region and P-bodies, much like their worm counterparts. They interact with components of the meiotic silencing complex (MSC), including the SMS-2 Argonaute. This is the first time MSUD has been linked to RNA granule proteins.more » « less
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Meiotic silencing by unpaired DNA (MSUD) is a gene silencing process that occurs within meiotic cells of Neurospora crassa and other fungi. We have previously developed a high-throughput screen to identify suppressors of this silencing pathway. Here, a list of MSUD suppressor candidates from a single pass of the first 84 plates of the Neurospora knockout library is provided.more » « less
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null (Ed.)Meiotic drive elements cause their own preferential transmission following meiosis. In fungi, this phenomenon takes the shape of spore killing, and in the filamentous ascomycete Neurospora sitophila , the Sk-1 spore killer element is found in many natural populations. In this study, we identify the gene responsible for spore killing in Sk-1 by generating both long- and short-read genomic data and by using these data to perform a genome-wide association test. We name this gene Spk-1 . Through molecular dissection, we show that a single 405-nt-long open reading frame generates a product that both acts as a poison capable of killing sibling spores and as an antidote that rescues spores that produce it. By phylogenetic analysis, we demonstrate that the gene has likely been introgressed from the closely related species Neurospora hispaniola , and we identify three subclades of N. sitophila , one where Sk-1 is fixed, another where Sk-1 is absent, and a third where both killer and sensitive strain are found. Finally, we show that spore killing can be suppressed through an RNA interference-based genome defense pathway known as meiotic silencing by unpaired DNA. Spk-1 is not related to other known meiotic drive genes, and similar sequences are only found within Neurospora . These results shed light on the diversity of genes capable of causing meiotic drive, their origin and evolution, and their interaction with the host genome.more » « less
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Summary Ascospores are the primary inoculum in
Fusarium graminearum . Interestingly, 70 of its genes have premature stop codons (PSC) and require A‐to‐I editing during sexual reproduction to encode full‐length proteins, including the ortholog of yeast Ama1, a meiosis‐specific activator of APC/C. In this study, we characterized the function ofFgAMA1 and its PSC editing.FgAMA1 was specifically expressed during sexual reproduction. TheFgama1 mutant was normal in growth and perithecium formation but defective in ascospogenesis. Instead of forming four‐celled, uninucleate ascospores,Fgama1 mutant produced oval, single‐celled, binucleated ascospores by selfing. Some mutant ascospores began to bud and underwent additional mitosis inside asci. Expression of the wild‐type or editedFgAMA1 but not the uneditable allele complementedFgama1 . In theFgama1 xmat‐1‐1 outcross, over 60% of the asci had eightFgama1 or intermediate (elongated but single‐celled) ascospores, suggesting efficient meiotic silencing of unpairedFgAMA1 . Deletion ofFgPAL1 , one of the genes upregulated inFgama1 also resulted in defects in ascospore morphology and budding. Overall, our results showed thatFgAMA1 is dispensable for meiosis but important for ascospore formation and discharge. InF. graminearum , whereas some of its targets are functional during meiosis, FgAma1 may target other proteins that function after spore delimitation.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1534/g3.120.401236
