系統性訊息核醣核酸: FLOWERING LOCUS T訊息核醣核酸長距離運輸的功能與機制

Abstract

The systemic signaling system is an important mechanism which helps plants to communicate and orchestra the development with external and internal cues. 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 reveled that the FLOWERING LOCUS T (FT) protein is a systemic florigenic signal. However, whether the FT mRNA also participates in systemic floral regulation remains controversial. In this study, by using Arabidopsis cleft-grafting experiments, we showed that the mRNA 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 mRNA for long-distance movement. Therefore, FT mRNA is a bona fide non-cell-autonomous mRNA. To examine the systemic action of FT mRNA, we uncoupled the movement of FT mRNA from protein by fusing FT with a 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 mRNA by RNAi or artificial miRNA against FT delayed the floral promotion, indicating that the translocated FT mRNA acts as a part of the systemic floral signaling. Our results indicate that both FT mRNA and protein move long distance and act redundantly to integrate the photoperiodic signals. In addition, little is known about how plants regulate the movement of mRNA. To further analyze the mechanism underlying mRNA movement, we developed two visualization-based screening systems to further identify putative non-cell-autonomous mRNAs. We further characterized the correlation between RNA size and the movement of non-cell-autonomous RNA, and the translational ability of the translocated mRNA.