Application of cucumber mosaic virus to efficient induction and long-term maintenance of virus-induced gene silencing in spinach.

Virus-induced gene silencing (VIGS) is a useful tool for functional genomics in plants. In this study, we tried to apply cucumber mosaic virus (CMV) to efficient induction of VIGS in spinach. Although VIGS for spinach had been previously developed based on two viruses (beet curly top virus and tobacco rattle virus), they still have some problems with systemic movement and long-term maintenance of VIGS in spinach. Although ordinary CMV strains infect spinach inducing distinct mosaic symptoms, using a CMV pseudorecombinant, we can modify the viral pathogenicity to attenuate viral symptoms that may mask the silencing phenotype. We here successfully demonstrated the viral ability to silence the phytoene desaturase (PDS) and the dihydroflavonol 4-reductase (DFR) genes in spinach. Because CMV could quickly induce VIGS even at 7-10 days postinoculation and the virus did not disappear even at the flowering stage, this CMV-based VIGS system would contribute to functional genomics in spinach and especially to the elucidation of molecular mechanisms for some properties unique to spinach such as plasticity of sex expression; the CMV-induced VIGS can last until the flowering stage after the virus was inoculated onto the seedling.