Efficient virus-induced gene silencing in apple, pear and Japanese pear using Apple latent spherical virus vectors

Background: Virus-induced gene silencing (VIGS) is an effective technology for the analysis of gene functions in plants. Though there are many reports on virus vectors for VIGS in plants, no VIGS vectors available for Rosaceae fruit trees were reported so far. We present an effective VIGS system in apple, pear, and Japanese pear using Apple latent spherical virus (ALSV) vectors. Results: Inoculation of ALSV vectors carrying a partial sequence of endogenous genes from apple [ribulose-1, 5-bisphosphate carboxylase small subunit (rbcS), alpha subunit of chloroplast chaperonin (CPN60 alpha), elongation factor 1 alpha (EF-1 alpha), or actin] to the cotyledons of seeds by a particle bombardment induced highly uniform knock-down phenotypes of each gene on the true leaves of seedlings from 2 similar to 3 weeks after inoculation. These silencing phenotypes continued for several months. Northern blot and RT-PCR analyses of leaves infected with ALSV containing a fragment of rbcS gene showed that the levels of rbcS-mRNA drastically decreased in the infected apple and pear leaves, and, in reverse, rbcS-siRNAs were generated in the infected leaves. In addition, some of apple seedlings inoculated with ALSV vector carrying a partial sequence of a TERMINAL FLOWER 1 gene of apple (MdTFL1) showed precocious flowering which is expected as a knock-down phenotype of the silencing of MdTFL1 gene. Conclusions: The ALSV-based VIGS system developed have provides a valuable new addition to the tool box for functional genomics in apple, pear, and Japanese pear.