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2.2.4. Genetic engineering o f PR-proteins
Constitutive expression of PR-proteins in transgenic plants have been reported
for increased resistance to pathogens. Increased tolcranca to
Pero~rosporn rtrt>aci~,a
and
Phyrophrhora parusifica
v:u.
r~icotiorr<rr
was demonstrated
in toh;\cco
overexpressing P R l a gene (Alexander
el a l . ,
1993). Transgenic rice and orange plants
overexpressing thaumatin-like PR-5 possessed increased tolerance to
Rhizoctorlia
.voluni
and
P. cirrophfhoru,
respectively (Datta
et u l . ,
1999; Fagoaga
er 01..
2001).
while transgenic potato overexpressing PR-2 and PR-3 had improved resistance to
P .
irfesrans
(Bachmann
et al.,
1998). PR-2 and PR-3 genes, coding for P-1,3-glucanase
and chitinase, respectively, confer resistance in carrot against several fungal
pathogens. The simultaneous expression of tobacco P-1.3-glucanase and chitinase
genes in tomato plants results in increased resistance to fungal pathogens (Melchers
et
al..
1998). Resistance is locally or systemically induced in plants when PR-proteins
are accumulated.
In tobacco, specific P-1,3-glucanases from alfalfa, barley, tobacco and
soybean have been shown to suppress fungal diseases (Bucher
ef a l . .
2001).
Overexpression of glucanases from soybean has been demonstrated to enhance
protection of potato from
P.
infestans
and kiwi from
B.
cinereu
(Grover and
Gowthaman, 2003). whereas a glucanase of potato was reported to increase resistance
in
flax
against
F.
oxysporum
and F.
culmorum
(Wrobel-Kwiatkowska
ef
al..
2004).
R. solani
was the first fungus shown to be suppressed in transgenic tobacco and
canola overexpressing a basic PR-3-type chitinase of bean (Grover and Gowthaman,
2003).
Chitinases
of
rice
were effective against
R. solani and Magnaporthe grisea
in
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