Plant Molecular Biology 37: 187–192, 1998.
1998 Kluwer Academic Publishers. Printed in Belgium.
A maize pectin methylesterase-like gene, ZmC5, speciﬁcally expressed in
, H.J. Rogers
, M. Rozycka
School of Biological Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey TW20 OEX,
author for correspondence);
Zeneca Seeds, Jealott’s Hill Research Station, Bracknell, Berks RG12 6EY,
Present address: School of Pure and Applied Biology, University of Wales, Cardiff, P.O. Box 915, Cardiff
CF1 3TL, UK
Received 27 May 1997; accepted in revised form 8 December 1997
Key words: pollen, pectin methylesterase, microsporogenesis
Pectin methylesterase (PME) is responsible for the demethylation of pectin prior to pectin’s degradation by the
combined activities of polygalacturonase and pectate lyase. We have differentially screened a maize pollen cDNA
library to detect cDNA clones whose genes are speciﬁcally expressed in pollen. One group of clones resulting
from this screen showed similarity (between 18% and 41% identity) with plant and fungal PMEs. The full-length
clone from this group, ZmC5, identiﬁes a small gene family (at least 2 members) when used as a probe on
genomic Southern blots. Northern analysis reveals that the ZmC5 transcript is expressed speciﬁcally in late pollen
development. This tissue-speciﬁc gene expression programme is further conﬁrmed in transgenic tobacco plants
harbouring ZmC5 promoter/GUS chimeric gene constructs.
Many of the characterisedgenes whichare speciﬁcally
or highly expressed in pollen and germinating pol-
len encode proteins that are likely to play a role in
cell wall metabolism, for example the genes that are
homologous to enzymes involved in pectin degrada-
tion, polygalacturonases [3, 24], pectate lyase [20, 26]
and pectin methylesterase (PME EC 184.108.40.206), .
Other genes highly expressed in pollen include those
that encode cytoskeletal proteins [12, 21, 23], putat-
ive ascorbate oxidases, a Kunitz protein inhibitor and
many others whose function cannot be inferred by
homology to known genes . The temporal expres-
sion of such genes has been studied and they are found
to be expressed late in microsporogenesis reaching a
maximum in mature microsporocytes. In some cases
continued expression in the pollen tube has also been
demonstrated . These genes have been termed ‘late
genes’. Most of the expression at this stage is from the
Thenucleotidesequencedatareportedwill appear in the EMBL,
GenBankandDDBJ Nuceotide Sequence Databases under the acces-
sion number Y13285.
vegetative cell rather than from the generative cell and
it is likely that the majority of these ‘late’ genes are
transcribed from the vegetative nucleus, although this
has only been demonstrated for one late gene . A
distinct class of genes expressed in anthers is found
to have a different expression programme, being ﬁrst
detectable soon after the tetrad stage and declining
in expression well before pollen maturity. It is likely
that the major role of these ‘early’ genes may be dur-
ing microspore differentiation and development rather
than pollen tube growth.
Here we describe a ‘late’ pollen expressed gene
from maize, ZmC5, which, like two other pollen
napus , shows signiﬁcant identity with known PME
genes from the plant pathogens Erwinia chrysanthemi
 and Pseudomonas solanacearum .