Silencing of potato virus X coat protein gene in transgenic tobaccos by codon replacement that confers resistance to PVX infection

To understand the effect of rare codon on the silencing ratio of foreign gene, some preferred codon in potato virus X (PVX) coat protein gene (cp) were substituted with synonymous rare codons. The modified PVX coat protein gene (cpm) and wild-typecp gene (cpw) were inserted into binary vector under the control of CaMV35S promoter, and these two plant expression constructs were transferred into tobacco (Nicotiana tabacum cv. Xanthi) genomesvia Agrobacterium mediated method and transgenic plants were generated. Northern blot analysis of RNA isolated from these plants showed that the silencing ratio ofcpm gene in transgenic tobaccos was higher than that ofcpw (35% and 6.25% respectively). Run on results indicate that the silencing ofcp gene happened at post-transcriptional level. The resistance of transgenic tobaccos carryingcpm genes to PVX is increased compared with that of transformants carryingcpw genes. These results suggest that the resistance of transgenic tobacco to PVX can be enhanced by codon replacement.