Biomedical Engineering Reference
In-Depth Information
C
HAPTER
17
Pathogenicity Genes in
Entomopathogenic Fungi
Used as Biopesticides
K. Uma Devi,*
Annette Reineke, G. Sandhya
and P. Akbar Ali Khan
Abstract
Entomopathogenic fungi are utilized as microbial pesticides against insect pests.
There is yet a large untapped potential of fungal based biopesticides. Information
of genes governing their pathogenicity and virulence can aid in their biotechnologi-
cal exploitation: both improvement of fungal strains for traits suitable for biopesti-
cide attributes and development of insect tolerant transgenic crops is likely. In the
last decade several molecular biology techniques have been employed to identify
genes regulating pathogenicity in entomopathogenic fungi. Fungal infection is
aggressive—fungi enter the insect host through the cuticle unlike other microbial
pests. Fungi thrive in the insect utilizing its nutrients and spread throughout its
body, secrete toxins due to which the insect is fi nally killed. Thus pathogenicity of
entomogenous fungi is governed by events before and after penetration into the
insect. Pre penetration events comprise of adhesion, sensing the insect, germina-
tion, appressorium formation which mechanically pushes the fungus through the
insect cuticle and various cuticle degrading enzymes like proteases, chitinases
and lipases. Post penetration affair involves evading the insect immune response,
utilization of the host nutrients, multiplication in the insect hemocoel and secretion
of toxins—the most prevalent among them being small cyclodepsipeptides—the
non ribosomal proteins. Subsequent to insect death the fungus emerges out of
the insect and grows on its surface and sporulates profusely. Some genes impli-
cated in most of these steps have been discovered. Many are yet to be unraveled.
An account of the pathogenicity genes reported so far in entomopathogenic
fungi is given. Fungi include cell wall protein genes which aid in adhesion, genes
