Plant Molecular Biology 49: 339–348, 2002.
Perrot-Rechenmann and Hagen (Eds.), Auxin Molecular Biology.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
A short history of auxin-binding proteins
Richard M. Napier
, Karine M. David
and Catherine Perrot-Rechenmann
Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, UK;
Institut des Sciences du V´eg´etal,
CNRS, Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France (
author for correspondence; e-mail
Received 31 August 2001; accepted in revised form 16 October 2001
Key words: auxin-binding, chromotography, photolabelling
Plant hormone receptors have proved to be elusive re-
search targets. The successes of describing receptors
from animals and bacteria have not yet been matched
for plants. Nevertheless, where candidate receptors
have been identiﬁed, they have been subjected to de-
tailed examination. One such is the protein known as
ABP1, an auxin-binding protein ﬁrst described from
maize (Zea mais L.).
The ﬁrst detection of ABP1 was as an auxin-
binding activity in crude membrane preparations of
etiolated coleoptiles (Hertel et al., 1972). Over the
next decade this binding activity was characterized in
detail for ligand speciﬁcity (Ray et al., 1977), afﬁnity
(Ray, 1977a; Batt et al., 1976) and cellular com-
partmentalization (Ray et al., 1977). In 1985, the
binding protein was puriﬁed for the ﬁrst time (Löbler
and Klämbt, 1985) leading on to functional studies of
ABP1, examination of its cell biology and its structure.
This review summarizes the advances made in each of
It would be incorrect to suggest that all auxin binding
in plants could be ascribed to ABP1. There have been
numerous reports of other binding sites for indole-3-
acetic acid. Most have been discovered through the
use of tritiated azido IAA, a photoactive auxin ana-
logue (Melhado et al., 1982). A number of labelled
proteins from a range of plants have been traced and
sequenced, almost all turning out to be enzymes (Venis
and Napier, 1995).
Maize ABP1 is on the list of photolabelled pro-
teins and we will return to the activities of this below.
For the remainder, the interaction with auxin at phys-
iologically relevant concentrations has failed to alter
the protein’s activity. As such, the binding fails to
satisfy one of the key criteria of receptors, namely
that ligand binding initiates a biologically relevant
response. Although these proteins are not likely to
be receptors, this certainly does not mean that they
are not relevant to auxin biochemistry or physiol-
ogy. Indeed, photolabelling has identiﬁed conjugate
hydrolases, glutathione S-transferases and, possibly,
components of the auxin transport machinery (Venis
and Napier, 1995).
Auxin afﬁnity chromatography
Afﬁnity puriﬁcation has added a number of new auxin-
binding proteins to the list recently. A phenylacetic
acid column is often used to purify maize ABP1,
but it has also been shown to select for a 44 kDa
protein from pea (Reinard et al., 1998). Further char-
acterisation revealed that this protein is an isovaleryl-
CoA dehydrogenase, an enzyme necessary for leucine
catabolism in mammals and targeted to mitochondria
(Reinard et al., 2000).
A number of soluble auxin-binding proteins have
been reported by Sakai’s group (Sugaya and Sakai,
1996). Their 2,4-D matrix has been shown to purify a
glutathione-dependent formaldehyde dehydrogenase.
A 2,4-D matrix was also used to purify peach auxin-
binding proteins (Ohmiya et al., 1993), later shown
to be members of the protein superfamily known as
the germins (Dunwell et al., 2000). It is interesting to
note that ABP1 is also a member of this superfamily,