Apple latent spherical virus (ALSV) vector is a convenient alternative to genetic transformation in horticultural plants, especially in species recalcitrant to genetic transformation. ALSV, an RNA virus, can infect a wide variety of plant species including major horticultural plants without inducing symptoms. Here, methodologies were developed for infection of ALSV vectors to strawberry seedlings and plantlets cultured in vitro. A seed-propagated F1 hybrid strawberry cultivar 'Yotsuboshi' was aseptically grown on half-strength Murashige–Skoog medium for 1 month and true leaves were inoculated with an ALSV RNA preparation by particle bombardment. ALSV vector infection rates varied from 58 to 100% according to the insertion sequences, in ‘Yotsuboshi’ seedlings. Plantlets (‘Dover’) propagated in vitro could also be infected with ALSV vector at a similar infection rate. For virus-induced gene silencing (VIGS), we prepared an ALSV vector carrying a 201 nucleotide segment of the strawberry phytoene desaturase gene. ‘Yotsuboshi’ and ‘Dover’ plants infected by this vector generated completely white leaves at fifth or sixth true leaves and above. For virus-induced flowering (VIF), we used an ALSV vector expressing the Arabidopsis thaliana flowering locus T gene. Strawberry seedlings infected by this vector started to flower from about 2 months post inoculation and bore fruits with viable seeds. The ALSV vector was no longer detected in any of the seedlings from early-flowered strawberries. Thus, the ALSV vector may be beneficial for examination of gene functions by VIGS in strawberry, and VIF using ALSV vector constitutes an effective new plant breeding technique for the promotion of cross-breeding in strawberry.
Viral vectors: Easy gene modification in strawberries: Apple latent spherical virus (ALSV) offers a powerful tool to reveal strawberry gene function and induce early flowering. Preferential strawberry traits are highly influenced by their genetics; however, the specific mutations that change these traits are largely unknown. This prompted Nobuyuki Yoshikawa and his team from Iwate University, Japan, to develop ALSV to infect and introduce intended genetic material into strawberries. Infecting in vitro cultured plants at a rate of 58—100%, ALSV-vectored gene introduction proved able to ‘silence’ a natural strawberry gene, constituting a method to identify gene functions. The infection was not pathogenic and did not carry on to the plants’ progeny. The team also used ALSV to introduce a gene that induced flowering 2 months post inoculation, a technique that could be used in future to promote shorter cross-breeding times.