Plant Molecular Biology 33: 291–300, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
Cloning and characterization of a pollen-speciﬁc cDNA encoding a
glutamic-acid-rich protein (GARP) from potato Solanum berthaultii
, Ursula Seul and Richard Thompson
uchtungsforschung, Carl-von-Linne Weg 10, D-50829 K
oln, Germany (
Present address: National Laboratory for Agrobiotechnology, Beijing Agricultural University,
100094 Beijing, China
Received 24 November 1994; accepted in revised form 10 October 1996
Key words: glutamic acid-rich protein (GARP), pollen-speciﬁc cDNA, pollen germination, pollen tube growth,
A pollen-speciﬁc cDNA was isolated from a cDNA library of in vitro germinated pollen of the diploid potato
species Solanum berthaultii. The cDNA clone, designated SB401, hybridizesto a messenger RNA of 1.2 kb length
in mature and germinated pollen. SB401 messenger RNA is absent from other parts of the plant, including other
ﬂower tissues. SB401 cDNA, which possesses a long stretch of AT-rich 5
-untranslated leader sequence, encodes
a glutamic acid-rich protein (GARP) which is hydrophilic throughout and contains six imperfect repeated motifs
of the sequence V-V-E-K-K-N/E-E with the di-basic amino acid residue pair (K-K) as the core within the repeats.
These repeats are spaced at irregular intervals and predicted to form an
-helical structure. The SB401 protein was
over-expressed in Escherichia coli and the puriﬁed protein was used for raising antiserum. Both E. coli-expressed
and the endogenous SB401 proteins in pollen and pollen tubes appear much larger on SDS-polyacrylamide gels
than their calculated molecular masses. Immunoblotting revealed the protein to be most abundant in germinated
pollen. The structural features of SB401 protein and a possible role for the protein in pollen development, pollen
germination, and pollen tube growth are discussed.
The male gametophyte of ﬂowering plants, represen-
ted by the pollen grain, has been the subject of intens-
ive investigation [20, 21]. In recent years, the applic-
ation of molecular approaches has revealed more of
the complexity of pollen development, particularly of
is signiﬁcant overlap between gametophytically and
sporophytically expressed genes, a number of genes
do contribute speciﬁcally to pollen grain formation.
For instance, pollen development can be interrupted at
differentdevelopmentalstages in certain plant mutants
which have no vegetative phenotype [5, 13]. Fur-
thermore, silencing of speciﬁc anther and/or pollen-
The nucleotide sequence of data reported will appear in the
EMBL Nucleotide Sequence Database under the accession number
X95984 (SB401 cDNA).
expressed genes by antisense or co-suppression also
gaverise to aberrant pollen grains and resulted in gam-
etophytic sterility [25, 35].
Genes speciﬁcally expressed during pollen devel-
opment have been classiﬁed into two main groups:
the ‘early’ genes (expressed between meiosis and the
ﬁrst microspore mitosis) and the ‘late’ genes (ﬁrst
expressed after microspore mitosis) . As there is
also some overlapbetween the expressionof these two
groups of genes, the classiﬁcation according to tem-
poral gene expression pattern is not absolute. The tran-
scripts of the ‘late’ genes accumulate to a high level at
in pollen germination and initial pollen tube growth.
A pool of pre-synthesized messenger RNAs is stored
in mature pollen grains and some of these messengers
may not be translated before pollen germination [3,
22, 33]. These pre-synthesized messenger RNAs are