Recombinase Polymerase Amplification Assay with and without Nuclease-Dependent-Labeled Oligonucleotide Probe.

The combination of recombinase polymerase amplification (RPA) and lateral flow test (LFT) is a strong diagnostic tool for rapid pathogen detection in resource-limited conditions. Here, we compared two methods generating labeled RPA amplicons following their detection by LFT: (1) the basic one with primers modified with different tags at the terminals and (2) the nuclease-dependent one with the primers and labeled oligonucleotide probe for nuclease digestion that was recommended for the high specificity of the assay. Using both methods, we developed an RPA-LFT assay for the detection of worldwide distributed phytopathogen-alfalfa mosaic virus (AMV). A forward primer modified with fluorescein and a reverse primer with biotin and fluorescein-labeled oligonucleotide probe were designed and verified by RPA. Both labeling approaches and their related assays were characterized using the in vitro-transcribed mRNA of AMV and reverse transcription reaction. The results demonstrated that the RPA-LFT assay based on primers-labeling detected 10 copies of RNA in reaction during 30 min and had a half-maximal binding concentration 22 times lower than probe-dependent RPA-LFT. The developed RPA-LFT was successfully applied for the detection of AMV-infected plants. The results can be the main reason for choosing simple labeling with primers for RPA-LFT for the detection of other pathogens.