Biomedical Engineering Reference
In-Depth Information
chitin, which is a homopolymer of 1,4-β-linked
N
-acetyl-D-glucosamine
(GlcNAc).
Trichoderma
species can inhibit the growth of other fungal
species by means of antibiotics and cell wall-degrading enzymes such as
chitinases, proteases, glucanases and mannanases.
Trichoderma
species are
specifi cally evolved to attack other fungi attributed chiefl y due to their
ability to produce highly effective chitinases. The 42-kDa endochitinase
produced by
Trichoderma
spp. is the most extensively studied chitinase
from biocontrol point of view. Different endochitinases, CHIT31, CHIT33,
CHIT36, CHIT37, CHIT42 and CHIT52, are produced by various strains of
T. harzianum
which differ in their molecular weight, p
I
value and structure
and are effective against a wide range of plant pathogenic fungi (Haran
et al. 1996, Viterbo et al. 2001, 2002, Markovich and Kononova, 2003).
CHIT36 is an endochitinase identifi ed in strain
T. harzianum
TM, which is
a 36-kDa protein belongs to the glycoside hydrolase family 18. Homology
studies showed that it has 79% nucleotide and 89% amino acid similarity
to CHIT37 from
T. harzianum
strain CECT 2413 but without signifi cant
similarity to other known
Trichoderma
endochitinases. Expression analysis
revealed that
chit36
gene is induced by conditions of stress, colloidal chitin
and
N
-acetyl-glucosamine. Interestingly, it was also demonstrated that
for the activation of the
chit36
promoter no direct contact of
T. harzianum
and a pathogen is required. Experiments with
T. harzianum
transformants
over-expressing the
chit36
gene regulated by a constitutive pki1 promoter
showed that the culture fi ltrate consisting of enzyme completely inhibited
germination of
B. cinerea
conidia. Moreover, the enzyme secreted to the
medium also signifi cantly reduced the growth of
Fusarium oxysporum
and
Sclerotium rolfsii
(Viterbo et al. 2001, 2002). In another experiment, Viterbo
et al. (2002) demonstrated that pure recombinant CHIT36 inhibited spore
germination of
A. alternata
,
B. cinerea
and
F. oxysporum.
The results of
these studies clearly demonstrated the role of the endochitinase CHIT36
in exhibiting antifungal activity
in vitro
by affecting development and
growth of pathogenic fungi. Similarly, carrot (
Daucus carota
subsp.
sativa
)
is a biennial plant grown worldwide for its edible taproot rich in pro-
vitamin A which is an excellent source of dietary fi bre. Reductions in
yield and quality in carrot is caused by a wide range of fungal pathogens
that infect the foliage and roots of carrot. Additionally, some of these
pathogens can also infect the roots during postharvest storage. Many
commercially-grown carrot cultivars lack adequate genetic resistance
to fungal pathogens, which is a serious constrain to carrot production
worldwide (Davis and Datnov 2002). Approaches involving genetic
engineering for increasing resistance to fungal pathogens have proved
successful in a number of agriculturally important crops, including
carrot (Melchers and Stuiver 2000, Punja 2001) and the most widely-used
approach is the over expression of the chitinase gene. Baranski et al. (2008)
