**3. Early flowering of horticultural plants through expression of the**  *AtFT* **gene**

FT protein is a mobile signal of flowering. For example, FT induces flowering when a transgenic scion expressing the *FT* gene is grafted onto an *ft* mutant lacking *FT* gene function [32]. FT proteins produced in leaves and stems can contribute to early flowering, as well as FT proteins produced at shoot apices where flowers are formed. FT protein is originally produced in companion cells of the leaf vasculature. Then, the ALSV vector was prepared so that it expresses Arabidopsis *FT* gene (*AtFT*) at the XSB site (**Figure 4A**).

Horticultural plants, such as soybean and Eustoma infected by the ALSV vector expressing *AtFT* generate flowers earlier than normal (**Figure 4B** and **C**) [33, 34]. Such early-flowering plants often set seeds that germinate normally to generate next-generation seedlings. The ALSV vector has therefore successfully shortened the generation times of horticultural plants. Additional example of early-flowering plants is shown in **Figure 5**. These plants flowered at juvenile phase, showing the successful induction of early flowering by the ALSV-XSB(AtFT) vector.

ALSV Vector Substantially Shortens Generation Time of Horticultural Plants http://dx.doi.org/10.5772/intechopen.70317 77

Based on the degree of silencing of the apple *RubisCO small subunit* (*rbcS*) gene with the same 201-base insertion sequence, silencing effects of the three cloning sites differ from one another, and they are greater in the following order: the XSB site > the MN site > the SM site [31]. Again, insertion of a 201-base fragment of the target gene in the XSB site of the ALSV vector is recommended for efficient gene silencing with a lower risk of deletions. The SM site and the MN site are also available to silence additional target genes, by inserting different sequences at each cloning sites. Such simultaneous expression/suppression of different genes is possible, but such vectors typically show low infection rates. The MN site was also used for virus-induced transcriptional gene silencing (VITGS) in *N. benthamiana* and petunia, where upstream sequences (promoters) of the target genes are methylated by virus vectors [20]. The nucleotide sequence of an apple gene

**Figure 3.** Silencing of *PDS* gene by ALSV vector. (A) An ALSV vector having insertion of a 201-base tobacco *PDS* gene fragment [ALSV-XSB(NtPDS-201)]. (B) The ALSV vector was infected into *N. benthamiana*. NI, non-inoculated ('healthy')

promoter was also mutated and inserted at the XSB site for infection to apple plants [15].

**3. Early flowering of horticultural plants through expression of the** 

expresses Arabidopsis *FT* gene (*AtFT*) at the XSB site (**Figure 4A**).

FT protein is a mobile signal of flowering. For example, FT induces flowering when a transgenic scion expressing the *FT* gene is grafted onto an *ft* mutant lacking *FT* gene function [32]. FT proteins produced in leaves and stems can contribute to early flowering, as well as FT proteins produced at shoot apices where flowers are formed. FT protein is originally produced in companion cells of the leaf vasculature. Then, the ALSV vector was prepared so that it

Horticultural plants, such as soybean and Eustoma infected by the ALSV vector expressing *AtFT* generate flowers earlier than normal (**Figure 4B** and **C**) [33, 34]. Such early-flowering plants often set seeds that germinate normally to generate next-generation seedlings. The ALSV vector has therefore successfully shortened the generation times of horticultural plants. Additional example of early-flowering plants is shown in **Figure 5**. These plants flowered at juvenile phase,

showing the successful induction of early flowering by the ALSV-XSB(AtFT) vector.

*AtFT* **gene**

plant.

76 Plant Engineering

**Figure 4.** Early flowering of soybean and Eustoma. (A) Schematic representation of the empty vector (wtALSV) and the vector expressing *AtFT* [ALSV-XSB(AtFT)]. (B) Soybean plants (cultivar 'Tanba-Guro') 1 month after inoculation of germinated seeds. (C) Eustoma (Lisianthus) plants 2 months after inoculation of 1-month-old seedlings.

**Figure 5.** Additional example of early-flowering plants. Petunia seedlings which exhibit early flowering via infection by the ALSV-XSB(AtFT) vector. Left plants are infected by wtALSV. The photograph was originally reported in Ref. [10].
