Insect Control: Biological and Synthetic Agents - Index of

436 A11: Addendum
Examination of gene expression patterns to understand
pathogenic and saprophytic adaptations of
various strains of entomopathogenic fungi was further
advanced by Wang et al (2009). They used
heterologous hybridization of genomic DNA from
specialist strains of Metarhizium to genes from the
generalist strain Ma2575. Approximately 7% of
Ma2575 genes were highly divergent or absent in
specialist strains. The absence of genes from the
specialist strains was taken as an indication of loss
of ability to utilize some substrates/environments.
These included genes involved in toxin biosynthesis
and sugar metabolism in root exudates, so the specialists
are losing genes required to live in alternative
hosts or as saprophytes.
Wang et al. (2005) identified M. anisopliae genes
which are upregulated in the presence of cuticle,
haemolymph, and root extract, providing more
insights into the variable habitats able to be colonized
by this entomopathogen. The demonstration
of specific genes which enable M. anisopliae to
adhere to insects (Mad1) and roots (Mad2) clearly
documented that the fungus has abilities as a rhizosphere
colonizer (Wang and St. Leger, 2007a).
Other studies have identified genes in addition
to those already mentioned, for example genes
encoding cuticle degrading enzymes (Fang et al.,
2005), a perilipin-like protein that regulates appressorium
turgor pressure and differentiation (Wang
and St. Leger, 2007b), sporulation-related genes
(Wu et al., 2008), and a G protein (Fang et al.,
2007, 2008).
Modification of entomopathogenic fungi to express
exotic proteins to improve performance has
been used successfully in Metarhizium and Beauveria.
The expression of scorpion neurotoxin AAIT
by transgenic strains of Metarhizium and Beauveria
led to a decrease in mean lethal concentration
(LC50) required to kill hosts. In M. anisopliae,
Wang and St Leger (2007c) placed AAIT under control
of a promoter which only expressed in the insect
haemolymph and found a 22-fold reduction of the
LC50 of the transgenic strain against Manducta
sexta and a 9-fold reduction against the mosquito,
Aedes aegypti. This strain was also effective against
the coleopteran coffee pest, Hypothenemus hampei
with the LC50 reduced 16-fold and survival time of
the pest reduced by 20% (Pava-Ripoll et al., 2008).
B. bassiana expressing AAIT and the cuticle degrading
protease Pr1A (from M. anisopliae) resulted in
transgenic strains that required less conidia to kill
host insects and a 40% reduction in the median
lethal time (Lu et al. 2008). A double transformant,
expressing both genes, was not more effective,
as it appears that the protease can degrade AAIT.
Similarly, Fan et al. (2007) overexpressed B. bassiana
chitinase and showed increased virulence
against the aphid, Myzus persicae. Similarly, Fang
et al. (2009) found that a mixture of a B. bassiana
protease Pr1A homolog (CDEP1) and a chitinase
Bbchit1 degraded insect cuticle in vitro more efficiently
than either CDEP1 or Bbchit1 alone. The
double transformant resulted in 60.5% reduction
in the LC50.
A11.9. Conclusion
It is clear that understanding the genetics, biology,
and ecology of entomopathogenic fungi is entering a
new era. New insights into the ecological roles these
fungi occupy have been strengthened by advances in
the ‘‘omics,’’ bringing perception on the genetics
underpinning substrate utilization and pathogenicity
determinants. The phylogenetic relationships between
the fungi are also becoming clearer, showing
new and interesting links to other fungal groups.
We may yet see entomopathogenic fungi fully live
up to their potential as widespread and versatile
control agents of invertebrate pests.
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