Plant Molecular Biology 50: 415–425, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
OsARF1, an auxin response factor from rice, is auxin-regulated and
classiﬁes as a primary auxin responsive gene
, Masaki Furuya
and Peter Nick
Institut für Biologie II, Albert-Ludwigs-Universität, Schänzlestrasse 1, 79104 Freiburg;
Hitachi Advanced Re-
search Laboratory, Hatoyama, Saitama 350-0395;
Present address: Nara Institute of Science and Technology,
8916-5 Takayama, Ikoma, Nara 630-0101, Japan (
author for correspondence; e-mail email@example.com)
Received 18 October 2001; accepted in revised form 15 February 2002
Key words: auxin, auxin response factor (ARF), differential display, Oryza sativa, plant growth
We screened for auxin-induced genes with an expression correlated to the auxin-induced growth response from
rice coleoptiles by ﬂuorescent differential display. A rice homologue of the auxin response factor (ARF) family of
transcriptional regulators, OsARF1, was identiﬁed. An OsARF1:GFP fusion protein was localized to the nucleus.
Steady-state levels of OsARF1 mRNA correlated positively with auxin-dependent differential growth: gravitropic
stimulation enhanced the amount of OsARF1 transcript in the lower, faster-growing ﬂank accompanied by a
decrease in the upper ﬂank of gravitropically stimulated rice coleoptiles. Exogenous auxin up-regulated the steady-
state level of OsARF1 mRNA within 15–30 min. This up-regulation is independent of de novo protein synthesis.
Thus, OsARF1 is the ﬁrst ARF that classiﬁes as an early auxin-responsive gene. The observed auxin-dependent
regulation comprises a new level of regulation in auxin-induced gene expression and is discussed as a possible
feedback mechanism in plant growth control.
Plants survive because they are able to sense environ-
mental conditions and react appropriately by growth
and differentiation. Environmental cues such as light
and gravity trigger a differential growth response, of-
ten resulting in the modiﬁcation of morphology. Early
studies on gravitropism revealed that the perception of
the gravitropic stimulus and the resulting growth reac-
tion are spatially separated (Darwin 1880). The search
for the transmitting signal led to the discovery of the
ﬁrst plant hormone, auxin, characterized in graminean
coleoptiles (Went, 1929). Later the gravitropic and
phototropic reactions of the coleoptile were explained
by the Cholodny-Went theory in terms of a lateral re-
distribution of the basipetal auxin ﬂow, resulting in an
A partial rice cDNA (accession no AB071300) corresponding
to the genomic sequence BAA92916.1 (referred to as ‘OsARF2’
in this study) has been isolated recently and designated OsARF16
(Sato Y et al., 2001). Auxin response factor family in rice. Genes
Genet. 76: 373–380.
auxin concentration gradient that causes the observed
difference in growth (Cholodny, 1927; Went, 1929).
What are the molecular events linking increased
auxin concentrations with the elevated growth of plant
tissues? Numerous genes, such as the SAUR (Mc-
Clure et al., 1989), GH3 (Hagen et al., 1984) and
Aux/IAA (Theologis et al., 1985) genes, are rapidly
and speciﬁcally induced by auxin. Several members
of these gene families are primary auxin-responsive
genes, since their induction is rapid and does not
require de novo protein synthesis (Theologis et al.,
1985; McClure et al., 1987; Abel and Theologis,
1996; Reed, 2001). Auxin responsiveness is conferred
to several of these genes by conserved promotor ele-
ments, termed ‘auxin-responsive elements’ (AuxRE)
(Ulmasov et al., 1995).
AuxRE promotor elements are bound by a new
class of plant-speciﬁc transcription factors, auxin re-
sponse factors (ARFs), identiﬁed in Arabidopsis (Ul-
masov et al., 1997a). ARFs consist of an amino-
terminal DNA-binding domain and most ARFs con-