Florigen concept

2. W.W. Garner and H.A. Allard concluded that day length is a
critical factor for the induction of flowering.
In 1936, Chailakhyan, a Russian plant physiologist, discovered
that changes in day length for floral induction are recognized by
leaves.
He proposed the involvement of a flowering hormone, florigen
produced in leaves, after the stimulus of inductive day length,
and transported to the SAM for floral evocation.
A Short History of florigen

3. MIF, HORT, 2013.
 Later Sachs (1985) also confirmed the presence of florigen in
formation of flowers
Identity of florigen remains one of the major mysteries in plant biology.
Major component of florigen is a protein encoded by the FT gene or its
homologs.
Contd…

5. Florigen: Arabidopsis protein FLOWERING
LOCUS T
 FT is a small, globular protein that exhibits the properties that
would be expected of florigen. Florigen may be a macromolecule
governed by the FLOWERING LOCUS T (FT) gene
 FT protein moves via the phloem from the leaves to the shoot
apical meristem under inductive photoperiods.
 In the meristem, FT forms a complex with the transcription factor
FD to activate floral identity genes
MIF, HORT, 2013.

6.  Grafting experiments (Zeevaart, 1976) have shown that this
floral stimulus is graft transmissible and can be
interchangeable between different species and plants of
different photoperiodic response types (SDP and LDP).
MIF, HORT, 2013.

7. MIF, HORT, 2013.

8. MIF, HORT, 2013.

9.  The Objective of the study
 to determine if the activity of the endogenous FT
gene to promote flowering is transmitted from a
donor scion to a recipient stock
MIF, HORT, 2013.

10. MIF, HORT, 2013.

11.  Detection of transported FT-T7 protein in the
shoot apex of recipient ft-1 stock plants
MIF, HORT, 2013.

12. Conclusion
 FT protein in Arabidopsis and corresponding
proteins in other species part of the mobile
signal that promotes flowering .
 the activity of FT to promote flowering, from the
overexpressing or inducible transgenes or from
the endogenous genes, is transmissible through
a graft junction.
 FT protein is transported from the donor scion
to the apical region of the recipient stock plants
within a short period of 24–28 h
 transport of the FT protein with concomitant
transmission of flowering activity is regulated by
photoperiods
MIF, HORT, 2013.

13. © 2011 Pearson Education, Inc.
flowering
signal
generated
in the leaf
the signal
goes one
way: from
the leaf to
the apex
Grafting
transmittable
13
?
vegetative or
reproductive
growth?
Florigen
Florigen
Florigen
The flowering signal: florigen

14. Notaguchi, M. et al. Plant Cell Physiol. 2008 49:1645-1658;
doi:10.1093/pcp/pcn154
A current model of the action of the FT florigen

15. Interactors of FT and their
functions
 FD gene was isolated from the fd mutant of Arabidopsis Abe, et al.
(2005) and Wigge et al. (2005).
 FD is expressed mainly in the shoot apex Abe, et al. (2005). The
bZIP protein encoded by FD interacts with FT in vitro and in vivo
Abe, et al. (2005).
 FT–FD interaction is essential for FD function because mutations of
the interaction site in FD failed to complement the fd mutant Abe, et
al. (2005)
MIF, HORT, 2013.

16.  14-3-3 proteins have also been identified as FT-interacting proteins.
 A tomato 14-3-3 isoform, 14-3-3/74, was identified by Y2H
interaction with FT and SP, a tomato TFL1 homolog. Overexpression
of 14-3-3 in tomato compensated for the loss of function of the SP
gene Pnueli, L. et al. (2001)
 Most of the FT-interacting proteins have been identified by Y2H
screening. Therefore, their interaction with FT could be mediated by
yeast endogenous proteins
MIF, HORT, 2013.

17. List of FT-interacting proteins
MIF, HORT, 2013.

18. MIF, HORT, 2013.
Nature Vol. 476 August 2011

19. MIF, HORT, 2013.

20.  Fluorescence was detected from:
 Hd3a-mCherry in cytoplasm and
the nucleus.
 from GFP-GF14b in cytoplasm and
weakly in nucleus.
 from CFP-OsFD1 in the nucleus.
MIF, HORT, 2013.

21. Interactions among these three proteins in rice
cells monitored by (BiFC) assays.
MIF, HORT, 2013.
• Hd3a-GF14b interaction was detected in the cytoplasm,
where GF14b was mainly localized.
• Interaction of GF14b with OsFD1, the GF14b-OsFD1 BiFC
signal was mainly detected in the nucleus.
• These results support the hypotheses that the Hd3a-OsFD1
interaction in rice cells is mediated by 14-3-3 and that an
Hd3a-GF14b complex forms in the cytoplasm and then
moves to the nucleus
• Hd3a and GF14b are translocated together from the
cytoplasm to the nucleus, where they form a larger protein
complex with OsFD1

22. Induction of OsMADS15 requires both Hd3a and OsFD1
MIF, HORT, 2013.

23. Conclusion
 binding of 14-3-3 to Hd3a is important for
flowering.
 14-3-3 proteins act as intracellular receptors for
Hd3a (florigen) transported from leaves to the
shoot apex.
 Hd3a enters cells in the shoot apex, it binds 14-
3-3 proteins in the cytoplasm.
 the Hd3a–14-3-3 complex enters the nucleus.
MIF, HORT, 2013.

24.  Newly translated OsFD1 in the cytoplasm
interact with Hd3a–14-3-3 to form the FAC.
 FAC activates transcription of OsMADS15,
leading to floral induction.
 level of OsMADS15 messenger RNA
increased after Hd3a and OsFD1 co-
transformation.
 neither Hd3a nor OsFD1 alone induced
OsMADS15 expression.
MIF, HORT, 2013.

25. MIF, HORT, 2013.

26. MIF, HORT, 2013.

27. MIF, HORT, 2013.

28. MIF, HORT, 2013.

29. MIF, HORT, 2013.

30. MIF, HORT, 2013.

31. MIF, HORT, 2013.

32. MIF, HORT, 2013.