Abstract:
Conidia of the insect pathogenic fungus, Metarhizium anisopliae play an important role
in pathogenicity because they are the infective propagules that adhere to the surface of
the insect, then germinate and give rise to hyphal penetration of the insect cuticle.
Conidia are produced in the final stages of insect infection as the mycelia emerge from
the insect cadaver. The genes associated with conidiation have not yet been studied in
this fiingus. hi this study we used the PCR-based technique, suppression subtractive
hybridization (SSH) to selectively amplify conidial-associated genes in M. anisopliae.
We then identified the presence of these differentially expressed genes using the National
Center for Biotechnology Information database. One of the transcripts encoded an
extracellular subtilisin-like protease, Prl, which plays a fundamental role in cuticular
protein degradation. Analysis of the patterns of gene expression of the transcripts using
RT-PCR indicated that conidial-associated cDNAs are expressed during the development
of the mature conidium. RT-PCR analysis was also performed to examine in vivo
expression of Prl during infection of waxworm larvae {Galleria mellonelld). Results
showed expression of Prl as mycelia emerge and produce conidia on the surface of the
cadaver. It is well documented that Prl is produced during the initial stages of
transcuticular penetration by M. anisopliae. We suggest that upregulation of Prl is part
of the mechanism by which reverse (from inside to the outside of the host) transcuticular
penetration of the insect cuticle allows subsequent conidiation on the cadaver.
