FE, a phloem‐specific Myb‐related protein, promotes flowering through transcriptional activation of FLOWERING LOCUS T and FLOWERING LOCUS T INTERACTING PROTEIN 1

Abstract

SUMMARYIn many flowering plants, the transition to flowering is primarily affected by seasonal changes in day length (photoperiod). An inductive photoperiod promotes flowering via synthesis of a floral stimulus, called florigen. In Arabidopsis thaliana, the FLOWERING LOCUS T (FT) protein is an essential component of florigen, which is synthesized in leaf phloem companion cells and is transported through phloem tissue to the shoot apical meristem where floral morphogenesis is initiated. However, the molecular mechanism involved in the long-distance transport of FT protein remains elusive. In this study, we characterized the classic Arabidopsis mutant fe, which is involved in the photoperiodic induction of flowering, and showed that FE encodes a phloem-specific Myb-related protein that was previously reported as ALTERED PHLOEM DEVEL-OPMENT. Phenotypic analyses of the fe mutant showed that FT expression is reduced in leaf phloem companion cells. In addition, the transport of FT protein from leaves to the shoot apex is impaired in the fe mutant. Expression analyses further demonstrated that FE is also required for transcriptional activation of FLOWERING LOCUS T INTERACTING PROTEIN 1 (FTIP1), an essential regulator for selective trafficking of the FT protein from companion cells to sieve elements. These findings indicate that FE plays a dual role in the photoperiodic induction of flowering: as a transcriptional activator of FT on the one hand, and its transport machinery component, FTIP1, on the other hand. Thus, FE is likely to play a role in regulating FT by coordinating FT synthesis and FT transport in phloem companion cells.

Circadian Clock and Photoperiodic Flowering in Arabidopsis: CONSTANS Is a Hub for Signal Integration

“…FTIP1, which is localized in the ER in companion cells, and in the plasmodesmata between companion cells and sieve elements, interacts with FT protein in plasmodesmata, and it is required for FT export from companion cells to the sieve elements (Liu et al, 2012). Although FTIP1 expression is not affected by photoperiod (Liu et al, 2012), the phloem-expressed MYB transcription factor FE/ ALTERED PHLOEM DEVELOPMENT, which contributes to FT expression in long days, is required for the expression of FTIP1 (Abe et al, 2015), indicating the connection of FT induction and FT movement. There is another example for this connection.…”

Transient activity of the florigen complex during the floral transition in Arabidopsis thaliana

“…To construct the p35S::FD-GR, the GR fragment [amplified from the p35S:: FE-GR (Abe et al, 2015) using the primer set GR-up and GR-low] and the FD cDNA fragment (amplified by PCR using the primer set FD-up and FD-low) were cloned into the XbaI/SacI-digested pBI121 using an In-fusion HD Cloning Kit.…”

“…The photoperiod-dependent flowering of Arabidopsis thaliana is controlled primarily by FLOWERING LOCUS T (FT) (Kardailsky et al, 1999;Kobayashi et al, 1999). Long-day conditions (LD) induce FT transcription in leaf phloem companion cells (Abe et al, 2015;Adrian et al, 2010;Notaguchi et al, 2008;Yamaguchi et al, 2005) and the resulting FT protein is transported to the shoot apex, in which it initiates floral development (Abe et al, 2015;Corbesier et al, 2007;Jaeger and Wigge, 2007;Notaguchi et al, 2008). There is increasing evidence that the phosphatidylethanolamine-binding protein encoded by FT, and the proteins that are encoded by homologous genes in other species, are essential components of a mobile floral stimulus (i.e.…”

FT and florigen long-distance flowering control in plants

“…It is an ER-localised membrane protein with a PRT_C membrane-targeting domain and predicted C2 domains reminiscent of membrane-trafficking synaptotagmins and may function as a movement chaperone for FT [19,41]. FE, the last of the classical flowering time genes [5] to be molecularly characterised, encodes a MYB-like transcription factor expressed in the phloem [42 ]. By promoting the transcription of both FTIP and FT in long days, FE positively influenced the production and transport of FT and the transition to flowering.…”

“…Swapping Region 2 of FT (L28-G98) into TSF imbued it with better florigenic activity and chimeric proteins were detectable in the shoot apex. However, insertion of TSF Region 2 into FT did not block FT movement, indicating the influence of other FT regions.Turning to other regulators of FT movement, the Arabidopsis genes FTIP1 and FE both promote flowering in long days and are expressed in the phloem [41,42 ]. Less FT protein was present in the shoot apex of ftip1 mutant plants because of a reduction in the amount of FT protein entering the sieve elements from the phloem companion cells, while single-leaf induction of FT protein, saw fe mutants accumulating less FT protein in their shoot apices than wild type plants.…”