The florigen mystery. A potential solution for an ancient riddle.

摘要

Florigen is a flower forming substance produced when leaves are exposed to light. Recently, a seemingly significant breakthrough in unravelling the identity of florigen occurred when a mysterious flowering signal was reported that could after all be the mRNA of the flowering locus (FT) gene, one of the 2 genes that had been identified to be critical to photoperiod-induced flowering in Arabidopsis thaliana. Starting with a photoresponsive species, where phloem sap collection is easy, one could develop a transgenic overexpressing the FT mRNA. The scion of the wild type of the same species can be grafted onto the stock of the FT transgenic to prove the movement of the FT mRNA from an induced tissue, through the phloem cells. Since the flowering signal is known to travel along with photosynthates in the phloem, analysis of the phloem sap from above the grafted portion for the presence of FT mRNA and protein, could be an ideal technique to unravel the identity of florigen. Real-time PCR analysis using cDNA synthesized molecular beacons (MB) complementary to the target FT mRNA region, could be used to conclusively prove the nature of the phloem-transmitted flowering signal. MB, a relatively new tool for highly sensitive and specific real-time molecular recognition, are a class of DNA probes, which are single-stranded oligonucleotides with a stem and loop structure. The primary advantage of the MB probe is that because of the low background signal, it displays an enhanced fluorescence upon hybridizing with the target sequence, which allows it to function as a highly selective probe for real-time monitoring. Another important advantage of the MBs are their molecular recognition specificity. MBs are extremely target specific, ignoring target sequences that vary as little as a single nucleotide. MBs have also been reported to help in visualizing mRNA in living systems. This property could be used for detecting the presence of FT mRNA in the live shoot apex of the phloem, after photoinduction, in addition to the detection of the presence of FT::GFP protein. MBs offer a potential technique to monitor the presence of FT mRNA in the leaves and the shoot apex, in real time, similar to the use of GFP.