A Short History of florigen,

1
(No Transcript)
2

• A Short History of florigen,
• - The identity of florigen remains one of the
  major mysteries in plant biology.
• In 1865, Sachs observed that leaves in the light
  produce flower-forming substances, which are
  present in small quantities and lead to the
  formation of flowers.
• The floral stimulus, or florigen, is formed in
  the leaves as a response to an inductive
  photoperiod and translocated through the phloem
  to the apical meristem.
• 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).

3

• What Could Florigen Be?
• - The original assumption was that the phloem
  only transported assimilates in the form of
  carbohydrates.
• Results in recent years have shown that, apart
  from sugars, the phloem contains small molecules,
  peptides and proteins (Fisher et al. 1992 Sakuth
  et al. 1993 Marentes and Grusak 1998
  Xoconostle-Cazares et al. 1999 Kehr et al.
  1999), and nucleic acids (Kühn et al. 1997
  Ruiz-Medrano et al. 1999).
• The contents of the phloem are now known to be
  so complex that phloem transport has been called
  the "superinformation highway" of plants (Lucas
  2000).

4
Mass Sequence Non-flowering Sequence similarities ()
2162 GPPKYXGSASEIA Reduced No similarities found
5075/5167 KAVIVPILANLVLVHypKAAIVPGLVSLIVVPMAAILPDLATQVLPFAVIVEIPFSLRLVP Detected A.t. 2-oxo-glutarate/malate translocator-like protein AF370494 (60)Rice pyrophosphatase ovp1, AB012765 (60)Trillium maturase, AB017379 (60)Phophorylmutases in bacteria
1860 LDVTLGSDDGGLVFIPQNLDVLLGGDDGSLAFIPGNLDVLLGSDDGGLAFVPNN Not determined Potato leaf EST425039, BE921270 (72) with similarity to plastocyanin from, e.g., Mercurialis perennis
3388 VYVHGNFTTGSGHNS Modified Possibly glycosylatedSimilarity to protein kinases
(From Hoffmann-Benning et al., Planta
216140147, 2002)
5
Early Flowering Mutant

• - Arabidopsis is a facultative long-day plant
  long days stimulate the transition to flowering,
  but the plants will eventually flower under short
  day conditions.
• CONSTANS mediates between photoperiod perception
  and the transition to reproductive growth, and
  transcript levels accumulate under inductive,
  long-day conditions (Suarez-Lopez et al., 2001).
• - Arabidopsis plants homozygous for mutant
  alleles of CO flower late under long-day
  conditions, whereas plants overexpressing CO
  flower early (Putterill et al., 1995).

6
(No Transcript)
7

• FLOWERING LOCUS T (FT) is a downstream target of
  CO, and a correlation between FT and CO
  expression patterns argues that CO does not
  directly promote gene expression in cells in
  which CO, itself, is not expressed (Takada and
  Goto, 2003).
• Overexpression of FT in several tissues,
  including phloem-limited expression, results in
  early flowering in Arabidopsis, suggesting that
  FT also acts upstream of florigen (An et al.,
  2004).
• FT, a small protein of 23 kDa, shares homology
  with RAF-kinase-inhibitor proteins in mammals
  (Kardailsky et al., 1999 Kobayashi et al.,
  1999). FT is thus smaller than the green
  fluorescent protein (GFP 26 kDa) which is able
  pass through the plasmodesmata between companion
  cells and sieve elements, and move long-distance
  via the phloem (Imlau et al., 1999).
• If florigen is a macromolecule, then FTs small
  size and potential role in modulating
  phosphorylation make it an intriguing candidate
  for the phloem-mobile floral stimulus.

8

• Researchers at the Umea Plant Science Centre in
  Sweden and the Universite Joseph Fourier in
  France have identified the messenger RNA for the
  flowering locus T (FT) gene as the elusive
  florigen signaling compound, appears to be this
  trigger for initiation of flowering.
• The group constructed transgenic plants
  expressing the FT gene and the marker gene GUS
  under control of a heat-shock inducible promoter
  (Hsp) from soybean as well as the FT promoter
  (pFT). When microdissected plant tissues, whole
  plants or individual leaves were subjected to
  heating, gene expression levels could be
  monitored throughout the plants.
• In this way they were able to follow expression
  levels of FT in various tissues and confirm
  movement of the FT-induced signal from leaf to
  apex tissues.
• - Huang, T., Bohlenius, H., Eriksson, S., Parcy,
  F., Nilsson, O., (2005) The mRNA of the
  Arabidopsis Gene FT Moves front Leaf to Shoot
  Apex and Induces Flowering Science 309(5741)
• - Abe, M. Kobayashi, Y., Yamamoto, S., Daimon,
  Y., Yamaguchi, A., Ikeda, Y., Ichinoki, H.,
  Notaguchi, M., Goto, K., Araki, T.., (2005) FD,
  a bZIP Protein Mediating Signals from the Floral
  Pathway Integrator FT at the Shoot Apex Science,
  309(5737) 1052-1056.
• - Wigge, P.A., Kim, M.C., Jaeger, K.E., Busch,
  W., Markus Schmid, M., Lohmann, J.U., Weigel, D.,
  (2005) Integration of Spatial and Temporal
  Information During Floral Induction in
  Arabidopsis Science 309(5737) 1056-1059.
• - Hoffmann-Benning, S., Zeevaart, J.A.D.
  Searching for Florigen Plant Physiology Online
  242 (2003) http//www.plantphys.net/article.php?c
  heid288
• - Ayre, B.G., Florigen and a Genetic Approach to
  Long-Distance Signaling Through the Phloem Plant
  Physiology Online 243 (2005) http//www.plantphys
  .net/article.php?cheid291
• - Miguel A. Blázquez (2005) The Right Time and
  Place for Making Flowers Science 309 (5737)
  1024-1025.
•  

Plant Florigen factor identified.
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)