4. Post-translational regulation of FT
Determination of the endogenous levels of FT s in plant is a challenging task because it is difficult to raise antibodies which can be used for the mentioned purpose due to the high amino acid resemblance of FT homologs. Recently in a study, Ahn’s group has reported an antibody which has been generated against a very short peptide ofFT in Arabidopsis thaliana . This antibody enabled them to find out that the abundance of FT increases before the blooming of plants begin and gradually decreases then, although continuous transcription of FT mRNA in a short period may lead to an uncoupling of mRNA level and protein. According to these findings, much faster transcription of FT has been observed than its degradation after the variation in photoperiod (Kim et al., 2016). Even though, it has not been appear that there is some effect of ubiquitination pathway on FT degradation, an unknown serine/cysteine protease has been attached between E167 and S168 in the cleavage of FT (Figure 2) (Kim et al., 2016). Along with these evidences that the cleavage of seven amino acids from C-terminus is essential for the transport ofFT , these results proposed that the proteolytic truncation ofFT is significant in A. thaliana. The in-depth knowledge about the appropriate protease may be helpful to explain FThydrolysis in detail.
Keeping in mind the post-transcriptional modification of animal PEBPs signaling activities with the binding of phosphatidylethanolamine (PE), Nakamura along with colleagues suggested that binding of small lipids may modulate plant FT functions. They observed in their in vitro experimental study that phosphatidylcholine (PC) binds to FT in A. thaliana, instead of PE (Figure 2) (Nakamura et al., 2014). It has been reported with a transgenic analyses that flowering has been promoted with the increased abundance of PC in shoot meristem but this may be mitigated with the compromised activity of FT . Additional study demonstrated that diurnal oscillation of PC content was crucial for the activity of FT , as day-dominant PC species bind byFT to promote flowering (Nakamura et al., 2014). Thus, small molecules binding by FT may be a superfluous way to specifically control blooming time.