Plant Molecular Biology 35: 855–864, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
Structure and speciﬁc expression of a Nicotiana sylvestris putative
amino-acid transporter gene in mature and in vitro germinating pollen.
, Chantal Mathieu, Odile Roche, Fernand Vedel and Rosine De Pape
Institut de Biotechnologie des Plantes, ERS 569, Universit
at. 630, 91405 Orsay Cedex, France;
Present address: Botany Department, Leicester University, University Road, LE1 7RH Leicester, UK (
Received 11 March 1977; accepted in revised form 25 July 1997
Key words: amino acid transporter, gene sequence, in vitro pollen germination, in situ hybridization, Nicotiana
sylvestris, pollen-speciﬁc expression
We report here the structure and expression analysis of a Nicotiana sylvestris gene, called nsaap1, coding for a
protein which shows signiﬁcant identity to the members of the Arabidopsis thaliana amino acid permease family.
The nsaap1 gene is expressed exclusively in binucleate pollen. Its transcripts begin to accumulate after ﬁrst pollen
mitosis and dramatically increase in mature pollen shortly before anthesis and during in vitro pollen germination.
The nsaap1 5
-ﬂanking region contains long regions homologous to the promoter region of the tobacco pollen
speciﬁc eIF-4A8 translation factor. Our results support the occurrence of an amino acid remobilization in binucleate
pollen. The nsaap1 gene could play a role in exchanges between the vegetative and the generative pollen cells.
Male gametogenesisin plants is an energy-consuming
developmental process, at the end of which the mature
pollen must be able to germinate and perform fertil-
ization. After meiosis, the haploid microspore under-
goes an asymmetric mitotic division which results in
the formation of two highly differentiated cells (Fig-
ure 1): a large vegetative cell, which provides energy
and metabolites, and a small generative cell, essen-
tially metabolically inactive, that is enclosed with-
in the vegetative cell [reviewed in 3]. In most plant
species, the division of the generative cell leading to
the formation of the two sperm cells occurs after pol-
len tube germination. This short but highly complex
pattern involves the intervention of numerous speciﬁc
genes. It has been calculated from reassociation kinetic
studies that about 2500 different genes are speciﬁcally
expressed in the developing male gametophyte .
A ﬁrst group of genes is expressed throughout gam-
The nucleotidesequence data reported will appear in the EMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accession number U64823.
etophytic development. A second group of transcripts
(early genes) accumulates soon after the meiosis and
decreases prior to pollen maturity . The third group
of transcripts (late genes) starts accumulating after the
microsporemitosis [1, 16, 34, 37] and increases during
pollen maturation. These are thought to be translated
during pollen germination and pollen tube growth. It
has been deduced from previous inhibition studies that
pollen tube growth depends essentially on translation
rather than transcription of a new set of genes [9, 23,
A fundamental question concerning pollen devel-
opment is how the vegetative cell stores and remo-
bilizes its basic metabolites in preparation for rapid
pollen tube growth. Physiological evidence suggests
that exchanges of metabolites, such as amino acids
and sugars, occur in pollen cells but remain to be
demonstrated. Speciﬁc amino acid transport activit-
ies have been identiﬁed in different cell types, such
as in the plasmalemma of zucchini hypocotyls  and
in tonoplast membranes from sugar beet leaves ,
but were never described in pollen. Recently, cDNAs
encoding three different kinds of plasma membrane-