Biomedical Engineering Reference
In-Depth Information
rodlets in the conidial surface. The hydrophobin-encoding
ssg
A gene in
M.
anisopliae
was found to be up regulated in response to nutrient deprivation
that induces responses similar to pre penetration stage of infection (St.
Leger et al. 1992b).The hydrophobins in
M. anisopliae
were found to be
similar to the hydrophobins of plant pathogenic fungi (Gao et al. 2011).
Different hydrophobins are synthesized by
M. anisopliae
in response to
different insect environments—cuticle
vs.
hemolymph (Freimoser et al.
2005). A regulator of the G protein signaling pathway was found to be
involved in conidiation and hydrophobin synthesis (Fang et al. 2007).
Lectins (carbohydrate binding glycoproteins) detected on the conidial
surface of
B. bassiana
have also been implicated in adhesion of conidia to
the insect cuticle (Boucias et al. 1988, Boucias and Pendland 1991). Two
cell wall proteins MAD1 (74.6 kD) and MAD2 (30.5 kD) have also been
implicated in adhesion (Wang and St. Leger 2007b). A mutation in these
genes greatly reduced virulence to insects due to delayed germination and
suppression of blastospore formation (Wang et al. 2005).The MAD1 protein
is synthesized in the spore during spore swelling prior to germination
and is therefore presumed to replace adhesins on the conidial surface
for stronger and specifi c interactions with the insect surface (Wang et al.
2005). The knocking-out of
Mad1
was found to down regulate several
genes, including a septin, involved in regulating the cytoskeleton and
cell cycle.
Mad1
infl uences organization of the cytoskeleton (Wang and
St. Leger 2007b). The disruption of
Mad2
blocked the adhesion of
M.
anisopliae
to plant epidermis but had no effects on fungal differentiation
and entomopathogenicity. The MAD1 and MAD2 proteins share similarity
with ALS (agglutinin-like sequence) cell wall protein of
Candida albicans
(Wang et al. 2005, Gao et al. 2011)
.
The ALS proteins are known to form
rapid and extremely stable H-bond-dependent associations with host
proteins and peptides. The MAD1 protein was found to have a predicted
glycosyl phosphatidyl inositol cell wall anchor site for signaling molecules
of cAMP pathway. In
B. bassiana
cultured on cuticle medium, an EST
homologous to a gene coding for dehydrogenase E1 component was
found (Khan et al. 2007). It is reported that this component is involved in
binding
Mycoplasma pneumoniae
(human pathogen) to fi bronectin, a very
common component of eukaryotic cell surfaces, basement membranes
and the extracellular matrix (Dallo et al. 2002).
Sensing the Insect Host Surface
The initial events of sensing the extracellular signals and transduction
into an intracellular signal are still poorly understood. The binding of
signal ligands to cell-surface receptors triggers a conformational change of
receptors, which activates kinases and transcription factors and proceeds
