Possibly has a role in RNA transcription or processing during stress (PubMed:16207746). Binds sequence non-specifically to RNAs and DNAs (PubMed:16207746). Mediates cell-to-cell trafficking of RNA interference (RNAi) signals (small RNAs (sRNA), e.g. small interfering RNA (siRNA) and microRNA (miRNA)) which regulate growth and development, as well as responses to environmental inputs, including pathogen attack; can compromise zucchini yellow mosaic virus (ZYMV) and tobacco rattle virus (TRV) infections at the early stage (PubMed:31812689). Binds to small phloem-mobile single-stranded RNAs (ss-sRNA, e.g. small interfering RNA (siRNA) and microRNA (miRNA)) in the phloeme exudate, including viral-derived sRNA (vsiRNA). Observed in the phloem translocation stream. Abundantly expressed in young plants, root tips, and flowers, but weakly in mature leaves and stems, implying highly expression in actively proliferating organs. Up-regulated by cold stress and down-regulated by salt stress and dehydration stress. The glycine-rich (GR) domain is necessary and sufficient for cell-to-cell movement and to interefere with zucchini yellow mosaic virus (ZYMV) infection. Plants overexpressing RBG4 display retarded germination under salt and dehydration stress. Belongs to the GR-RBP family.