Plant Molecular Biology 40: 355–363, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Expression and cellular localization of Atrab28 during Arabidopsis
, Monique Raynal
, Antonio Borrell
, Fabrice Varoquaux
, Montserrat Pag
and Francisco A. Culi
Departament de Gen`etica Molecular, Centre d’Investigaci´o i Desenvolupament, C.S.I.C., Jordi Girona 18-26,
08034 Barcelona, Spain;
Laboratoire de Physiologie et Biologie Mol´eculaire des Plantes, UMR 5545 CNRS,
Universit´e de Perpignan, 66860 Perpignan, France;
Instituto de Biolog´ıa Molecular y Celular de Plantas, Univer-
sidad Polit´ecnica de Valencia-C.S.I.C., Camino de Vera s/n, 46022 Valencia, Spain (
author for correspondence);
Division of Biology, 156-29, California Institute of Technology, Pasadena, CA 91125, USA;
Division of General Genetics, University of Oslo, P.O. Box 1031, Blindern, 0315 Oslo, Norway
Received 31 July 1998; accepted in revised form 5 February 1999
Key words: Arabidopsis thaliana, embryo-speciﬁc gene expression, Lea proteins
The maize abscisic acid (ABA)-responsive gene rab28 has been shown to be ABA-inducible in embryos and veg-
etative tissues, expression being mostly restricted to vascular elements during late embryogenesis. In the course of
an expressed sequence tags (ESTs) programme, we have isolated an Arabidopsis thaliana gene, Atrab28, encoding
the orthologue of maize rab28.TheAtrab28 cDNA is 1090 bp long, including a poly(A)
stretch, and encodes
a polypeptide of 262 amino acids. Atrab28 antibody against the recombinant protein recognizes a polipeptide
of about 30 kDa and pI 6, in close agreement with the predicted molecular mass and pI. As for maize rab28,
expression studies with Atrab28 revealed high speciﬁcity for embryo tissues, transcription being stimulated by the
transcriptional activator abi3. In contrast, Atrab28 was not induced in vegetative tissues by ABA, osmotic stress or
dehydration. The expression of Atrab28 mRNA and the accumulation of Atrab28 protein was largely restricted to
provascular tissues of mature embryos and in the seed coat outer tegument and embryo and silique epidermis, as
revealed by in situ hybridization and immunocytochemistry with anti-Atrab28 antibodies.
In most plant species a speciﬁc set of proteins accu-
mulate in the seed embryo, during seed maturation,
peaking at seed desiccation (Dure, 1985; Sánchez-
Martínez et al., 1986; Baker et al., 1988; Raynal
et al., 1989). These proteins have been grouped in
several distinct classes and are usually indicated as Lea
(late embryogenesis-abundant) proteins. They also ac-
cumulate in somatic embryos and are considered as
early markers of embryogenic tissues during induc-
The nucleotide sequence data reported will appear in the
EMBL, GenBank and DDBJ Nucleotide Sequence Databases under
the accession number Z27037.
tion of somatic embryogenesis (Baker et al., 1988).
Although the Lea proteins show a different pattern
of expression, they have been shown to be regulated
by the hormone abscisic acid, ABA (Quatrano, 1986;
Galau et al., 1986; Goday et al., 1988; Close et al.,
1989; Giraudat et al., 1994). Accordingly, some of
them have been also named Rab protein, for respon-
sive to ABA (Mundy and Chua, 1988; Pla et al., 1989).
Many Lea proteins are also expressed in vegetative
tissues in response to drought stress (Gómez et al.,
1988; Mundy and Chua, 1988; Delseny et al., 1994).
Though most of these proteins are highly hydrophilic
(Dure et al., 1989) and might be involved in protec-
tion of tissues against extreme dehydration, there is no