Plant Molecular Biology 42: 559–569, 2000.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.
Molecular characterization of a hydroxymethylglutaryl-CoA reductase
gene from mulberry (Morus alba L.)
Ashok K. Jain
, Rebecca M. Vincent and Craig L. Nessler
Department of Biology, Texas A&M University, 315 Biological Science Building W, College Station, TX 77843-
3258, USA (
author for correspondence);
Present address: Plant Biotechnology Laboratory, Division of
Agricultural Sciences, Florida A&M University, Tallahassee, FL 32304, USA
Received 1 May 1999; accepted in revised form 17 November 1999
Key words: abscisic acid, HMGR, isoprenoid,light regulation, Morus alba, mulberry, hydroxymethylglutaryl-CoA
The genus Morus consists of trees and shrubs, which are distributed in temperate and subtropical regions. Com-
monly known as mulberry, a few of the Morus species are valued for their foliage, which constitutes the chief feed
for mulberry silkworms. Steroids and isoprenoid compounds present in the foliage not only add nutritive factors
to the feed but also contribute greatly to silkworm health and silk production. Mevalonate synthesis, which is the
ﬁrststep in isoprenoidbiosynthesis, is catalyzedby the enzymehydroxymethylglutaryl-CoAreductase(HMGR).A
genomicclone, Mahmg1,wasisolated from Morus alba and its expression characterized in mulberryand transgenic
tobacco. In mulberry, Mahmg1 transcripts were highest in young leaves and ﬂowers. The promoter region of the
Mahmg1 gene was fused to the β-glucuronidase (GUS) reporter gene and the fusion introduced into tobacco.
In imbibed embryos, GUS expression was limited to the cotyledons, epicotyl, and root elongation zone. Later,
GUS staining was observed in ﬂoral tissues, guard cells, and the heads of trichomes on the stem and petioles.
Mahmg1::GUS activity increased 3–4-fold by treatment with 100 µM abscisic acid and 15–80-fold in dark-grown
versus light-grown seedlings. These results show that expression of the Mahmg1 gene is differentiallyregulated by
developmentaland environmentalcues, suggesting that its HMGR isozyme a may providea precursor for synthesis
of speciﬁc isoprenoids during mulberry growth and development.
Over 22000 isoprenoids have been identiﬁed in plants
and many of these compounds are vital to nor-
mal plant growth and development (Chappell, 1995).
Hydroxymethylglutaryl-CoA reductase (HMGR, EC
220.127.116.11) is a key regulatory enzyme, which provides
the backbone from which isoprenoids are synthesized
(Chappell et al., 1995).
HMGR has been examined in a wide variety of
plant species at the biochemical and molecular lev-
els. Genes encoding HMGRs have been isolated and
characterized from many plant species including Ara-
The nucleotide sequence data reported will appear in the EMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accenssion number U43711.
bidopsis (Enjuto et al., 1994, 1995), tomato (Park
et al., 1992), potato (Korth et al., 1997), and wheat
(Aoyagi et al., 1993). Unlike animals, which have
single-copy hmgr genes (Gertler et al., 1988), plant
hmgr usually occurs in small gene families and al-
though the proteins they encode may share high se-
quence identity, the expression patterns of individual
family members are generally distinct (reviewed in
Stermer et al., 1994).
Mulberry (Morus sp.) is a perennial woody plant
of considerable economic importance because of its
foliage, which constitutes the chief food for the mul-
berry silkworm (Bombyx mori L.). We are interested
in mulberry HMGR because of its pivotal role in the
synthesis of a wide variety of metabolites beneﬁcial to