Plant Molecular Biology 51: 341–349, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
Characterization of the expression of Phaseolus vulgaris OCT1,a
dehydration-regulated gene that encodes a new type of phloem transporter
Gisele A.M. Torres, Christine Lelandais-Bri
ere, Evelyne Besin, Marie-France Jubier, Odile
Roche, Christelle Mazubert, Fabienne Corre-Menguy and Caroline Hartmann
Institut de Biotechnologie des Plantes, Universit´e Paris-Sud, UMR CNRS 8618, 91405 Orsay Cedex, France.
author for correspondence; e-mail firstname.lastname@example.org).
Received 31 October 2001; accepted in ﬁnal form 15 June 2002
Key words: common bean, drought-regulated gene, organic cation transporter, phloem carrier, water stress
A cDNA coding for a putative organic cation transporter (OCT) was isolated from Phaseolus vulgaris roots by
differential display RT-PCR and the corresponding full-length cDNA (named PvOCT1) was subsequently obtained
by RACE-PCR. Hydropathy proﬁles of the deduced amino acid sequence (547 residues) predicted the existence of
twelve membrane–spanning domains, which are highly conserved in the major facilitator superfamily (MFS). Three
speciﬁc domains, which characterize organic ion transporters in animals, can also be observed in the predicted
protein. In the non-stressed plants, northern analysis showed that PvOCT1 is strongly expressed in roots and stems,
while in situ hybridization revealed the presence of PvOCT1 transcripts in phloem cells. In roots PvOCT1 transcript
levels transitorily increased after one hour of dehydration and then dramatically decreased. This decrease was
associated with enhanced abundance of PvNCED1 mRNA encoding the enzyme thought to catalyze the limiting
step of abscisic acid biosynthesis.
Plant growth requires coordination of the activities of
two spatially distant but interdependent regions: aerial
shoots that harvest light and CO
, and subterranean
roots that take up water and mineral nutrients. For this
purpose, xylem carries water and mineral compounds
from roots to leaves whereas phloem tissue is special-
ized in long distance transport from sites of assimilates
production to sites of utilization. Moreover, the side-
by-side arrangement of xylem and phloem throughout
the plant provides opportunity for solute exchange be-
tween the two vascular tissues. During the last decade,
considerable research has been devoted toward un-
derstanding the role(s) of phloem in the distribution
of compounds such as photoassimilates, proteins and
RNA. This vascular tissue is now considered as an
The nucleotide sequence data reported will appear in the Gen-
Bank Nucleotide Sequence Databases under the accession number
information superhighway through which solutes, sig-
naling molecules and a wide range of macromolecules
ﬂow from one part of the plant to another (Oparka and
Santa Cruz, 2000).
It is clear that phloem loading and unloading
are carried out, at least in part, by active transport.
Transporters involved in phloem loading of sucrose
(Lemoine, 2000) and amino acids (Delrot et al., 2000)
have been extensively characterized in several species,
and it appears that loading mechanisms differ among
plant species (Schulz, 1998). For these molecules, it
has been demonstrated that phloem loading always oc-
curs at the surface of a restricted number of cell types
localized at the small sieve elements in minor veins
(Fischer et al., 1998).
Several physiological data suggest that long dis-
tance transport via the phloem is controlled by devel-
opmental and environmental conditions (Delrot et al.,
2000). For example, in response to cold, water or
salt stress, plants accumulate compatible osmolytes