SPAAC-NAD-seq, a sensitive and accurate method to profile NAD+-capped transcripts

We developed a Copper-free, strain-promoted azide-alkyne cycloaddition reaction (SPAAC) to capture NAD-RNAs without RNA degradation. We examined the specificity of CuAAC and SPAAC reactions towards NAD+ vs. m7G, and found that both prefer NAD+ but also act on m7G. We show that m7G-capped RNA can be immuno-depleted, allowing for the specific identification of NAD-RNA via the SPAAC reaction and sequencing, which we name SPAAC-NAD-seq. Subjecting Arabidopsis RNA to both the original NAD captureSeq and SPAAC-NAD-seq, we found that more NAD+-capped RNA was identified by the latter, particularly those with low abundance. This led to the discovery of new gene ontology terms such as starch biosynthsis, intracellular protein transport and response to cadmium stress associated with genes that produce NAD-RNA. Furthermore, reads were uniformly distributed along gene bodies, which suggested that SPAAC-NAD-seq retained full-length sequence information. SPAAC-NAD-seq enables specific and efficient discovery of NAD-RNA in prokaryotes, and when combined with m7G-RNA depletion, in eukaryotes. NAD capped transcripts profiled by CuAAC-NAD-seq and SPAAC-NAD-seq in Arabidopsis