First report of CRISPR/Cas13a-based rapid detection of groundnut bud necrosis virus without amplification.

Globally, the groundnut bud necrosis virus (GBNV) (Bunyaviridae), pose a serious threat to solanaceous and leguminous crops causing serious crop loss. This requires a rapid and sensitive diagnostics for initially identifying at the earliest stage and further to initiate disease management. This study presents the first report of a CRISPR/Cas13a-based diagnostic assay for GBNV detection without amplification. GBNV was maintained in cowpea cv. C152 through mechanical inoculation, further viral RNA was isolated to clone the two target genes viz. nucleocapsid (NP) and movement protein (MP) genes. These genes were ligated to pTZ57R/T vector and sequenced. Similarly, the LshCas13a gene was cloned from pUC19 into pET28a, expressed in E. coli BL21, and purified using Ni-NTA affinity chromatography. Guide RNAs targeting conserved regions of NP and MP genes were synthesized by in vitro transcription and mixed with Cas13a protein to form ribonucleoprotein (RNP) complex. Target RNA, obtained either by in vitro-transcription or crude extract of infected tomato was used to detect GBNV, using a fluorescence-based reporter assay. This method found to be highly sensitive that could detect GBNV at as low as 0.01 ng. From the field perspective, GBNV could be detected from the crude extract of the GBNV infected tomato leaves using an alkaline PEG buffer. Thus CRISPR/Cas13a-based assay provides a rapid, amplification-free, and field-deployable diagnostic platform for GBNV. This lays the groundwork for a field adoptable CRISPR diagnostics for other plant RNA viruses also.