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Molecular Plant Breeding 2012, Vol.3, No.7, 63-79
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70
involved in evading host immune responses (Wang
and St. Leger, 2006).
4 Entomopathogenic fungal virulence enzymes
The initial interaction in the pathogenesis is mediated
by mechanical force, enzymatic processes and perhaps
certain metabolic acids. The enzymes responsible for
successful interaction with the host and environment
are listed in Table 4 (Khachatourians and Qazi, 2008).
The enzymes involved in pathogenesis of insects are
generally grouped in to proteases and peptidases,
chitinases and lipases.
4.1 Proteases and peptidases
Insect cuticle mainly is composed of chitin and
protein; hence proteases and peptidases of EPF are
important for the degradation of the insect cuticle,
saprophytic growth of the fungi, activation of the
prophenol oxidase in the hemolymph, and they act as
virulence factor. The fungi from which protein degra-
ding enzymes proteases, collagenases, and chymolea-
stases have been identified and characterized are A.
aleyrodis, B. bassiana, B. brongniartii, E. coronata ,
Erynia spp., Lagenidium giganteum, Nomuraea rileyi,
M. anisopliae and V. lecanii (Charnley and St Leger
1991; Khachatourians, 1991, 1996; Sheng et al., 2006).
Joshi et al., (1995) cloned extracellular subtilisin-like
serine endoprotease (Pr1) from B. bassiana and
subtilisin-like protease (Pr1B) (Joshi et al., 1997) with
54% sequence homology to Pr1A. Screen and St Leger
(2000) found chymotrypsin (CHY1) of 374 amino acids
with pI of 5.07 and MW38279 from M. anisopliae.
Similarly, Freimoser et al (2005) identified some
overlapped gene responses with unique expression
patterns in response to cuticles from Lymantria dispar,
Blaberus giganteus and Popilla japonica and measured
gene expression responses to a number of insect
cuticles by using cDNA microarrays constructed from
an expressed sequence tags (EST) clone collection of
837 genes.
Small and Bidochka (2005) identified the sequence of
seven conidiation associated genes ( cag ) using
subtractive hybridization in M. anisopliae . Out of
which, cag7 was found to be essential for cuticle
degradat ion having encoded an extracel lular
subtilisin-like proteinase (Pr1). Kim et al (1999)
described the gene structure and expression of a novel
B. bassiana protease (bassianin I) which is 1 137 bp
and 379 amino acids long. Bidochka and Melzer
(2000) reported genetic polymorphisms in three
Table 4 Entomopathogenic fungal protein encoding genes isolated and sequenced (Khachatourians and Qazi, 2008)
Fungus Gene Enzyme References
Metarhizium anisopliae sod Superoxide dismutase Shrank et al., 1993
Pr1B Subtilisin like protease Joshi et al., 1997
Pr1 (A-K) Protease Bagga et al., 2004
CRR1 DNA binding protein Screen et al., 1997
nrr1 Nitrogen response regulator Screen et al., 1998
chit1 Chitinase Bogo et al., 1998
Chitinase Kang et al., 1998
Chitin synthase Nam et al., 1998
chi2 Chitinase Baratto et al., 2003; 2006; Screen et al., 2001
MeCPAA Zinc carboxypeptidase Joshi and St Leger, 1999
ssgA Hydrophobin Bidochka et al., 2001
Trehalase Zhao et al., 2006
Peptide synthetase Bailey et al., 1996
trp1 Tryptophan synthetase Staats et al., 2004
Beauveria bassiana prt1 Protease Joshi et al., 1995
Bassianin I Kim et al., 1999
prt1-like Serine endoprotease Fang et al., 2002
chit Chitinase Fang et al., 2005
Endonuclease Yokoyama et al., 2002
buv1 UV repair Chelico et al., 2006
B. brongniartii buv1 UV repair Chelico et al., 2006