During the initial vegetative phase, the Arabidopsis shoot meristem produces leaves with associated lateral shoots at its flanks, while the later reproductive phase is characterized by the formation of flowers. The LEAFY gene is an important element of the transition from the vegetative to the reproductive phase, as LEAFY is both necessary and sufficient for the initiation of individual flowers. We have analyzed in detail the expression of LEAFY during the plant life cycle, and found that LEAFY is extensively expressed during the vegetative phase. In long days, Arabidopsis plants flower soon after germination, and this is paralleled by rapid upregulation of LEAFY. In short days, Arabidopsis plants flower several weeks later than in long days, but LEAFY expression increases gradually before flowering commences. Application of the plant hormone gibberellin, which hastens flowering in short days, enhances the gradual change in LEAFY expression observed in short days. Changes in LEAFY expression before the transition to flowering suggest that the time point of this transition is at least partly controlled by the levels of LEAFY activity that are prevalent at a given time of the life cycle. This assumption is borne out by the finding that increasing the copy number of endogenous LEAFY reduces the number of leaves produced before the first flower is formed. Thus, LEAFY combines properties of flowering-time and flower-meristem-identity genes, indicating that LEAFY is a direct link between the global process of floral induction and the regional events associated with the initiation of individual flowers.

REFERENCES

Alvarez
J.
,
Guli
C. L.
,
Yu
X.-H.
,
Smyth
D. R.
(
1992
)
terminal flower: a gene affecting inflorescence development in Arabidopsis thaliana.
Plant J
2
,
103
116
Bechtold
N.
,
Ellis
J.
,
Pelletier
G.
(
1993
)
In planta Agrobacterium mediated gene transfer by infiltration of adult Arabidopsis thaliana plants.
C. R. Acad. Sci
316
,
1194
1199
Bradley
D.
,
Carpenter
R.
,
Copsey
L.
,
Vincent
C.
,
Rothstein
S.
,
Coen
E.
(
1996
)
Control of inflorescence architecture in Antirrhinum.
Nature
379
,
791
797
Bradley
D.
,
Vincent
C.
,
Carpenter
R.
,
Coen
E.
(
1996
)
Pathways for inflorescence and floral induction in Antirrhinum.
Development
122
,
1535
1544
Bradley
D. J.
,
Ratcliffe
O. J.
,
Vincent
C.
,
Carpenter
R.
,
Coen
E. S.
(
1997
)
Inflorescence commitment and architecture in Arabidopsis.
Science
275
,
80
83
Chien
J. C.
,
Sussex
I. M.
(
1996
).
Differential regulation of trichome formation on the adaxial and abaxial leaf surfaces by gibberellins and photoperiod in Arabidopsis thaliana (L.) Heynh.
Plant Physiol
111
,
1321
8
Coen
E. S.
,
Romero
J. M.
,
Doyle
S.
,
Elliot
R.
,
Murphy
G.
,
Carpenter
R.
(
1990
)
floricaula: a homeotic gene required for flower development in Antirrhinum majus.
Cell
63
,
1311
1322
Corbesier
L.
,
Gadisseur
I.
,
Silvestre
G.
,
Jacqmard
A.
,
Bernier
G.
(
1996
)
Design in Arabidopsis thaliana of a synchronous system of floral induction by one long day.
Plant J
9
,
947
952
Drews
G. N.
,
Bowman
J. L.
,
Meyerowitz
E. M.
(
1991
)
Negative regulation of the Arabidopsis homeotic gene AGAMOUS by the APETALA2 product.
Cell
65
,
991
1002
Hempel
F. D.
,
Feldman
L. J.
(
1994
)
Bi-directional inflorescence development in Arabidopsis thaliana: Acropetal initiation of flowers and basipetal initiation of paraclades.
Planta
192
,
276
286
Hempel
F. D.
,
Feldman
L. J.
(
1995
)
Specification of chimeric flowering shoots in wild-type Arabidopsis.
Plant J
8
,
725
731
Huala
E.
,
Sussex
I. M.
(
1992
)
LEAFY interacts with floral homeotic genes to regulate Arabidopsis floral development.
Plant Cell
4
,
901
913
Ingram
G. C.
,
Goodrich
J.
,
Wilkinson
M. D.
,
Simon
R.
,
Haughn
G. W.
,
Coen
E. S.
(
1995
)
Parallels between UNUSUAL FLORAL ORGANS and FIMBRIATA, genes controlling flower development in Arabidopsis and Antirrhinum.
Plant Cell
7
,
1501
1510
Jefferson
R. A.
,
Kavanagh
T. A.
,
Bevan
M. W.
(
1987
)
GUS fusions:- glucuronidase as a sensitive and versatile gene fusion marker in higher plants.
EMBO J
6
,
3901
3907
Jofuku
K. D.
,
den Boer
B. G. W.
,
Van Montagu
M.
,
Okamuro
J. K.
(
1994
)
Control of Arabidopsis flower and seed development by the homeotic gene APETALA2.
Plant Cell
6
,
1211
1225
Kelly
A. J.
,
Bonnlander
M. B.
,
Meeks-Wagner
D. R.
(
1995
)
NFL, the tobacco homolog of FLORICAULA and LEAFY, is transcriptionally expressed in both vegetative and floral meristems.
Plant Cell
7
,
225
234
Kempin
S. A.
,
Savidge
B.
,
Yanofsky
M. F.
(
1995
)
Molecular basis of the cauliflower phenotype in Arabidopsis.
Science
267
,
522
525
Konieczny
A.
,
Ausubel
F. M.
(
1993
)
A procedure for mapping Arabidopsis mutations using co-dominant ecotype-specific PCR-based markers.
Plant J
4
,
403
410
Koornneef
M.
,
Hanhart
C.
,
van Loenen-Martinet
P.
,
Blankestijn de Vries
H.
(
1995
)
The effect of daylength on the transition to flowering in phytochrome-deficient, late-flowering and double mutants of Arabidopsis thaliana.
Physiol. Plant
95
,
260
266
Koornneef
M.
,
Hanhart
C. J.
,
van der Veen
J. H.
(
1991
)
A genetic and physiological analysis of late flowering mutants in Arabidopsis thaliana.
Mol. Gen. Genet
229
,
57
66
Langridge
J.
(
1957
)
Effect of day-length and gibberellic acid on the flowering of Arabidopsis.
Nature
180
,
36
37
Lee
I.
,
Aukerman
M. J.
,
Gore
S. L.
,
Lohman
K. N.
,
Michaels
S. D.
,
Weaver
L. M.
,
John
M. C.
,
Feldmann
K. A.
,
Amasino
R. M.
(
1994
)
Isolation of LUMINIDEPENDENS: a gene involved in the control of flowering time in Arabidopsis.
Plant Cell
6
,
75
83
Lee
I.
,
Wolfe
D. S.
,
Nilsson
O.
,
Weigel
D.
(
1997
)
A LEAFY co-regulator encoded by UNUSUAL FLORAL ORGANS.
Curr. Biol
7
,
95
104
Mandel
M. A.
,
Gustafson-Brown
C.
,
Savidge
B.
,
Yanofsky
M. F.
(
1992
)
Molecular characterization of the Arabidopsis floral homeotic gene APETALA1.
Nature
360
,
273
277
Mandel
M. A.
,
Yanofsky
M. F.
(
1995
)
The Arabidopsis AGL8 MADS box gene is expressed in inflorescence meristems and is negatively regulated by APETALA1.
Plant Cell
7
,
1763
1771
Martínez-Zapater
J. M.
,
Somerville
C. R.
(
1990
)
Effect of light quality and vernalization on late-flowering mutants of Arabidopsis thaliana.
Plant Physiol
92
,
770
776
McBride
K. E.
,
Summerfelt
K. R.
(
1990
)
Improved binary vectors for Agrobacterium -mediated plant transformation.
Plant Mol. Biol
14
,
269
276
Menzel
G.
,
Apel
K.
,
Melzer
S.
(
1996
)
Identification of two MADS box genes that are expressed in the apical meristem of the long-day plant Sinapis alba in transition to flowering.
Plant J
9
,
399
408
Miksche
J. P.
,
Brown
J. A. M.
(
1965
)
Development of vegetative and floral meristems of Arabidopsis thaliana.
Amer. J. Bot
52
,
533
537
Mizukami
Y.
,
Ma
H.
(
1997
)
Determination of Arabidopsis floral meristem identity by AGAMOUS.
Plant Cell
9
,
393
408
Okamuro
J. K.
,
den Boer
B. G. W.
,
Lotys-Prass
C.
,
Szeto
W.
,
Jofuku
K. D.
(
1996
)
Flowers into shoots: photo and hormonal control of a meristem identity switch in Arabidopsis.
Proc. Natl. Acad. Sci. USA
93
,
13831
13836
Poethig
R. S.
(
1990
)
Phase changes and the regulation of shoot morphogenesis in plants.
Science
250
,
923
930
Putterill
J.
,
Robson
F.
,
Lee
K.
,
Simon
R.
,
Coupland
G.
(
1995
)
The CONSTANS gene of Arabidopsis promotes flowering and encodes a protein showing similarities to zinc finger transcription factors.
Cell
80
,
847
857
Schultz
E. A.
,
Haughn
G. W.
(
1991
)
LEAFY, a homeotic gene that regulates inflorescence development in Arabidopsis.
Plant Cell
3
,
771
781
Schultz
E. A.
,
Haughn
G. W.
(
1993
)
Genetic analysis of the floral initiation process (FLIP) in Arabidopsis.
Development
119
,
745
765
Shannon
S.
,
Meeks-Wagner
D. R.
(
1991
)
A mutation in the Arabidopsis TFL1 gene affects inflorescence meristem development.
Plant Cell
3
,
877
892
Simon
R.
,
Igeño
M. I.
,
Coupland
G.
(
1996
)
Activation of floral meristem identity genes in Arabidopsis.
Nature
382
,
59
62
Smyth
D. R.
,
Bowman
J. L.
,
Meyerowitz
E. M.
(
1990
)
Early flower development in Arabidopsis.
Plant Cell
2
,
755
767
Sussex
I. M.
(
1989
)
Developmental programming of the shoot meristem.
Cell
56
,
225
229
Telfer
A.
,
Bollman
K. M.
,
Poethig
R. S.
(
1997
)
Phase change and the regulation of trichome distribution in Arabidopsis thaliana.
Development
124
,
637
644
Weigel
D.
,
Alvarez
J.
,
Smyth
D. R.
,
Yanofsky
M. F.
,
Meyerowitz
E. M.
(
1992
)
LEAFY controls floral meristem identity in Arabidopsis.
Cell
69
,
843
859
Weigel
D.
,
Nilsson
O.
(
1995
)
A developmental switch sufficient for flower initiation in diverse plants.
Nature
377
,
495
500
Wilson
R. N.
,
Heckman
J. W.
,
Somerville
C. R.
(
1992
)
Gibberellin is required for flowering in Arabidopsis thaliana under short days.
Plant Physiol
100
,
403
408
Yang
C.-H.
,
Chen
L.-J.
,
Sung
Z. R.
(
1995
)
Genetic regulation of shoot development in Arabidopsis: role of the EMF genes.
Dev. Biol
169
,
421
435
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