Small RNAs (sRNAs) that are 21 to 24 nucleotides (nt) in length are found in most
eukaryotic organisms and regulate numerous biological functions, including transposon
silencing, development, reproduction, and stress responses, typically via control
of the stability and/or translation of target mRNAs. Major classes of sRNAs in plants
include microRNAs (miRNAs) and small interfering RNAs (siRNAs); sRNAs are known to
travel as a silencing signal from cell to cell, root to shoot, and even between host
and pathogen. In mammals, sRNAs are transported inside extracellular vesicles (EVs),
which are mobile membrane-bound compartments that participate in intercellular communication.
In addition to sRNAs, EVs carry proteins, lipids, metabolites, and potentially other
types of nucleic acids. Here we report that Arabidopsis (Arabidopsis thaliana) EVs
also contain diverse species of sRNA. We found that specific miRNAs and siRNAs are
preferentially loaded into plant EVs. We also report a previously overlooked class
of "tiny RNAs" (10 to 17 nt) that are highly enriched in EVs. This RNA category of
unknown function has a broad and very diverse genome origin and might correspond to
degradation products.