Overexpression of Arabidopsis FT gene in apple leads to perpetual flowering

Abstract

Transgenic apple plants that overexpressed Arabidopsis FLOWERING LOCUS T (FT) under the control of the rolC promoter showed early flowering, while the introduction of FT driven by the 35S promoter induced flower development directly from transgenic apple callus in vitro, but vegetative growth was not maintained and the explant died. GFP-FT fusion proteins were detectable in transgenic apple tissues but never caused early flowering in the transformants. Under the control of the rolC promoter, the fused protein was localized in vascular tissues and fluorescence was detectable in companion cells in the stem and petiole. The transgenic apple lines that expressed AtFT driven by the rolC promoter showed differences in inflorescence architecture and floral organ number from those typical of nontransformed apple. Flowers of transgenic apple lines often contained more numerous petals, fewer stamens, and no pistils, and the pollen grains were incapable of germinating. The transgenic apple lines showed perpetual flowering without the requirement for low temperature and obvious photoperiodism. The expression patterns of six floral meristem identity genes and floral organ genes in flowers of transgenic apple lines were investigated. Among the floral meristem identity genes, expression of MdFT2 was suppressed and that of AFL2 was dramatically enhanced in the transformants. Of the floral organ genes, expression of MdMADS13, which functions as a class B gene, was unchanged from that of the flower of wild type one, whereas expression of MdMADS-NB, a possible class C gene, was suppressed.

Overexpression of Arabidopsis FLOWERING LOCUS T (FT) gene improves floral development in cassava (Manihot esculenta, Crantz)

“…curcas to demonstrate enhanced flowering [ 10 ], and FT overexpression in various paired species has accelerated flowering in apple ( Malus spp.) [ 16 , 17 ], and poplar ( Populus trichocarpa ) [ 18 ]. Given the effectiveness of this approach, it has been suggested that FT overexpression could be used to hasten flowering in breeding programs [ 15 , 18 – 20 ].…”

The analysis of transgenic apples with down-regulated expression of <i>MdPISTILLATA</i>

“…But the transgenic apple hardly showed fertility compared with 'Spencer Seedless. ' By contrast, line 213 of the rolC:AtFT/1P-2:antisense-MdPI transgenic apple had pinkish sepaloid petals, stamens, and fewer pistils ( Figure 2F), while line 284 flowers ( Figure 2D) appeared to have the same phenotype as line 66 rolC:AtFT transgenic apple flowers ( Figure 2B), which had accelerated flowering (Tanaka et al 2014). Northern hybridization indicated that the expression of MdPI in line 9-2 was approximately ten times weaker than in the other transgenic lines and the normal cultivars (Figure 3).…”

“…The MdPI promoter region was then inserted into the pSMAK antisense MdPI vector at the HindIII and SpeI sites, and the resultant product was designated pSMAK 1P-2:antisense-MdPI. To accelerate flowering in the transgenic apple, a rolC:AtFT was added to the pSMAK 1P-2:antisense-MdPI vector at the HindIII site (Tanaka et al 2014). The resultant vector was designated pSMAK rolC:AtFT/1P-2:antisense-MdPI (Figure 1), which was intended to cause flowering acceleration and the specific suppression of MdPI in transgenic apple.…”

Expression and functional analysis of apple <i>MdMADS13</i> on flower and fruit formation

“…The amplified DNA fragment was 170 bp. Specific primers for MdFT2 were used as described in an earlier report (Tanaka et al 2014). Apple ubiquitin (MdUBQ) was quantified as an internal control, as explained in an earlier report of the literature (Takos et al 2006).…”