Plant Molecular Biology 48: 223–231, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Wound-response regulation of the sweet potato sporamin gene promoter
Shu-Jen Wang, Yi-Ching Lan, Shih-Fung Chen, Yih-Ming Chen and Kai-Wun Yeh
Department of Botany, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipe 107, Taiwan (∗author
for correspondence; e-mail email@example.com)
Received 21 April 2000; accepted in revised form 28 July 2001
Key words: octadecanoid signal transduction pathway, sporamin, sweet potato, transgenic tobacco, wound
Sporamin, a tuberous storage protein of sweet potato, was systemically expressed in leaves and stems by wound
stimulation. In an effort to demonstrate the regulatory mechanism of wound response on the sporamin gene, a
1.25 kb sporamin promoter was isolated for studying the wound-induced signal transduction. Two wound response-
like elements, a G box-like element and a GCC core-like sequence were found in this promoter. A construct
containing the sporamin promoter fused to a β-glucuronidase (GUS) gene was transferred into tobacco plants by
Agrobacterium-mediated transformation. The wound-induced high level of GUS activity was observed in stems
and leaves of transgenic tobacco, but not in roots. This expression pattern was similar to that of the sporamin gene
in sweet potatoes. Exogenous application of methyl jasmonate (MeJA) activated the sporamin promoter in leaves
and stems of sweet potato and transgenic tobacco plants. A competitive inhibitor of ethylene (2,5-norbornadiene;
NBD) down-regulated the effect of MeJA on sporamin gene expression. In contrast, salicylic acid (SA), an inhibitor
of the octadecanoid pathway, strongly suppressed the sporamin promoter function that was stimulated by wound
and MeJA treatments. In conclusion, wound-response expression of the sporamin gene in aerial parts of plants is
regulated by the octadecanoid signal pathway.
Abbreviations: GUS, β-glucuronidase; MeJA, methyl jasmonate; NBD, 2,5-norbornadiene; SA, salicylic acid;
ABA, abscisic acid
Sporamin is the most abundant protein in the tuberous
roots of sweet potato and is thought to be a stor-
age protein that functions as a nutritional resource for
tuberous root germination (Maeshima et al., 1985;
Hattori et al., 1989). On the other hand, sporamin
was found to strongly inhibit trypsin activity (Yeh
et al., 1997a), and insect-defense capabilities were
conﬁrmed in insect bioassays with transgenic tobacco
(Yeh et al., 1997b) and cauliﬂower (Ding et al., 1998).
These results suggested that sporamin functions not
only as a storage protein for nutrient supply but also
as a factor against herbivore attacks. Thus far, at
least ten sweet potato sporamin genes have been iso-
lated and characterized (Hattori et al., 1989; Chen
et al., 1997). These genes belong to a large multi-
gene family that is divided into subfamilies A and B.
There is over 90% nucleotide homology among intra-
subfamily genes, and about 80% nucleotide homology
among inter-subfamily genes (Hattori et al., 1989).
In ﬁeld-grown plants, sporamin was shown to be
strongly associated with tuberous roots, with only very
low amounts produced in stems, and almost none in
leaves (Maeshima et al., 1985; Chen et al., 1997).
However, large amounts of sporamin were accumu-
lated in leaf-petiole cuttings under high concentrations
of sucrose, glucose or fructose cultured conditions