Agriculture Reference
In-Depth Information
into the possibility of transgenic approaches to
improve various traits. Drought tolerance has
been studied transgenically by insertion of the
yeast
trehalose-
6-
phosphate synthase
1
gene (Kon-
drák
et al
., 2011), the Arabidopsis
dehydroascor-
bate reductase gene
(Eltayeb
et al
., 2011), a
betaine
aldehyde dehydrogenase
(
BADH
) gene from
spinach (Zhang
et al
., 2011), or constitutive ex-
pression of the potato
StMYB1R-
1
transcription
factor (Shin
et al
., 2011). In addition, Waterer
et al
. (2010) investigated the effect of wheat
mitochondrial
Mn superoxide dismutase
(SOD3:1),
barley
dehydrin
4
(DHN 4), a canola transcrip-
tional factor (
DREB/CBF1
), or a bromegrass
stress-inducible
ROB5
gene in potato cultivar
Desiree. The transgenes were placed under the
control of either the constitutive P35S promoter
or a stress-inducible Arabidopsis COR78 pro-
moter. The promoter/transgene combinations,
COR78:DHN4 and COR78:ROB5, were the most
likely to enhance tuber yield under drought
stress. Kim
et al
. (2011) inserted into potato cul-
tivar Atlantic a peroxiredoxin gene (
2-
Cys Prx
)
from Arabidopsis controlled by either the consti-
tutive P35S promoter or the stress-inducible
PSWPA2 promoter from sweet potato. The trans-
genics were more tolerant to heat shock than
untransformed controls, and the stress-inducible
promoter resulted in greater expression of the
transgene than P35S. Stacking antioxidant genes
may provide greater protection against multiple
stress conditions than deploying single genes
(Ahmad
et al
., 2010). The strategy of using stress-
inducible promoters restricts expression of the
transgene to conditions when resistance is needed,
with the intention of economizing physiological
processes and avoiding the undesirable effects
of transgene expression during non-stress
conditions.
Improvement of salt stress tolerance of potato
has also been the target of considerable transgenic
research in recent years. Bayat
et al
. (2010) re-
ported improved
in vitro
salt tolerance for potato
cultivars transformed with a barley antiporter
gene,
HvNHX2
. Overexpression of the
GalUR
gene,
an ascorbic acid pathway enzyme, provided potato
cultivar Taedong Valley with enhanced tolerance
to salt stress, as measured by growth and microtu-
berization of
in vitro
plantlets (Upadhyaya
et al
.,
2011). The Arabidopsis transcription factor,
At-
DREB1A
, under the control of a stress-inducible
Arabidopsis promoter (
rd294
) in potato cultivar
Desiree, conferred salinity tolerance relative to
the level of expression of
AtDREB1A
under salt
stress conditions (Celebi-Toprak
et al
., 2005;
Watanabe
et al
., 2011). These initial studies of
transgenics using stress response genes, identi-
fied through the application of transcriptomic
and proteomic tools in model plants as well as in
potato, suggest a new wave of commercial trans-
genic potatoes with wide environmental adapta-
tion in the near future.
Resistance against biotic stress has been
emphasized in transgenic studies in recent years
as well. Defense against fungal pathogens has
been illustrated by the insertion of thionin genes
from brassicaceous species into potato, which
was reported to express increased resistance to
gray mold (
Botrytis cinerea
) (Hoshikawa
et al
.,
2012). The
StoVe1
gene from an aubergine spe-
cies was overexpressed to reduce the infection
rate of
Verticillium dahliae
on potato cultivar De-
siree (Liu
et al
., 2012). Likewise, expression of
both chitinase (chiA) and ribosome inactivating
protein (rip30) was combined to enhance the re-
sistance of potato to
Rhizoctonia solani
(M'Hamdi
et al
., 2012). In another study, the
Rpi-bt1
resist-
ance gene from
S. bulbocastanum
under the con-
trol of a potato ubiquitin promoter conferred
resistance to late blight (Oosumi
et al
., 2009).
A new source of transgenic resistance to PVY
was found in the construction of a recombinant
heavy chain variable region (VH antibody) with
added hydrophobic residues targeting cytosolic
expression (Bouaziz
et al
., 2009). Stacking of re-
sistance genes by inserting a double gene con-
struct (
Nicotiana tabacum
AP24 osmotine and
Phyllomedusa sauvagii
dermaseptin) into potato,
followed by retransformation with a
Gallus gallus
lysozyme construct, yielded plants that were
highly resistant to
Erwinia carotovora
and in-
hibited fungal growth (Rivero
et al
., 2012).
Pest resistance as well as pathogen resist-
ance has been the focus of several studies on
transgenic potato. The different crystal (cry) en-
dotoxins produced by the soil bacterium,
Bacillus
thuringiensis
, have been used to convey trans-
genic resistance to several insect pests of potato
(Pardo-López
et al
., 2013). Various
cry
genes,
including
cry1Ab
under the control of a tuber-
specific, granule-bound starch synthase (GBSSi)
promoter (Kumar
et al
., 2010), or a light-inducible
phosphoenolpyruvate carboxylae (PEPC) pro-
moter (Hagh
et al
., 2009), and
cryIIa1
with a
