Plant Molecular Biology 52: 1025–1036, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
Molecular characterization and spatial expression of the sunﬂower ABP1
, Denise Meyer, Michel Wolff, Christophe Himber, Malek Alioua and André
Institut de Biologie Mol´eculaire des Plantes CNRS, and Universit´e Louis Pasteur, 12 rue du G´en´eral Zimmer,
67084 Strasbourg Cedex, France (
author for correspondence; e-mail Clement.email@example.com)
Received 24 October 2002; accepted in revised form 27 May 2003
Key words: auxin, auxin-binding protein, in situ hybridization, lateral roots, real-time PCR, sunﬂower
We have used RT-PCR and low-stringency cDNA library screening to isolate the coding sequence of the sunﬂower
auxin-binding protein (ABP1). All the clones analysed contained the same nucleotide sequence, suggesting that
ABP1 is encoded by a single-copy gene in sunﬂower. The deduced amino acid sequence shows a high degree of
similarity with ABP1 proteins from other plant species. Most remarkably, the sunﬂower protein lacks two cysteine
residues present in all other plant ABPs known to date and shown to be involved in a disulﬁde bridge in the
maize protein. Genomic Southern hybridization data support the existence of a single copy of the ABP1 gene in
the sunﬂower genome. Northern hybridization corroborated earlier observations indicating that the steady-state
level of ABP1 transcript is higher in actively dividing and growing organs than in the rest of the plant: it is more
abundant in the shoot apex, ﬂoral buds and immature embryos than in mature leaves, stem, roots and ray ﬂowers.
To characterize the tissular ABP1 transcript distribution in sunﬂower, various organ sections were analysed upon
in situ hybridization. Localized accumulation of the ABP1 transcript suggests that its spatial expression is highly
regulated at the tissue level. In addition, the transcript preferentially accumulates in tissues having a high rate
of cellular division, such as shoot and root apical meristems, leaf primordia and pro-vascular tissues. The ABP1
expression pattern was also studied at a temporal scale during lateral root formation. Real time PCR showed
an elevation of the steady state level of the ABP1 transcript in root axes after 36 h of seed germination. In situ
hybridization revealed that this global increase is the result of local accumulation of the ABP1 transcript in lateral
root primordia, which are known to develop under auxin action. The possibility that a high ABP1 expression level
correlates with a high cellular sensitivity to auxin is discussed.
Abbreviations: ABP1, auxin-binding protein 1; cDNA, complementary DNA; cds, coding DNA sequence
The plant hormone auxin, or indole-3-acetic acid
(IAA), regulates diverse developmental processes in
plants, including apical dominance, embryogenesis,
differentiation of vascular tissues, lateral root form-
ation and tropistic responses (for review see Davies,
1995). At the cellular level, auxin is involved in
cell division, cell elongation and cell differentiation.
Auxin-induced responses result as well from perturb-
ation of the auxin concentration as from the ability
for cells to perceive this perturbation and activate the
subsequent transduction pathway(s). Although tissular
and cellular changes in auxin concentration have been
demonstrated and are still largely studied, the mech-
anism(s) of cellular sensitivity to auxin and its (their)
regulation are not yet clearly established.
Originally puriﬁed from maize (Löbler and
Klämbt, 1985), auxin-binding protein 1 (ABP1) has
been found in many plant species and is the best
characterized candidate for an auxin receptor to date