Biomedical Engineering Reference
In-Depth Information
upregulation of specifi c genes. There is evidence of upregulation of
G-protein alpha subunit, phosphatidyl inositol-specifi c phospholipase
C, protein kinases, Ca/calmodulin dependent kinase and extracellular
signal-regulated protein kinases in
M. anisopliae
(Gao et al. 2011) and
B.
bassiana
(Khan et al. 2007) grown in medium with insect cuticle. It has
been reported that mitogen activated protein kinase pathway is strongly
activated during entomopathogenic fungal infection (Gao et al. 2011). G
protein alpha subunits have been extensively studied in fungi and many
are required for pathogenicity because fungi transduce extracellular signal
leading to infection specifi c development. The G-alpha genes—MAA-
03488 and MAC-04984 were found to be highly up regulated on cockroach
and locust cuticles (Gao et al. 2011).
Germination and Appressorium Formation
The host surface topography is suspected to infl uence appressorium
formation (St. Leger et al.
1991). Biochemical investigations indicated the
involvement of the intracellular second messengers Ca2+ and cyclic AMP
(cAMP) in appressorium formation (St. Leger et al.
1991). In
M. anisopliae,
a mutant for subunit of class 1 protein kinase—
MaPKA1
was found to
have delayed appressorium formation and the appressorium formed
was defective due to lack of turgor pressure (Fang et al. 2009). The
PKA
gene was found responsible for up regulating ~one-third of the genes
induced by insect cuticle including those responsible for differentiation
of appressoria and penetration pegs, degradation of cuticle, acquisition
of nutrients, regulation of pH, lipid synthesis, cell cycle control and the
cytoskeleton. It was concluded that
MaPKA1
gene is the key monitor of
the processes of sensing host-related stimuli and transduction of these
signals to regulate many infection processes (Fang et al. 2009). Many of
the PKA regulated genes in
M. anisopliae
are for secreted products (Fang
et al. 2009).
Zhang et al. (2010) report that mitogen activated protein kinases
(MAPKs) play a role both in appressorium formation and penetration of
the insect cuticle. MAP kinases belong to a family of serine—threonine
protein kinases which are crucial for transduction of extracellular signals
and development and differentiation of cell cycle process. Disruption of the
mitogen activated protein kinase gene
BbMPK1
was found to signifi cantly
decrease conidial adhesion to insect cuticles and eliminated their ability
to infect insects when applied topically to host insects but did not affect
growth of the fungus when conidia were injected directly into the hemocoel
(Zhang et al. 2010). However, the mutant fungus when injected into the
hemocoel could not colonize the surface of the insect cadaver. Therefore it
