Listening to the silent genes: transgene silencing, gene regulation and pathogen control

By capitalizing on the initially puzzling observations of unpredictable tra nsgene silencing and variable expression, plant scientists have pioneered r esearch into a navel type of epigenetic regulation, termed homology-depende nt gene silencing. This silencing process has implications for natural mech anisms of gene expression in plants and other eukaryotes, and has branched out into studies of reversible DNA modifications; RNA metabolism, transport and processing; and host responses to plant viruses, viroids and transposa ble elements. The analysis of transgene silencing systems has enriched our understanding of other epigenetic phenomena, including paramutation, as wel l as heterosis and genome evolution. This research is also highly relevant to the biotechnology industry, which is interested in avoiding unwanted tra nsgene silencing in genetically engineered lines and in exploiting various types of silencing to inactivate specific genes, Homology-dependent gene si lencing can also be used in high-throughput approaches for functional genom ics.