More than twenty genes are required for the correct initiation, spacing, and morphogenesis of trichomes in Arabidopsis. The initial selection of trichome precursors requires the activity of both the GLABROUS1 (GL1) and TRANSPARENT TESTA GLABROUS (TTG) genes. The GLABRA2 (GL2) gene is required for subsequent phases of trichome morphogenesis such as cell expansion, branching, and maturation of the trichome cell wall. Previous studies have shown that GL2 is a member of the homeodomain class of transcription factors. Here we report a detailed analysis of GL2 expression in the shoot using anti-GL2 antibodies and the GUS reporter gene fused to the GL2 promoter. The GL2 expression profile in the shoot is complex, and involves spatial and temporal variation in developing leaves and trichomes. Two separate promoter domains that are expressed in trichomes were identified. GL2, like GL1, is expressed in developing trichomes and in cells surrounding trichomes during early stages of trichome development. Unlike GL1, GL2 expression persists in mature trichomes. It was found that while GL1 and TTG were not required for the initiation of GL2 expression in the non-trichome cells, the presence of a functional GL1 or TTG gene was able to increase GL2 expression in these cells compared to ttg gl1 plants. The hypothesis that GL1 regulates aspects of GL2 expression is consistent with epistatic analysis of gl1 and gl2 and the expression patterns of GL1 and GL2. In support of this hypothesis, it was found that ectopic expression of GL1 in the presence of ectopic expression of the maize R gene, which can bypass the requirement for TTG, can ectopically activate GL2 transcription.

REFERENCES

Biedenkapp
H.
,
Borgmeyer
U.
,
Sippel
A. E.
,
Klempnauer
K.-H.
(
1988
)
Vital myb oncogene encodes a sequence-specific DNA-binding activity.
Nature
335
,
835
837
Carabelli
M.
,
Sessa
G.
,
Baima
S.
,
Morelli
G.
,
Ruberti
I.
(
1993
)
The Arabidopsis Athb-2 and-4 genes are strongly induced by far-red-rich light.
Plant J
4
,
469
479
Di Cristina
M.
,
Sessa
G.
,
Dolan
L.
,
Linstead
P.
,
Baima
S.
,
Ruberti
I.
,
Morelli
G.
(
1996
)
The Arabidopsis Athb-10 (GLABRA2) is an HD-Zip protein required for regulation of root hair development.
Plant J
10
,
393
402
Evan
G. I.
,
Lewis
G.
,
Ramsay
G.
,
Bishop
J.
(
1985
)
Isolation of monoclonal antibodies specific for human c-myc proto-oncogene product.
Mol. Cell. Biol
5
,
3610
3616
Galway
M. E.
,
Masucci
J. D.
,
Lloyd
A. M.
,
Walbot
V.
,
Davis
R. W.
,
Schiefelbein
J. W.
(
1994
)
The TTG gene is required to specify epidermal cell fate and cell patterning in the Arabidopsis root.
Dev. Biol
166
,
740
754
Gehring
W.
,
Affolter
M.
,
Burglin
T.
(
1994
)
Homeodomain proteins.
Ann. Rev. Biochem
63
,
487
526
Grotewold
E.
,
Drummond
B. J.
,
Bowen
B.
,
Peterson
T.
(
1994
)
The myb -homologous P gene controls phlobaphene pigmentation in maize floral organs by directly activating a flavonoid biosynthetic gene subset.
Cell
76
,
543
553
Hulskamp
M.
,
Misera
S.
,
Jurgens
G.
(
1994
)
Genetic dissection of trichome cell development in Arabidopsis.
Cell
76
,
555
566
Jefferson
R. A.
(
1987
)
Assaying chimeric gene in plants: The GUS gene fusion system.
Plant Mol. Biol
5
,
387
405
Kerstetter
R.
,
Vollbrecht
E.
,
Lowe
B.
,
Veit
B.
,
Yamaguchi
J.
,
Hake
S.
(
1994
)
Sequence analysis and expression patterns divide the maize knotted1-like homeobox genes into two classes.
Plant Cell
6
,
1877
1887
Kessel
M.
,
Gruss
P.
(
1990
)
Murine development control genes.
Science
249
,
374
379
Koornneef
M.
,
Dellaert
S. W. M.
,
van der Veen
J. H.
(
1982
)
EMS-and radiation-induced mutation frequencies at individual loci in Arabidopsis thaliana (L) Heynh.
Mutat. Res
93
,
109
123
Larkin
J. C.
,
Oppenheimer
D. G.
,
Lloyd
A.
,
Paparozzi
E. T.
,
Marks
M. D.
(
1994
)
The roles of GLABROUS1 and TRANSPARENT TESTA GLABRA genes in Arabidopsis trichome development.
Plant Cell
6
,
1065
1076
Larkin
J. C.
,
Oppenheimer
D. G.
,
Pollock
S.
,
Marks
M. D.
(
1993
)
Arabidopsis GLABROUS1 gene requires downstream sequences for function.
Plant Cell
5
,
1739
1748
Li
S.
,
Santini
J.
,
Nicolaou
O.
,
Parish
R.
(
1996
)
A novel myb-related gene from Arabidopsis thaliana.
FEBS Letters
379
,
117
121
Lincoln
C.
,
Long
J.
,
Yamaguchi
K.
,
Hake
S.
(
1994
)
A knotted1-like homeobox gene in Arabidopsis is expressed in the vegetative meristem and dramatically alters leaf morphology when overexpressed in transgenic plants.
Plant Cell
6
,
1859
1876
Lloyd
A. M.
,
Walbot
V.
,
Davis
R. W.
(
1992
)
Anthocyanin production in dicots activated by maize anthocyanin-specific regulators, R and C1.
Science
258
,
1773
1775
Lloyd
A.
,
Schena
M.
,
Walbot
V.
,
Davis
R.
(
1994
)
Epidermal cell fate determination in Arabidopsis: patterns defined by a steroid-inducible regulator.
Science
266
,
436
439
Lu
P.
,
Porat
R.
,
Nadeau
J.
,
O'Neill
S.
(
1996
)
Identification of a meristem L1 layer-specific gene in Arabidopsis that is expressed during embryonic pattern formation and defines a new class of homeobox genes.
Plant Cell
8
,
2155
2168
Ludwig
S. R.
,
Habera
L. F.
,
Dellaporta
S. L.
,
Wessler
S. R.
(
1989
)
Lc, a member of the maize R gene family responsible for tissue-specific anthocyanin production, encodes a protein similar to transcription factors and contains the Myc homology region.
Proc. Natl. Acad. Sci. USA
86
,
7092
7096
Marks
M. D.
(
1994
)
The making of a plant hair.
Cur. Biol
4
,
621
623
Nadeau
J.
,
Zhang
X.
,
Li
J.
,
O'Neill
S.
(
1996
)
Ovule development: Identification of stage-specific and tissue-specific cDNAs.
Plant Cell
8
,
213
239
Oppenheimer
D. G.
,
Herman
P. L.
,
Esch
J.
,
Sivakumaran
S.
,
Marks
M. D.
(
1991
)
A myb -related gene required for leaf trichome differentiation in Arabidopsis is expressed in stipules.
Cell
67
,
483
493
Quaedvlieg
N.
,
Dock
J.
,
Rook
F.
,
Weisbeek
P.
,
Smeekens
S.
(
1995
)
The homeobox gene ATH1 of Arabidopsis is derepressed in the photomorphogenetic mutants cop1 and det1.
Plant Cell
7
,
117
129
Reiser
L.
,
Modursan
Z.
,
Margossian
L.
,
Samach
A.
,
Ohad
N.
,
Haugh
G.
,
Fischer
R.
(
1995
)
The BELL1 gene encodes a homeodomain protein involved in pattern formation in the Arabidopsis ovule primordium.
Cell
83
,
735
742
Rerie
W. G.
,
Feldmann
K. A.
,
Marks
M. D.
(
1994
)
The GLABRA2 gene encodes a homeo domain protein required for normal trichome development in Arabidopsis.
Genes Dev
8
,
1388
1399
Ruberti
I.
,
Sessa
G.
,
Lucchetti
S.
,
Morelli
G.
(
1991
)
A novel class of plant proteins containing a homeodomain with a closely linked leucine zipper motif.
EMBO J
10
,
1787
1791
Schena
M.
,
Davis
R.
(
1992
)
HD-Zip proteins: Members of an Arabidopsis homeodomain protein superfamily.
Proc. Natl. Acad. Sci. USA
89
,
3894
3898
Sablowski
R. W. M.
,
Moyano
E.
,
Culianez-Macia
F.A.
,
Schuch
W.
,
Martin
C.
,
Bevan
M.
(
1994
)
A flower-specific myb protein activates transcription of phenylpropanoid biosynthetic genes.
EMBO J
13
,
128
137
Taniguchi
M.
,
Mori
J.
,
Sugiyama
T.
(
1994
).
Structure of genes that encode isozymes of aspartate amimotransferase in Panicum miliaceum L., a C4 plant.
Plant Mol. Biol
26
,
723
734
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