Rice War Continues
Editor’s note
The productivity of rice has been falling along with that of other food
grains. Chief among the causes of the fall in productivity are severe water
shortages due to over-irrigation and depletion of aquifers, eroded soils from
over-application of chemical fertilizers and pesticides, and rising
temperatures from global warming.
While innovative farmers have been addressing these problems with a
range of effective measures to increase yields through regenerating degraded
soils, conserving water and minimizing inputs (see many articles in
SiS23), pro-GM
scientists in the three major rice-growing countries, China, India and Japan,
have all been researching and promoting GM rice with scant regard for safety or
sustainability.
We are circulating Professor Joe Cummins’ review on GM rice in
China, and making available two others, on GM rice in India and Japan
respectively on ISIS’ website:
GM Rice in Japan
GM Rice in India
ISIS Press Release 30/11/04
GM Rice in India
Prof. Joe Cummins reviews recent genetically modified rice research
in India.
References for this
article are posted on ISIS members’ website.
Details here.
India is the second largest consumer of rice on the globe after China,
and more than twice that of the next country, Indonesia [1]. India produced 93
million tonnes of rice in 2001 and 2002, and the government is targeting 129
million tonnes by 2011 and 2012 [2]. India approved genetically modified (GM)
cotton for food, feed and fiber in 2002 and other approvals may soon follow
[3]. A lot of technically sophisticated research on GM rice is being done in
India, and I shall describe some of it here. Currently, no GM rice variety has
been commercially released in India.
An extensive review exists on the production of transgenic rice up to
the year 2000 [4]; I shall therefore concentrate on some important studies
published since.
Insect resistant rice
Elite Indica transgenic rice containing a synthetic gene from
Bacillus thuringiensis (Bt) expressing Cry1Ac toxin had enhanced
resistance to stem borer. The cry gene was driven by the ubiquitin
promoter from maize and its transcription was terminated by the terminator of
the nos gene from Agrobacterium, tnos; and accompanied by
an antibiotic (hygromycin) resistance gene and the bacterial gus gene as
negative and positive selection markers respectively. The transformed rice
lines had up to 0.25% of their total protein as Cry1Ac toxin. The successful
lines caused 100% mortality when consumed by yellow stem borer larvae [5].
Production of toxin at high levels (approaching 1% of the cellular protein) is
considered important in preventing resistance in the target insect, but that
will mean a lot of toxin consumed by humans eating the rice. Cry1Ac is known to
be a strong immunogen [6], and has also been found to be sufficiently similar
to known allergens to cause concern [7].
Stacked and pyramided insect, fungi and bacterial resistant rice
Following development of rice with single transgenic traits, it is
inevitable that transgenic varieties with multiple traits would appear,
produced by gene stacking or multiple transformations of a transgenic line, or
by crossing transgenic lines to combine their transgenes. It appears from
current research that varieties with multiple transgenes will soon exceed
varieties with single transgenic traits.
A stacked combination of Bt toxins Cry1Ab and Cry1Ac along with
tolerance to the herbicide glufosinate (bar gene) was created in order
to serve as a parental line for generating hybrid rice varieties. The
bar gene was driven by the CaMV promoter and terminated by tnos.
Both cry genes were synthetic and driven by the maize ubiquitin promoter
and terminated with tnos. The two cry gene cassettes, each
accompanied by the bar cassette, were transformed from different
plasmids and ended up at different sites in the rice genome. The resultant
transgenic line was resistant to stem borer insects and to the herbicide
glufosinate [6]. An Indica rice variety was stacked with cry1Ab
and cry1Ac, plus the snowdrop lectin gene gna conferring multiple
resistance to insects and all of these were joined to the bar gene for
glufosinate tolerance with the CaMV promoter and tnos terminator. The
cry genes were driven by the maize ubiquitin promoter and terminated
with tnos while the gna gene was driven by phloem-specific
rice-sucrose synthase promoter and terminated by tnos. The cry
genes and the gna gene were inserted at different sites in the rice
genome [7]. The stacked rice variety was assumed to confer strong
insect-killing power and to guard against appearance of insect resistance.
An elite Indica rice was modified for resistance to insects,
fungal disease and bacterial disease. One parental strain contained the xa21
gene conferring resistance to bacterial blight. The gene was isolated from
wild rice and used to transform rice, accompanied by its original promoter and
terminator. Another parental strain had a rice chitinase gene for protection
against the sheath blight fungus and a synthetic cry gene consisting of
the fused active portions of cry1Ab and cry1Ac to protect against
yellow stem borer. The fused cry gene and the chitinase gene were
integrated at the same site on the rice genome. The cry fusion gene was driven
by the maize ubiquitin promoter and the chitinase gene was driven by the CaMV
promoter. The two parental lines were combined by crossing to create the
pyramided strain resistant to three kinds of pathogens, insect, fungus and
bacteria [8].
Another technique, marker assisted selection, has been combined with
pyramiding and stacking to produce rice resistant to fungal blast and bacterial
blight. Marker assisted selection is traditional breeding assisted by molecular
markers in the rice genome which are used to follow desirable genes in a cross.
Two rice genes for blast resistance were identified and pyramided, and both of
the pyramided lines were stacked by modification with the rice xa21 gene
accompanied by a bacterial hygromycin resistance gene driven by a CaMV
promoter. The rice pyramid was resistant to both blast and blight [9].
Pyramiding, stacking and fusing genes are being used with a vengeance against
pests, with little consideration for the safety of the rice, which would be
consumed as food.
Novel genetic approaches
The plant’s natural defense against pests includes an oxidative
burst mediated by hydrogen peroxide. Such a burst may mean suicide for the
plant cell and a few neighboring cells; but it saves the plant from the
invading pest. A fungal glucose oxidase (gox) gene was used to release
hydrogen peroxide in the transformed rice, driven by a rice wound inducible
promoter. The transformation also included a bacterial hygromycin resistance
gene as a selectable marker. A transformant was resistant to both bacterial and
fungal pests; and the resulting rice strain had broad-spectrum disease
resistance [10].
Flavonoid pigments such as a purple anthocyanin pigment from maize have
been found to increase blast resistance. A maize gene for an enzyme triggering
purple pigment production was used to transform rice, under the control of a
rice actin promoter and accompanied by a bacterial hygromycin resistance gene
driven by a CaMV promoter [11]. The purple rice resisted rice blast.
Drought limits crop yields. A barley gene hva1 protects the cell
membrane during drought, and when inserted in rice, could reduce drought
damage. The rice was transformed with the barley hva1 gene, driven by
the rice actin promoter and terminated with a potato protease terminator. The
rice transformation also included the bar gene for herbicide tolerance
as a selectable marker driven by a CaMV promoter and terminated with
tnos. The transgenic crop showed greater growth than the non-transgenic
line under drought conditions [12].
Heat tolerance is important in most rice producing countries. It has
been found that a heat shock protein (hsp 100) is produced during heat stress.
By over expressing the rice hsp100 gene, it was possible to increase
growth under high temperatures. Basmati rice was transformed with the
Arabidopsis hsp101 gene driven by a maize ubiquitin promoter and first
intron and transcription terminated by tnos; it was accompanied by a
hygromycin resistance marker driven by a CaMV promoter and terminated by
tnos. The transgenic rice performed better than the parent strain in
heat and in recovery from heat shock [13].
GM research outpacing safety tests
While the GM rice being researched in India may show some promise in
providing pest and disease resistance, or tolerance to abiotic stress, it is
clear that research has raced ahead of safety considerations. As rice is
consumed as a staple food, any GM rice considered for commercialization must
undergo a thorough pre-market safety assessment and have its safety proven
beyond reasonable doubt.
Some areas of especial concern include the use of Bt biopesticides that
are potentially toxic and allergenic (see "GM rice release in China?", this
series); and the complicated, multiple traits that may be especially prone to
genetic instability through illegitimate recombination. Furthermore, not only
the effects of each of the genes, but also their combined effects must be
adequately tested for safety.
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