TOWARDS GENE SILENCING IN ONION

Gene silencing or gene knockdown through the use of RNA interference (RNAi) technology has become a major tool in the elucidation of genetic and biochemical steps in higher organisms (Wesley et al., 2001; Smith et al., 2000; Chen et al., 2003). To date, the technology has been applied mainly to model systems such as Arabidopsis. There are several difficulties in applying this technology to recalcitrant crop species such as onion. For example the low transformation efficiency of onion compared to model systems and lengthy regeneration times mean that great effort is required to produce a few transformants. As silencing efficiency varies between individual transgenic events it may be necessary to produce many transformants or fuse the silencing signal to a reporter gene silencing signal and co-silence a reporter gene. This then requires a ready supply of material expressing a reporter gene for transformation. If only a few transformants are produced is this because the RNAi construct is detrimental to survival. If no phenotype is detected does this mean that the silencing signal is not working, or are alternative steps circumventing the process under scrutiny? A simple way to answer these questions is to develop a transient silencing signal. Here we report the first steps towards such a system.