Abstract
In plants, successful reproduction requires the proper timing of flowering under changing environmental conditions. Arabidopsis FLOWERING LOCUS T (FT), which encodes a proposed phloem-mobile florigen, has a close homologue, TWIN SISTER OF FT (TSF). During the vegetative phase, TSF shows high levels of expression in the hypocotyl before FT induction, but the tsf mutation does not have an apparent flowering-time phenotype on its own under long-day conditions. This study compared the protein mobility of FT and TSF. With TSF-overexpressing plants as the rootstock, the flowering time of ft tsf scion plants was only slightly accelerated. Previous work has shown that FT is graft-transmissible; by contrast, this study did not detect movement of TSF from the roots into the shoot of the scion plants. This study used plants overexpressing FT/TSF chimeric proteins to map a region responsible for FT movement. A chimeric TSF with region II of FT (L28 to G98) expressed in the rootstock caused early flowering in ft tsf scion plants; movement of the chimeric protein from the rootstocks into the shoot apical region of the ft tsf scion plants was also detected. Misexpression of TSF in the leaf under the control of the FT promoter or grafting of 35S::TSF cotyledons accelerated flowering of ft-10 plants. FT was more stable than TSF. Taking these results together, we propose that protein mobility of FT is higher than that of TSF, possibly due to a protein domain that confers mobility and/or protein stability.
Highlights
The ability to adjust the timing of flowering under continuously changing environmental conditions is important for successful reproduction in plants
Plants (Kobayashi et al, 1999; Yamaguchi et al, 2005). These analyses revealed that used TWIN SISTER OF FT (TSF)-overexpressing plants that showed very strong early flowering were used as rootstock, grafted scion plants did not show a substantial change in flowering time, in sharp contrast to the dramatic acceleration in flowering time observed in scion plants grafted to 35S::FLOWERING LOCUS T (FT) plants
The 35S::FT:T7>ft-10 plants flowered with 21.9 ± 4.2 leaves (Fig. 4C), whereas 35S::TSF:T7>ft-10 plants flowered with 26.3 ± 4.2 leaves These results suggested that grafting a 35S::FT cotyledon led to a stronger acceleration of flowering than grafting a 35S::TSF cotyledon (P
Summary
The ability to adjust the timing of flowering under continuously changing environmental conditions is important for successful reproduction in plants. Extensive molecular genetic analyses using Arabidopsis thaliana have suggested that flowering time is controlled by multiple, interdependent genetic pathways, including the photoperiod, autonomous, vernalization, gibberellic acid, and ambient temperature pathways (Amasino and Michaels, 2010).
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