Reducing progoitrin and enriching glucoraphanin in Brassica
napus seeds through silencing of the GSL-ALK gene family
Arvind H. Hirani
Peter B. E. McVetty
Carlos F. Quiros
Received: 7 July 2010 / Accepted: 14 March 2012 / Published online: 3 April 2012
Ó Springer Science+Business Media B.V. 2012
Abstract The hydrolytic products of glucosinolates in
brassica crops are bioactive compounds. Some glucosinolate
derivatives such as oxazolidine-2-thione from progoitrin in
brassica oilseed meal are toxic and detrimental to animals, but
some isothiocyanates such as sulforaphane are potent anti-
carcinogens that have preventive effects on several human
cancers. In most B. rapa, B. napus and B. juncea vegetables
and oilseeds, there is no or only trace amount of glucoraph-
anin that is the precursor to sulforaphane. In this paper, RNA
interference (RNAi) of the GSL-ALK gene family was used to
down-regulate the expression of GSL-ALK genes in B. napus.
The detrimental glucosinolate progoitrin was reduced by
65 %, and the beneﬁcial glucosinolate glucoraphanin was
increased to a relatively high concentration (42.6 lmol g
seed) in seeds of B. napus transgenic plants through silencing
of the GSL-ALK gene family. Therefore, there is potential
application of the new germplasm with reduced detrimental
glucosinolates and increased beneﬁcial glucosinolates for
producing improved brassica vegetables.
Keywords Brassica napus Á Glucosinolates Á
Gene silencing Á GSL-ALK genes
Glucosinolates are secondary plant products that are syn-
thesized in the order Capparales. The hydrolytic breakdown
products of glucosinolates, especially isothiocyanates, are
beneﬁcial bioactive constituents that have cancer-pre-
ventive properties in humans, that contribute to ﬂavors in
brassica vegetables and condiments and that are used as
biopesticides in biofumigation. In contrast, in rapeseed
meal, the dominant glucosinolate progoitrin (2-hydroy-
3-butenyl glucosinolate) is changed into an oxazolidine-2-
thione, which causes goiter and has other detrimental
effects on animal health. Therefore, enrichment of beneﬁ-
cial glucosinolate and reduction of detrimental glucosino-
lates are given great attention in Brassica crops’ breeding.
In canola, progoitrin has been dramatically reduced
through conventional breeding although it might be reduced
further through gene manipulation (Liu et al. 2010). In
broccoli and a few other B. oleracea vegetables, gluco-
raphanin predominates and its hydrolysis product, sulfora-
phane, is identiﬁed as a potent anticarcinogenic compound.
For this reason, sulforaphane has been extensively investi-
gated due to its potent cancer-preventive effects (Fahey et al.
1997; Shapiro et al. 2001; Zhang et al. 1992). Sulforaphane
also induces apoptosis in cancer cells through inhibition of
histone deacetylase, which leads to cancer cell cycle arrest
(Gamet-Payrastre et al. 2000). Increasing interest in gluco-
sinolates and their degradation products is due to their
potential as human cancer-prevention agents, crop-protec-
tion compounds and biofumigants in agriculture.
High concentrations of glucoraphanin are only found in
broccoli and several other B. oleracea vegetables such as
kale, Chinese kale, cabbage and purple cauliﬂower (Li
et al. 2001). In B. oleracea, glucoraphanin concentration
was enriched through conventional breeding (Mithen et al.
Zheng Liu and Arvind H. Hirani: contributed equally to this work.
Electronic supplementary material The online version of this
article (doi:10.1007/s11103-012-9905-2) contains supplementary
material, which is available to authorized users.
Z. Liu Á A. H. Hirani Á P. B. E. McVetty Á F. Daayf Á G. Li (&)
Department of Plant Science, University of Manitoba,
Winnipeg R3T2N2, Canada
C. F. Quiros
Department of Plant Sciences, University of California,
Davis, CA 95616, USA
Plant Mol Biol (2012) 79:179–189