Efficient gene editing in Neurospora crassa with CRISPR technology
© Matsu-ura et al. 2015
Received: 15 April 2015
Accepted: 2 July 2015
Published: 15 July 2015
Efficient gene editing is a critical tool for investigating molecular mechanisms of cellular processes and engineering organisms for numerous purposes ranging from biotechnology to medicine. Recently developed RNA-guided CRISPR/Cas9 technology has been used for efficient gene editing in various organisms, but has not been tested in a model filamentous fungus, Neurospora crassa.
In this report, we demonstrate efficient gene replacement in a model filamentous fungus, Neurospora crassa, with the CRISPR/Cas9 system. We utilize Cas9 endonuclease and single crRNA:tracrRNA chimeric guide RNA (gRNA) to: (1) replace the endogenous promoter of clr-2 with the β-tubulin promoter, and (2) introduce a codon optimized fire fly luciferase under the control of the gsy-1 promoter at the csr-1 locus. CLR-2 is one of the core transcription factors that regulate the expression of cellulases, and GSY-1 regulates the conversion of glucose into glycogen. We show that the β-tubulin promoter driven clr-2 strain shows increased expression of cellulases, and gsy-1-luciferase reporter strain can be easily screened with a bioluminescence assay.
CRISPR/Cas9 system works efficiently in Neurospora crassa, which may be adapted to Neurospora natural isolates and other filamentous fungi. It will be beneficial for the filamentous fungal research community to take advantage of CRISPR/Cas9 tool kits that enable genetic perturbations including gene replacement and insertions.
KeywordsNeurospora crassa CRISPR/Cas9 Genome editing Homologous recombination Biofuel Cellulase
Genetic engineering of organisms of interest are critical tools to elucidate molecular and cellular processes or to engineer organisms with new characteristics or traits. Clustered regularly interspaced short palindromic repeats (CRISPR)-associated RNA-guided DNA endonuclease, Cas9, has been driving the latest gene editing technology by taking advantage of the simple design of a single crRNA:tracrRNA chimeric guide RNA (gRNA). gRNA includes 20 base pairs of target sequences that causes double strand breaks by Cas9 at the target locus, which triggers gene replacement by homologous recombination (HR) [1–3] (reviewed by Hsu et al. ). CRISPR/Cas9 system has been utilized for gene editing ranging from yeast to human cells including filamentous fungi [5–8].
A model filamentous fungus, Neurospora crassa, has been used to elucidate fundamental molecular mechanisms including the one gene-one enzyme hypothesis, cell fusion, circadian rhythms, and epigenetics among others . Gene editing by HR was a difficult task in N. crassa until the discovery of highly efficient gene replacement in Neurospora strains lacking mus-51 (NCU08290) or mus-52 (NCU00077), which are deficient in non-homologous end-joining . This finding facilitated the high-throughput generation of single gene deletion knockout (KO) collection of N. crassa . However, one has to backcross Neurospora transformants to wild type in order to eliminate mus-51 or mus-52 KO background, which may take anywhere between one to three months. More importantly, there are numerous Neurospora natural isolates that are difficult to generate initial mus-51 or mus-52 KO, which make gene editing difficult. Therefore, it is critical to establish an alternative gene editing technology for the Neurospora system.
Strains used in this study
FGSC# or reference
Wild type (WT)
Belden et al. 
As a proof of principle, we set out to test overexpression of cellulases with the β-tubulin promoter-driven expression of clr-2, and efficient selection of luciferase reporters with a bioluminescence assay. 5 μg of β-tubulin-clr-2 circular donor plasmids were transformed into wild type N. crassa (74-OR23-1 V A) along with different concentrations of Cas9 and gRNA circular plasmids (Figure 2b). Transformations were performed as previously described . Dose-dependent increase of the number of transformants of β-tubulin-clr-2 was obtained by addition of Cas9 and gRNA (Figure 2b; Cas9 and gRNA plasmids: 0 µg: 1.0 ± 0.6; 1 µg: 0.8 ± 0.5; 2.5 µg: 42.0 ± 29.7; 5 µg 141.8 ± 92.9; n = 3, p < 0.01; Tukey’s method). We utilized optimal concentrations (5 µg) of Cas9 and gRNA with gsy-1-luciferase::csr-1 donor plasmid to transform the ras-1 bd N. crassa strain  (Figure 2c). gsy-1-luciferase::csr-1 that targets csr-1 locus enables double selection for both Ignite® and cyclosporine A as previously described . As expected, we observed an efficient number of transformants of gsy-1-luciferase::csr-1 with optimized concentrations (Figure 2c; Cas9 and gRNA plasmids: 0 µg: 3.7 ± 1.9; 1 µg: 364.0 ± 33.1; n = 3, p < 0.01; Student’s t test). The transformants produced with the CRISPR/Cas9 system successfully express the transgene. The transformed conidia were plated onto luciferin containing plates, and in vivo luciferase activities were monitored with a charge-coupled device camera. We observed 57 luciferase positive colonies out of 1,092 total colonies with CRISPR/Cas9 system, but no positive colonies were observed with non-CRISPR/Cas9 method of transformation [11, 19] (Figure 2d–f). The reason for low number of positive colonies with bioluminescence assay is due to the small sizes of other colonies, which do not produce detectable signals.
Primers used in this study
Genomic PCR (Figure 3e)
qRT-PCR (Figure 4)
qRT-PCR (Figure 4)
qPCR (Figure 3b, e)
qRT-PCR (Figure 4a)
qRT-PCR (Figure 4b)
qRT-PCR (Figure 4b)
qPCR (Figure 3b, c)
qRT-PCR (Figure 4c)
qPCR (Figure 3c)
qRT-PCR (Figure 4d)
In this report, we successfully demonstrated efficient gene replacements utilizing CRISPR/Cas9 technology in a model filamentous fungus, N. crassa. N. crassa did not indicate any problems in expressing functional Cas9 endonuclease under the A. nidulans trpC promoter, and the SNR52 promoter is operational to express gRNA in N. crassa as in S. cerevisiae . These events enabled us to perform efficient knock-in of clr-2 with β-tubulin promoter and target gsy-1-luciferase bioluminescence reporter at the csr-1 locus with relatively simple modifications of template plasmids utilizing PCR and yeast recombination. In contrast to previously established gene editing protocols in Neurospora, CRISPR/Cas9 technology did not require mus-51 or mus-52 mutant backgrounds for efficient HR. This technology will enable efficient gene editing of any Neurospora natural isolates. Recent advancement and ramifications of CRISPR/Cas9 technology created numerous resources including multiplex gene replacements, transcriptional control, and inducible gene regulation . Implementation of this technology in fungal organisms will be highly beneficial for the fungal research community.
Materials and methods
clustered regularly interspaced short palindromic repeats
single crRNA:tracrRNA chimeric guide RNA
nuclear localization signal
- SNR52 :
small nucleolar RNA 52
protospacer adjacent motif
- gsy-1 :
polymerase chain reaction
quantitative polymerase chain reaction
quantitative reverse transcription polymerase chain reaction
standard error of the mean
number of experiments
TM designed the experiments. TM, MB, and JK performed experiments. CH and TM supervised the overall experiments and wrote the manuscript. All authors read and approved the final manuscript.
We thank Dr. George Church for donating p426-SNR52p-gRNA.CAN1.Y-SUP4t and p415-GalL-Cas9-CYC1t plasmids (Addgene plasmid #43803 and #43804) . This work was supported by the Department of Interior Grant D12AP00005.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- Jinek M, Chylinski K, Fonfara I, Hauer M, Doudna JA, Charpentier E (2012) A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity. Science 337(6096):816–821. doi:10.1126/science.1225829 PubMedView ArticleGoogle Scholar
- Cong L, Ran FA, Cox D, Lin S, Barretto R, Habib N et al (2013) Multiplex genome engineering using CRISPR/Cas systems. Science 339(6121):819–823. doi:10.1126/science.1231143 PubMed CentralPubMedView ArticleGoogle Scholar
- Mali P, Yang L, Esvelt KM, Aach J, Guell M, DiCarlo JE et al (2013) RNA-guided human genome engineering via Cas9. Science 339(6121):823–826. doi:10.1126/science.1232033 PubMed CentralPubMedView ArticleGoogle Scholar
- Hsu PD, Lander ES, Zhang F (2014) Development and applications of CRISPR-Cas9 for genome engineering. Cell 157(6):1262–1278. doi:10.1016/j.cell.2014.05.010 PubMed CentralPubMedView ArticleGoogle Scholar
- Sander JD, Joung JK (2014) CRISPR-Cas systems for editing, regulating and targeting genomes. Nat Biotechnol 32(4):347–355. doi:10.1038/nbt.2842 PubMed CentralPubMedView ArticleGoogle Scholar
- Vyas VK, Barrasa MI, Fink GR (2015) A CRISPR system permits genetic engineering of essential genes and gene families. Sci Adv 1(3):e1500248. doi:10.1126/sciadv.1500248 PubMed CentralPubMedView ArticleGoogle Scholar
- Liu R, Chen L, Jiang Y, Zhou Z, Zou G (2015) Efficient genome editing in filamentous fungus Trichoderma reesei using the CRISPR/Cas9 system. Cell Discov 1(15007)
- Noedvig CS, Nielsen JB, Mortensen UH (2015) A CRISPR/Cas9 system for genetic engineering of filamentous fungi. Fungal Genet Rep 60(Suppl):23Google Scholar
- Roche CM, Loros JJ, McCluskey K, Glass NL (2014) Neurospora crassa: looking back and looking forward at a model microbe. Am J Bot 101(12):2022–2035. doi:10.3732/ajb.1400377 PubMedView ArticleGoogle Scholar
- Ninomiya Y, Suzuki K, Ishii C, Inoue H (2004) Highly efficient gene replacements in Neurospora strains deficient for nonhomologous end-joining. Proc Natl Acad Sci USA 101(33):12248–12253. doi:10.1073/pnas.0402780101 PubMed CentralPubMedView ArticleGoogle Scholar
- Colot HV, Park G, Turner GE, Ringelberg C, Crew CM, Litvinkova L et al (2006) A high-throughput gene knockout procedure for Neurospora reveals functions for multiple transcription factors. Proc Natl Acad Sci USA 103(27):10352–10357. doi:10.1073/pnas.0601456103 PubMed CentralPubMedView ArticleGoogle Scholar
- Pall ML, Brunelli JP (1933) A series of six compact fungal transformation vectors containing polylinkers with multiple unique restriction sites. Fungal Genet Newsl 40:59–62Google Scholar
- Harismendy O, Gendrel CG, Soularue P, Gidrol X, Sentenac A, Werner M et al (2003) Genome-wide location of yeast RNA polymerase III transcription machinery. EMBO J 22(18):4738–4747. doi:10.1093/emboj/cdg466 PubMed CentralPubMedView ArticleGoogle Scholar
- DiCarlo JE, Norville JE, Mali P, Rios X, Aach J, Church GM (2013) Genome engineering in Saccharomyces cerevisiae using CRISPR-Cas systems. Nucleic Acids Res 41(7):4336–4343. doi:10.1093/nar/gkt135 PubMed CentralPubMedView ArticleGoogle Scholar
- Gooch VD, Mehra A, Larrondo LF, Fox J, Touroutoutoudis M, Loros JJ et al (2008) Fully codon-optimized luciferase uncovers novel temperature characteristics of the Neurospora clock. Eukaryot Cell 7(1):28–37. doi:10.1128/EC.00257-07 PubMed CentralPubMedView ArticleGoogle Scholar
- Coradetti ST, Craig JP, Xiong Y, Shock T, Tian C, Glass NL (2012) Conserved and essential transcription factors for cellulase gene expression in ascomycete fungi. Proc Natl Acad Sci USA 109(19):7397–7402. doi:10.1073/pnas.1200785109 PubMed CentralPubMedView ArticleGoogle Scholar
- de Paula R, de Azzariti Pinho C, Terenzi HF, Bertolini MC (2002) Molecular and biochemical characterization of the Neurospora crassa glycogen synthase encoded by the gsn cDNA. Mol Genet Genomics 267(2):241–253. doi:10.1007/s00438-002-0659-4 PubMedView ArticleGoogle Scholar
- Bardiya N, Shiu PK (2007) Cyclosporin A-resistance based gene placement system for Neurospora crassa. Fungal Genet Biol 44(5):307–314. doi:10.1016/j.fgb.2006.12.011 PubMedView ArticleGoogle Scholar
- Hong CI, Zamborszky J, Baek M, Labiscsak L, Ju K, Lee H et al (2014) Circadian rhythms synchronize mitosis in Neurospora crassa. Proc Natl Acad Sci USA 111(4):1397–1402. doi:10.1073/pnas.1319399111 PubMed CentralPubMedView ArticleGoogle Scholar
- Belden WJ, Larrondo LF, Froehlich AC, Shi M, Chen CH, Loros JJ et al (2007) The band mutation in Neurospora crassa is a dominant allele of ras-1 implicating RAS signaling in circadian output. Genes Dev 21(12):1494–1505. doi:10.1101/gad.1551707 PubMed CentralPubMedView ArticleGoogle Scholar
- Chen CH, DeMay BS, Gladfelter AS, Dunlap JC, Loros JJ (2010) Physical interaction between VIVID and white collar complex regulates photoadaptation in Neurospora. Proc Natl Acad Sci USA 107(38):16715–16720. doi:10.1073/pnas.1011190107 PubMed CentralPubMedView ArticleGoogle Scholar
- Schmoll M, Tian C, Sun J, Tisch D, Glass NL (2012) Unravelling the molecular basis for light modulated cellulase gene expression—the role of photoreceptors in Neurospora crassa. BMC Genom 13:127. doi:10.1186/1471-2164-13-127 View ArticleGoogle Scholar