Biomedical Engineering Reference
In-Depth Information
the scab pathogen
Venturia inequalis
. Disease severity compared with cv.
Marshall McIntosh was reduced by 0 to 99.7% (number of lesions), 0 to
90% (percentage of leaf area infected) and 1 to 56% (conidia recovered) in
the transgenic lines tested. Endochitinase also had negative effects on the
growth of both inoculated and uninoculated plants. There was a signifi cant
negative correlation between the level of endochitinase production and
both the amount of disease and plant growth (Bolar et al. 2000). Genes
from the biocontrol fungus
Trichoderma
atroviride
encoding the antifungal
proteins endochitinase or exochitinase (N-acetyl-beta-D-hexosaminidase)
were inserted into 'Marshall McIntosh' apple singly and in combination.
(Bolar et al. 2001). The level of expression of endochitinase was negatively
correlated with plant growth while exochitinase had no consistent effect
on this character. Plants expressing both enzymes simultaneously were
more resistant than plants expressing either single enzyme at the same
level, analyses indicated that the two enzymes acted synergistically to
reduce disease. The orthologous gene (
ech42
) from another species of
Trichoderma
(
T. virens
) was introduced to cotton plants and homozygous
T2 plants of the high endochitinase-expressing cotton lines were tested
for disease resistance against a soil-borne pathogen,
Rhizoctonia solani
and
a foliar pathogen,
Alternaria alternata
. Transgenic cotton plants showed
signifi cant resistance to both pathogens (Emani et al. 2003). Subsequently,
biochemical and molecular analyses conducted on the transgenic plants
showed rapid/greater induction of ROS, expression of several defense-
related genes and activation of some PR enzymes and the terpenoid
pathway (Kumar et al. 2009). Interestingly, even in the absence of a
challenge from the pathogen, the basal activities of some of the defense-
related genes and enzymes were higher in the endochitinase-expressing
cotton plants. This elevated defensive state of the transformants may act
synergistically with the potent, transgene-encoded endochitinase activity
to confer a strong resistance to
R. solani
infection. The same gene was also
introduced in rice and high level of resistance against
R. solani
could be
obtained (Shah et al. 2009). The
ech42
gene from an Indian isolate of
T. virens
was cloned and expressed in transgenic tobacco and tomato and exhibited
resistance against the fungal pathogens
Alternaria alternata
,
Botrytis cinerea
and
Sclerotinia sclerotiorum
(Shah et al. 2010). Three genes encoding for
fungal cell wall degrading enzymes (CWDEs),
ech42
,
nag70
and
gluc78
from the biocontrol fungus
Trichoderma
atroviride
were inserted into the
binary vector pCAMBIA1305.2 singly and in all possible combinations
and transformed to rice plants. More than 1800 independently regenerated
plantlets in seven different populations (for each of the three genes and
each of the four gene combinations) were obtained. The
ech42
gene
encoding for an endochitinase increased resistance to sheath blight caused
by
Rhizoctonia solani
, while the exochitinase-encoding gene,
nag70
, had
