Plant Molecular Biology 33: 729–735, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
Expression patterns of vascular-speciﬁc promoters RolC and Sh in
transgenic potatoes and their use in engineering PLRV-resistant plants
Michael W. Graham, Stuart Craig and Peter M. Waterhouse
CSIRO Division of Plant Industry, GPO Box 1600, Canberra, 2601, Australia (
author for correspondence)
Received 9 August 1995; accepted in revised form 22 October 1996
Key words: phloem-speciﬁc gene expression, potato leafroll virus (PLRV) resistance, RolC promoter, Shrunken
promoter, sucrose synthase-1 promoter, vascular-speciﬁc gene expression
The expression patterns of GUS fusion constructs driven by the Agrobacterium rhizogenes RolC and the maize
Sh (Shrunken; sucrose synthase-1) promoters were examined in transgenic potatoes (cv. Atlantic). RolC drove
high-level gene expression in phloem tissue, bundle sheath cells and vascular parenchyma, but not in xylem or
non-vascular tissues. Sh expression was exclusively conﬁned to phloem tissue. Potato leafroll luteovirus (PLRV)
replicates only in phloem tissues, and we show that when RolC is used to drive expression of the PLRV coat protein
gene, virus-resistant lines can be obtained. In contrast, no signiﬁcant resistance was observed when theSh promoter
The CaMV 35S promoter has been widely used in
plant genetic engineering since it driveshigh level con-
stitutive expression of transgenes. Such an expression
pattern is generally thought to be advantageous for
engineering viral resistance and 35S derivatives have
consequentlybecome the promoters of choice for driv-
ing expression of viral resistance constructs.
There are, however, compelling reasons for using
promoters other than 35S for engineering viral resist-
ance. For example, a number of plant viruses, such as
the luteoviruses, reoviruses and most geminiviruses,
replicate exclusively in phloem-associated tissue. For
such viruses phloem-speciﬁc expression of virus res-
istance genes is desirable since constitutive expression
might unnecessarily increase the risks of transcapsid-
ation or viral recombination  in non-vascular tis-
sues. Furthermore, phloem-speciﬁc gene expression
may impose a decreased metabolic load on the plant.
In addition, complexapplicationsin biotechnology,
such as engineering multiple characters or pyramiding
resistance genes, will increasingly require the use of
banks of promoters with deﬁned temporal, spatial and
developmental speciﬁcities. One important considera-
tion is transgene silencing , which can result from
somatic interactions between repeated transgene pro-
moter sequences ; it seems unwise to engineer
plants expressing multiple transgenes all driven by the
same promoter. Patent issues are also a concern for the
commercial use of 35S.
We areinterestedinengineering resistancetopotato
leafroll virus (PLRV) and other luteoviruses .
These viruses are thought to replicate exclusively in
phloemcells; viral particles are only found in seive ele-
ments and companion cells, but it is unclear which cell
types support viral replication. In this paper we com-
pare the patterns of expression of two vascular-speciﬁc
promoters in transgenic potatoes. We also examine the
utility of these promoters in driving PLRV resistance
using a PLRV coat protein construct.
We chose two promoters for this study, the
Agrobacterium rhizogenes RolC promoter and the
maize Sh (Shrunken; sucrose synthase-1) promoter.
The RolC promoter has been reported to drive phloem-
speciﬁc gene expression in both tobacco  and rice
. The Sh promoter is a monocot promoter which
was shown to drive phloem cell-speciﬁc GUS expres-
sion in transgenic tobacco .