The indolic compound auxin regulates virtually every aspect of plant growth and development, but its role in embryogenesis and its molecular mechanism of action are not understood. We describe two mutants of Arabidopsis that define a novel gene called AUXIN-RESISTANT6 (AXR6) which maps to chromosome 4. Embryonic development of the homozygous axr6 mutants is disrupted by aberrant patterns of cell division, leading to defects in the cells of the suspensor, root and hypocotyl precursors, and provasculature. The homozygous axr6 mutants arrest growth soon after germination lacking a root and hypocotyl and with severe vascular pattern defects in their cotyledons. Whereas previously described mutants with similar developmental defects are completely recessive, axr6 heterozygotes display a variety of morphological and physiological alterations that are most consistent with a defect in auxin physiology or response. The AXR6 gene is likely to be important for auxin response throughout the plant, including early development.

REFERENCES

Abel
S.
,
Theologis
A.
(
1996
)
Early genes and auxin action.
Plant Physiol
111
,
9
17
Abel
S.
,
Nguyen
M. D.
,
Theologis
A.
(
1995
)
The PS-IAA4/5-like family of early auxin-inducible mRNAs in Arabidopsis thaliana.
J. Mol. Biol
251
,
533
549
Abel
S.
,
Oeller
P. W.
,
Theologis
A.
(
1994
)
Early auxin-induced genes encode short-lived nuclear proteins.
Proc. Natl. Acad. Sci. USA
91
,
326
330
Berleth
T.
,
Jurgens
G.
(
1993
)
The role of the monopteros gene in organising the basal body region of the Arabidopsis embryo.
Development
118
,
575
587
Boerjan
W.
,
Cervera
M. T.
,
Delarue
M.
,
Beeckman
T.
,
Dewitte
W.
,
Bellini
C.
,
Caboche
M.
,
Van Onckelen
H.
,
Van Montagu
M.
,
Inze
D.
(
1995
)
Superroot, a recessive mutation in Arabidopsis, confers auxin overproduction.
Plant Cell
7
,
1405
1419
Chen
R.
,
Rosen
E.
,
Masson
P. H.
(
1999
)
Gravitropism in higher plants.
Plant Physiol
120
,
343
350
del Pozo
J. C.
,
Timpte
C.
,
Tan
S.
,
Callis
J.
,
Estelle
M.
(
1998
)
The ubiquitin-related protein RUB1 and auxin response in Arabidopsis.
Science
280
,
1760
1763
Fabri
C. O.
,
Schäffner
A. R.
(
1994
)
An Arabidopsis thaliana RFLP mapping set to localize mutations to chromosomal regions.
Plant J
5
,
149
156
Fischer
C.
,
Neuhaus
G.
(
1996
)
Influence of auxin on the establishment of bilateral symmetry in monocots.
Plant J
9
,
659
669
Fisher
R. H.
,
Barton
M. K.
,
Cohen
J. D.
,
Cooke
T. J.
(
1996
)
Hormonal studies of fass, an Arabidopsis mutant that is altered in organ elongation.
Plant Physiol
110
,
1109
1121
Guzman
P.
,
Ecker
J. R.
(
1990
)
Exploiting the triple response of Arabidopsis to identify ethylene-related mutants.
Plant Cell
2
,
512
523
Hadfi
K.
,
Speth
V.
,
Neuhaus
G.
(
1998
)
Auxin-induced developmental patterns in Brassica juncea embryos.
Development
125
,
879
887
Hamann
T.
,
Mayer
U.
,
Jurgens
G.
(
1999
)
The auxin-insensitive bodenlos mutation affects primary root formation and apical-basal patterning in the Arabidopsis embryo.
Development
126
,
1387
1395
Hardtke
C. S.
,
Berleth
T.
(
1998
)
The Arabidopsis gene MONOPTEROS encodes a transcription factor mediating embryo axis formation and vascular development.
EMBO J
17
,
1405
1411
Hobbie
L.
,
Estelle
M.
(
1995
)
The axr4 auxin-resistant mutants of Arabidopsis thaliana define a gene important for root gravitropism and lateral root initiation.
Plant J
7
,
211
220
Jones
A. M.
,
Im
K. H.
,
Savka
M. A.
,
Wu
M. J.
,
DeWitt
N. G.
,
Shillito
R.
,
Binns
A. N.
(
1998
)
Auxin-dependent cell expansion mediated by overexpressed auxin-binding protein 1.
Science
282
,
1114
1117
Kovtun
Y.
,
Chiu
W. L.
,
Zeng
W.
,
Sheen
J.
(
1998
)
Suppression of auxin signal transduction by a MAPK cascade in higher plants.
Nature
395
,
716
720
Laux
T.
,
Jurgens
G.
(
1997
)
Embryogenesis: a new start in life.
Plant Cell
9
,
989
1000
Leyser
H. M.
,
Lincoln
C. A.
,
Timpte
C.
,
Lammer
D.
,
Turner
J.
,
Estelle
M.
(
1993
)
Arabidopsis auxin-resistance gene AXR1 encodes a protein related to ubiquitin-activating enzyme E1.
Nature
364
,
161
164
Leyser
H. M.
,
Pickett
F. B.
,
Dharmasiri
S.
,
Estelle
M.
(
1996
)
Mutations in the AXR3 gene of Arabidopsis result in altered auxin response including ectopic expression from the SAUR-AC1 promoter.
Plant J
10
,
403
413
Lincoln
C.
,
Britton
J. H.
,
Estelle
M.
(
1990
)
Growth and development of the axr1 mutants of Arabidopsis.
Plant Cell
2
,
1071
1080
Liu
C.-M.
,
Xu
Z.-H.
,
Chua
N.-H.
(
1993
)
Auxin polar transport is essential for the establishment of bilateral symmetry during early plant embryogenesis.
Plant Cell
5
,
621
630
Maher
E. P.
,
Martindale
S. J.
(
1980
)
Mutants of Arabidopsis thaliana with altered responses to auxins and gravity.
Biochem. Genet
18
,
1041
1053
Masucci
J. D.
,
Schiefelbein
J. W.
(
1996
)
Hormones act downstream of TTG and GL2 to promote root hair outgrowth during epidermis development in the Arabidopsis root.
Plant Cell
8
,
1505
1517
Mizoguchi
T.
,
Gotoh
Y.
,
Nishida
E.
,
Yamaguchi-Shinozaki
K.
,
Hayashida
N.
,
Iwasaki
T.
,
Kamada
H.
,
Shinozaki
K.
(
1994
)
Characterization of two cDNAs that encode MAP kinase homologues in Arabidopsis thaliana and analysis of the possible role of auxin in activating such kinase activities in cultured cells.
Plant J
5
,
111
122
Oono
Y.
,
Chen
Q. G.
,
Overvoorde
P. J.
,
Kohler
C.
,
Theologis
A.
(
1998
)
age mutants of Arabidopsis exhibit altered auxin-regulated gene expression.
Plant Cell
10
,
1649
1662
Pickett
F. B.
,
Wilson
A. K.
,
Estelle
M.
(
1990
)
The aux1 mutation of Arabidopsis confers both auxin and ethylene resistance.
Plant Physiol
94
,
1462
1466
Przemeck
G. K.
,
Mattsson
J.
,
Hardtke
C. S.
,
Sung
Z. R.
,
Berleth
T.
(
1996
)
Studies on the role of the Arabidopsis gene MONOPTEROS in vascular development and plant cell axialization.
Planta
200
,
229
237
Rouse
D.
,
Mackay
P.
,
Stirnberg
P.
,
Estelle
M.
,
Leyser
O.
(
1998
)
Changes in auxin response from mutations in an AUX/IAA gene.
Science
279
,
1371
1373
Ruegger
M.
,
Dewey
E.
,
Gray
W. M.
,
Hobbie
L.
,
Turner
J.
,
Estelle
M.
(
1998
)
The TIR1 protein of Arabidopsis functions in auxin response and is related to human SKP2 and yeast grr1p.
Genes Dev
12
,
198
207
Scheres
B.
,
Wolkenfelt
H.
,
Willemsen
V.
,
Terlou
M.
,
Lawson
E.
,
Dean
C.
,
Weisbeek
P.
(
1994
)
Embryonic origin of the Arabidopsis primary root and root meristem initials.
Development
120
,
2475
2487
Schiavone
F. M.
,
Cooke
T. J.
(
1987
)
Unusual patterns of somatic embryogenesis in the domesticated carrot: developmental effects of exogenous auxins and auxin transport inhibitors.
Cell Differ
21
,
53
62
Smith
L. G.
,
Hake
S.
,
Sylvester
A. W.
(
1996
)
The tangled-1 mutation alters cell division orientations throughout maize leaf development without altering leaf shape.
Development
122
,
481
489
Tena
G.
,
Renaudin
J. P.
(
1998
)
Cytosolic acidification but not auxin at physiological concentration is an activator of MAP kinases in tobacco cells.
Plant J
16
,
173
182
Tian
Q.
,
Reed
J. W.
(
1999
)
Control of auxin-regulated root development by the Arabidopsis thaliana SHY2/IAA3 gene.
Development
126
,
711
721
Timpte
C.
,
Wilson
A. K.
,
Estelle
M.
(
1994
)
The axr2-1 mutation of Arabidopsis thaliana is a gain-of-function mutation that disrupts an early step in auxin response.
Genetics
138
,
1239
1249
Torres-Ruiz
R. A.
,
Jurgens
G.
(
1993
)
Mutations in the FASS gene uncouple pattern formation and embryogenesis in Arabidopsis development.
Development
120
,
2967
2978
Traas
J.
,
Bellini
C.
,
Nacry
P.
,
Kronenberger
J.
,
Bouchez
D.
,
Caboche
M.
(
1995
)
Normal differentiation patterns in plants lacking microtubular preprophase bands.
Nature
375
,
676
677
Uggla
C.
,
Mellerowica
E. J.
,
Sundberg
B.
(
1998
)
Indole-3-acetic acid controls cambial growth in Scots pine by positional signaling.
Plant Physiol
117
,
113
121
Ulmasov
T.
,
Hagen
G.
,
Guilfoyle
T. J.
(
1999
)
Activation and repression of transcription by auxin-response factors.
Proc. Natl. Acad. Sci. USA
96
,
5844
5849
Wilson
A. K.
,
Pickett
F. B.
,
Turner
J. C.
,
Estelle
M.
(
1990
)
A dominant mutation in Arabidopsis confers resistance to auxin, ethylene and abscisic acid.
Mol. Gen. Genet
222
,
377
383
This content is only available via PDF.