Biomedical Engineering Reference
In-Depth Information
lesser effect. The expression level of endochitinase but exochitinase was
correlated with disease resistance. Nevertheless, exochitinase enhanced
the effect of endochitinase on disease resistance when the two genes
co-expressed in transgenic plants. Resistance to
Magnaporthe grisea
was
found in all kinds of regenerated plants including that with single
gluc78
.
A few lines expressing either
ech42
or
nag70
genes were immune to the
disease (Liu et al. 2004). Two transgenic lemon clones with the
chit42
gene
from
Trichoderma
harzianum
were tested for resistance to fungal disease
and expression level of defence-related genes was evaluated (Distefano
et al. 2008). Leaves of transgenic lemon plants inoculated with
B.
cinerea
showed signifi cantly less lesion development than wild type leaves.
Tissues from detached leaves of different transgenic lemon clones showed
a signifi cant correlation between resistance and transgene expression. On
the other hand, the over-expression of the transgenic fungal gene enhanced
by two-three folds transcript levels of genes associated with enhanced
ROS production and ISR establishment, while the expression of native
chitinase and glucanase genes involved in SAR was down-regulated.
Vishnevetsky et al. (2011) developed a transformation system for banana
and expressed the endochitinase gene
ThEn-42
from
Trichoderma
harzianum
together with the grape stilbene synthase (StSy) gene in transgenic
banana plants under the control of the 35S promoter and the inducible
PR-10 promoter, respectively. The superoxide dismutase gene Cu,Zn-SOD
from tomato, under control of the ubiquitin promoter, was added to this
cassette to improve scavenging of free radicals generated during fungal
attack. A 4-year fi eld trial demonstrated several transgenic banana lines
with improved tolerance to Sigatoka disease. The best transgenic lines
exhibiting Sigatoka tolerance were also found to have tolerance to
B.
cinerea
in laboratory assays.
In addition to biotic stress tolerance, several genes from
Trichoderma
spp.
have also been successfully deployed in transgenic plants for improving
tolerance to abiotic stresses. Montero-Barrientos et al. (2010) expressed
the
T. harzianum
heat shock protein gene (
hsp70
) in Arabidopsis. The
transgenic seedlings were more tolerant to osmotic, salt and oxidative
stresses with respect to the wild-type behavior. Transgenic lines also had
increased transcript levels of the Na(+)/H(+) exchanger 1 (SOS1) and
ascorbate peroxidase 1 (APX1) genes, involved in salt and oxidative stress
responses, respectively. Similarly, Hermosa et al. (2011) reported that
expression of the
Thkel1
, which codes for a putative kelch-repeat protein
gene in Arabidopsis enhances plant tolerance to salt and osmotic stresses,
accompanied by an increase in glucosidase activity and a reduction of
abscisic acid levels compared to those observed in wild-type plants.
Recently, a
T. virens
gene for glutathione transferase (TvGST) has been cloned
and transferred to transgenic tobacco (Dixit et al. 2011a). When transgenic
