Cas9-NG Greatly Expands the Targeting Scope of the Genome-Editing Toolkit by Recognizing NG and Other Atypical PAMs in Rice

Apr 1, 2019Molecular plant

Cas9-NG Widens Genome Editing by Targeting More DNA Sites in Rice

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Abstract

Cas9-NG can edit all NGG, NGA, NGT, and NGC sites in transgenic rice, albeit with impaired activity.

Cas9-NG shows nuclease activity towards various NGN PAMs in rice, but primarily results in monoallelic mutations.
Base editors engineered with Cas9-NG successfully created OsBZR1 gain-of-function plants that are not possible with other Cas9 variants.
A transcriptional activator based on Cas9-NG effectively upregulated the expression of endogenous target genes in rice.
Cas9-NG also recognizes additional PAM sequences including NAC, NTG, NTT, and NCG, broadening its application in genome editing.

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CRISPR technologies enabling precise genome manipulation are valuable for gene function studies and molecular crop breeding. However, the requirement of a protospacer adjacent motif (PAM), such as NGG and TTN, for Cas protein recognition restricts the selection of targetable genomic loci in practical applications of CRISPR technologies. Recently Cas9-NG, which recognizes a minimal NG PAM, was reported to expand the targeting space of genome editing in human cells, but it remains unclear whether this Cas9 variant can be used in plants. In this study, we evaluated the nuclease activity of Cas9-NG toward various NGN PAMs by targeting endogenous genes in transgenic rice. We found that Cas9-NG edits all NGG, NGA, NGT, and NGC sites with impaired activity, while the gene-edited plants were dominated by monoallelic mutations. Cas9-NG-engineered base editors were then developed and used to generate OsBZR1 gain-of-function plants that can not be created by other available Cas9-engineered base editors. Moreover, we showed that a Cas9-NG-based transcriptional activator efficiently upregulated the expression of endogenous target genes in rice. In addition, we discovered that Cas9-NG recognizes NAC, NTG, NTT, and NCG apart from NG PAM. Together, these findings demonstrate that Cas9-NG can greatly expand the targeting scope of genome-editing tools, showing great potential for targeted genome editing, base editing, and genome regulation in plants.

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Cas9-NG Greatly Expands the Targeting Scope of the Genome-Editing Toolkit by Recognizing NG and Other Atypical PAMs in Rice

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