On occassion, virus-derived transgenes in plants can be poorly expressed and yet provide excellent virus resistance, and transgene constructs designed to supplement the expression of endogenous genes can have the effect of co-suppressing themselves and the endogenous genes. These two phenomena appear to result from the same poet-transcriptional silencing mechanism, which operates by targeted-RMA degradation. Recent research into RNA-mediated virus resistance and co-suppression has provided insights into the interactions between plant Viruses and their hosts, and spawned several models to explain the phenomenon.