Plant Molecular Biology 39: 539–549, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Regulation by biotic and abiotic stress of a wheat germin gene encoding
oxalate oxidase, a H
Anne Berna and François Bernier
Institut deBiologie Mol´eculairedes Plantes,Institutde Botanique,28rue Goethe,67083StrasbourgCedex, France
author for correspondence)
Received 17 February 1998; accepted in revised form 22 September 1998
Key words: cadmium, copper, germin, oxalate oxidase, stress response, tobacco mosaic virus
Germins and germin-like proteins (GLPs) constitute a ubiquitous family of plant proteins that seem to be involved
in many developmentaland stress-related processes. Wheat germin has been extensively studied at the biochemical
level: it is found in the apoplast and the cytoplasm of germinating embryo cells and it has oxalate oxidase activity
(EC 188.8.131.52). Germin synthesis can also be induced in adult wheat leaves by auxins and by a fungal pathogen but
it remains to be determined whether the same gene is involved in developmental, hormonal and stress response. In
this work, we have studied the expression of one of the wheat germin genes, named gf-2.8, in wheat as well
as in transgenic tobacco plants transformed with either this intact gene or constructs with GUS driven by its
promoter. This has allowed us to demonstrate that expression of this single gene is both developmentally and
pathogen-regulated. In addition, we show that expression of the wheat gf-2.8 germin gene is also stimulated by
some abiotic stresses, especially the heavy metal ions Cd
. Several chemicals involved in stress
signal transduction pathways were also tested: only polyamines were shown to stimulate expression of this gene.
Because regulation of the wheat gf-2.8 germin gene is complex and because its product results in developmental
and stress-related release of hydrogen peroxide in the apoplast, it is likely that it plays an important role in several
aspects of plant growth and defence mechanisms.
Germin is a protein which was ﬁrst found to be specif-
ically associated with germination of wheat (Triticum
aestivum) seeds . It was later discovered that there
are several germin isoforms and genes in wheat and
that they are not all involved in germination .
Furthermore, it has become obvious in recent years
that germins are not speciﬁc to germination and are
not restricted to cereals as originally thought. In fact,
germin-like proteins (GLPs) or coding elements have
now been found in several Angiosperms (Hordeum
vulgare, Oryza sativa, Saccharum ofﬁcinale, Phar-
bitis nil, Mesembryanthemum crystallinum, Prunus
persica, Pisum sativum, Fragaria ananassa, Sinapis
alba, Brassica napus and Arabidopsis thaliana), in
in a Myxomycete (Physarum polycephalum) [5, 8, 9,
11, 18, 19, 32–34, 36].
It is now known that germins and germin-like pro-
teins are part of a superfamily of proteins together
with seed storage globulins and sucrose-binding pro-
teins [2, 6]. In fact, perfect conservation of many
key residues has allowed the use of known vicilin
three-dimensional structures for computer modelling
of germin . Two recent studies have demonstrated
that all these proteins are part of an even larger su-
perfamily of proteins all sharing the same predicted
β-barrel core structure . Distant germin relatives
have been identiﬁed in fern spores, in prokaryotes
and in animals [11, 12, 38]. Interestingly, the pu-
tative prokaryotic germin and GLP ancestors appear
to be involved in desiccation tolerance, especially by
contributing to extracellular matrix synthesis .