Long-distance movement of Arabidopsis FLOWERING LOCUS T RNA participates in systemic floral regulation

The finding of mRNA acting as a systemic information molecule is one of the most exciting discoveries in recent plant biology. However, evidence demonstrating the functional significance of non-cell autonomous RNA remains limited. Recent analyses of Arabidopsis and rice revealed FLOWERING LOCUS T (FT) protein as a systemic florigenic signal. However, whether the FT RNA also participates in systemic floral regulation remains controversial. By using Arabidopsis cleft-grafting experiments, we showed that the RNA of Arabidopsis FT undergoes long-distance movement from the stock to the scion apex in both FT transformants and non-transformants. In addition, the sequences of FT RNA are sufficient to target a cell-autonomous RNA for long-distance movement. Therefore, FT RNA is a bona fide non-cell autonomous RNA. To examine the systemic action of FT RNA, we uncoupled the movement of FT RNA from protein by fusing FT with RED FLUORESCENT PROTEIN (RFP). When RFP-FT protein was retained in companion cells, the detection of RFP-FT RNA correlates with floral promotion in the scion. Further depletion of the translocated RFP-FT RNA by RNAi or artificial miRNA against FT delayed the floral promotion, indicating that the translocated FT RNA acts as a part of the systemic floral signaling. Our results indicate that both FT RNA and protein move long distance and act redundantly to integrate the photoperiodic signals.