Biomedical Engineering Reference
In-Depth Information
These genes were induced only on the cuticle and most were up regulated
8- to 12-fold within 1 h when cultured on cuticle containing medium. Thus
genes required for catabolism of degradation products of cuticle proteins
are involved in fungal pathogenicity.
Chitinases
Chitinases have been reported to be pathogenicity determinants in
entomopathogenic fungi (Charnley and St. Leger 1991, St. Leger et
al. 1995, 1996a). The key role played by chitinases and lipases in the
process of infection has been demonstrated in
Nomuraea rileyi
(El-Sayed
et al. 1989, 1993). Overproduction of an endochitinase gene
Bbchit
was
demonstrated to signifi cantly enhance the virulence of
B. bassiana
(Fang
et al. 2005). An endochitinase gene
Vlchit1
from
Verticillium lecanii
has
been cloned and characterized for use in strain improvement (Zhu et al.
2008). In
M. anisopliae,
a chitinase gene was found to be expressed within
1 h after culture on cuticle containing medium (Freimoser et al. 2005,
Baratto et al. 2006). Some controversial experimental results have also
been reported with regard to the potential role of chitinases in infection
process. A chitinase defi cient mutant of
Verticillium lecanii
was still capable
of infecting aphids (Jackson et al. 1985).
An EST with similarity to DEAD/DEAH box helicase (an ATPase)
was detected in
B. bassiana
cultured on cuticle of
Aphis craccivora
(Khan et
al. 2007). This protein is implicated in important functions in mediating
pathogenesis in some fungi (Kim et al. 2000, Ribard et al. 2001).
GENES INVOLVED IN POST PENETRATION EVENTS
Colonization of the Hemocoel
After penetration of the cuticle and while switching to blastospore
stage in host hemolymph, the fungus produces osmosensors to protect
from the alkaline conditions of the hemolymph. Mos1 is one of the
osmosensors reported (Wang et al. 2008). After adapting to the hemocoel,
the fungus avoids activating the prophenoloxidase system (insect
defense mechanism) by turning off serine proteases (Wang et al. 2005).
The fungus while multiplying in the hemocoel produces several enzymes
and toxins.
Enzymes
In
M. anisopliae
,
acid phosphatase was found to play a key role in utilization
of organic phosphate for fungal growth in hemolymph which possibly
