Biomedical Engineering Reference
In-Depth Information
evaluated the effect of CHIT36 in the transgenic carrot plants developed
that constitutively express the
T. harzianum
CHIT36 endochitinase and, for
the fi rst time, demonstrated that the microbial enzyme can enhance carrot
tolerance signifi cantly to three fungal phytopathogens namely
Alternaria
dauci
,
A. radicina
and
B. cinerea
.
A variety of other crops have also been engineered by using chitinase
genes from
Trichoderma
(Emani et al. 2003). Some of the crop species used
for transfer of the
Trichoderma
chitinase gene (Shah et al. 2010) are tobacco
and potato (Lorito et al. 1998), apple (Bolar et al. 2000, Bolar et al. 2001),
petunia (Esposito et al. 2000), grape (Kikkert et al. 2000) and broccoli (Mora
and Earle 2001). Transgenic tobacco and potato plants over expressing an
endochitinase (CHIT42) from
T. harzianum
have been shown to be highly
tolerant to the foliar pathogens
A. alternata
,
A. solani
and
B. cinerea
and also to
the deadly soil-borne pathogen
R. solani
(Lorito et al. 1998). Overexpression
of another endochitinase from
Trichoderma
(CHIT33) considerably enhances
the antifungal activity of
T. harzianum
strain CECT 2413 in
in vitro
confrontation experiments against
R. solani
. The amino acid sequence of
CHIT33 shows signifi cant similarity to some pathogenic response-associated
class III plant chitinases (Limo´n et al. 1995) but substantial biochemical
differences with other
Trichoderma
chitinases. Chitinases CHIT42 and
CHIT33 exhibit synergistic
in vitro
hydrolytic properties when assayed
against purifi ed fungal cell walls (de la Cruz et al. 1992). The production of
tobacco plants over expressing the
Trichoderma
endochitinase encoding gene
chit33
, alone or in combination with gene
chit42
, showed that overexpression
of
chit33
not only signifi cantly enhances their tolerance to fungal and
bacterial pathogens, but also their resistance to saline stress and high
concentrations of heavy metals. Although, the phenotype of the chitinase-
overexpressing plants is morphologically indistinguishable from that of
control lines with regard to biomass production, fertility, seed viability
and no synergistic effects of CHIT42 and CHIT33 have been observed in
planta. (Dana et al. 2006). However, in apple, high level expression of the
same endochitinase had been shown to have an adverse effect on plant
development. Interestingly, in one line with a low level of expression of
the endochitinase and with a moderate level expression of an exochitinase
gene, a high degree of resistance to apple scab was observed with normal
plant growth (Bolar et al. 2001). Genes encoding hydrolytic enzymes from
T. virens
have also been isolated in order to enhance mycoparasitism and
antifungal activities of biocontrol agents (Baek et al. 1999, Kim et al. 2002).
A diverse set of chitinase and glucanase genes were isolated by Kim et al.
(2002) from
T. virens
and their structural features and expression patterns
were characterized. Results from the study by Baek et al. (1999) suggested
that the transgenic expression of
T. virens
genes, encoding a 42 kDa class of
endochitinase enzymes, had a great potentiality to be utilized for enhancing
