Alternative miRNAs: Human sequences misidentified as plant miRNAs in plant studies and in human plasma

A recent study reported that “Plant miRNAs found in human circulating system provide evidences of cross kingdom RNAi” 1 . Analysis of two human blood plasma sequencing datasets was said to provide evidence for uptake of plant miRNAs into human plasma. The results were also purportedly inconsistent with contamination 1 . However, a review of these data suggests that they do not support dietary xenomiR uptake, but instead confirm previous findings that detection of rare plant miRNAs in mammalian sequencing datasets is artifactual. Only one putative plant miRNA (“peu-MIR2910) in this study mapped consistently above background, and this sequence is found in a human rRNA. Several other rarer but consistently mapped plant miRNAs also have 100% or near 100% matches to human transcripts or genomic sequences, and some do not map to plant genomes at all. These misidentified “alternative miRNAs”—including MIR2910 and MIR2911—emphasize the need for rigorous filtering strategies when assessing possible xenomiRNAs.