In plants,RNA interference (RNAi) plays a pivotal role in growth and development,and responses to environmental inputs,including pathogen attack.The intercellular and systemic trafficking of small interfering RNA (siRNA)/microRNA (miRNA) is a central component in this regulatory pathway.Currently,little is known with regards to the molecular agents involved in the movement of these si/miRNAs.To address this situation,we employed a biochemical approach to identify and characterize a conserved SMALL RNA-BINDING PROTEIN 1 (SRBP1) family that mediates non-cell-autonomous small RNA (sRNA) trafficking.In Arabidopsis,AtSRBP1 is a glycine-rich (GR) RNA-binding protein,also known as AtGRP7,which we show binds single-stranded siRNA.A viral vector,Zucchini yellow mosaic virus (ZYMV),was employed to functionally characterized the AtSRBP1-4 (AtGRP7/2/4/8) RNA recognition motif and GR domains.Cellular-based studies revealed the GR domain as being necessary and sufficient for SRBP1 cell-to-cell movement.Taken together,our findings provide a foundation for future research into the mechanism and function of mobile sRNA signaling agents in plants.