CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes.
CRISPR-mediated interference relies on complementarity between a guiding CRISPR RNA (crRNA) and target nucleic acids to provide defense against bacteriophage. Phages escape CRISPR-based immunity mainly through mutations in the protospacer adjacent motif (PAM) and seed regions. However, previous spec...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Public Library of Science (PLoS)
2023-04-01
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| Series: | PLoS Biology |
| Online Access: | https://doi.org/10.1371/journal.pbio.3002065 |
| _version_ | 1797832296714207232 |
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| author | Michael A Schelling Giang T Nguyen Dipali G Sashital |
| author_facet | Michael A Schelling Giang T Nguyen Dipali G Sashital |
| author_sort | Michael A Schelling |
| collection | DOAJ |
| description | CRISPR-mediated interference relies on complementarity between a guiding CRISPR RNA (crRNA) and target nucleic acids to provide defense against bacteriophage. Phages escape CRISPR-based immunity mainly through mutations in the protospacer adjacent motif (PAM) and seed regions. However, previous specificity studies of Cas effectors, including the class 2 endonuclease Cas12a, have revealed a high degree of tolerance of single mismatches. The effect of this mismatch tolerance has not been extensively studied in the context of phage defense. Here, we tested defense against lambda phage provided by Cas12a-crRNAs containing preexisting mismatches against the genomic targets in phage DNA. We find that most preexisting crRNA mismatches lead to phage escape, regardless of whether the mismatches ablate Cas12a cleavage in vitro. We used high-throughput sequencing to examine the target regions of phage genomes following CRISPR challenge. Mismatches at all locations in the target accelerated emergence of mutant phage, including mismatches that greatly slowed cleavage in vitro. Unexpectedly, our results reveal that a preexisting mismatch in the PAM-distal region results in selection of mutations in the PAM-distal region of the target. In vitro cleavage and phage competition assays show that dual PAM-distal mismatches are significantly more deleterious than combinations of seed and PAM-distal mismatches, resulting in this selection. However, similar experiments with Cas9 did not result in emergence of PAM-distal mismatches, suggesting that cut-site location and subsequent DNA repair may influence the location of escape mutations within target regions. Expression of multiple mismatched crRNAs prevented new mutations from arising in multiple targeted locations, allowing Cas12a mismatch tolerance to provide stronger and longer-term protection. These results demonstrate that Cas effector mismatch tolerance, existing target mismatches, and cleavage site strongly influence phage evolution. |
| first_indexed | 2024-04-09T14:05:33Z |
| format | Article |
| id | doaj.art-7bb3d5b18739470cbab4690808c2ebcd |
| institution | Directory Open Access Journal |
| issn | 1544-9173 1545-7885 |
| language | English |
| last_indexed | 2024-04-09T14:05:33Z |
| publishDate | 2023-04-01 |
| publisher | Public Library of Science (PLoS) |
| record_format | Article |
| series | PLoS Biology |
| spelling | doaj.art-7bb3d5b18739470cbab4690808c2ebcd2023-05-07T05:30:38ZengPublic Library of Science (PLoS)PLoS Biology1544-91731545-78852023-04-01214e300206510.1371/journal.pbio.3002065CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes.Michael A SchellingGiang T NguyenDipali G SashitalCRISPR-mediated interference relies on complementarity between a guiding CRISPR RNA (crRNA) and target nucleic acids to provide defense against bacteriophage. Phages escape CRISPR-based immunity mainly through mutations in the protospacer adjacent motif (PAM) and seed regions. However, previous specificity studies of Cas effectors, including the class 2 endonuclease Cas12a, have revealed a high degree of tolerance of single mismatches. The effect of this mismatch tolerance has not been extensively studied in the context of phage defense. Here, we tested defense against lambda phage provided by Cas12a-crRNAs containing preexisting mismatches against the genomic targets in phage DNA. We find that most preexisting crRNA mismatches lead to phage escape, regardless of whether the mismatches ablate Cas12a cleavage in vitro. We used high-throughput sequencing to examine the target regions of phage genomes following CRISPR challenge. Mismatches at all locations in the target accelerated emergence of mutant phage, including mismatches that greatly slowed cleavage in vitro. Unexpectedly, our results reveal that a preexisting mismatch in the PAM-distal region results in selection of mutations in the PAM-distal region of the target. In vitro cleavage and phage competition assays show that dual PAM-distal mismatches are significantly more deleterious than combinations of seed and PAM-distal mismatches, resulting in this selection. However, similar experiments with Cas9 did not result in emergence of PAM-distal mismatches, suggesting that cut-site location and subsequent DNA repair may influence the location of escape mutations within target regions. Expression of multiple mismatched crRNAs prevented new mutations from arising in multiple targeted locations, allowing Cas12a mismatch tolerance to provide stronger and longer-term protection. These results demonstrate that Cas effector mismatch tolerance, existing target mismatches, and cleavage site strongly influence phage evolution.https://doi.org/10.1371/journal.pbio.3002065 |
| spellingShingle | Michael A Schelling Giang T Nguyen Dipali G Sashital CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes. PLoS Biology |
| title | CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes. |
| title_full | CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes. |
| title_fullStr | CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes. |
| title_full_unstemmed | CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes. |
| title_short | CRISPR-Cas effector specificity and cleavage site determine phage escape outcomes. |
| title_sort | crispr cas effector specificity and cleavage site determine phage escape outcomes |
| url | https://doi.org/10.1371/journal.pbio.3002065 |
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