Appressorial differentiation and its association with cAMP in the insect pathogenic fungus Metarhizium anisopliae
金龟子绿僵菌附着胞分化及其与环腺苷酸cAMP的关联性研究

Host recognition and appressorium differentiation are the pivotal steps for insect pathogenic fungi to initiate infection process. In this study, appressorial differentiation was studied by comparing a mutant, which has been identified with the loss of genetic materials, with the wild-type strain of the insect pathogenic fungus Metarhizium anisopliae. The observations showed that both the mutant and wild-type strain could not only produce appressoria on the tips of newly germinated spores, but also form multiple infection structures from the terminals of branching mycelia on insect cuticle. In contrast to the wild-type, the frequency of appressorial formation was significantly reduced and in addition, no clear mucilaginous sheath was produced by the mutant appressoria. The study shows that the cuticle degrading enzyme subtilisin is not involved in appressorial differentiation, or indispensable in cuticle digestion. A significantly low frequency of appressorial differentiation by the mutant was coincided with its lower intracellular cAMP level in comparison to the wild-type. Addition of exogenous cAMP could significantly increase the frequency of appressorial differentiation by the mutant, indicating that cAMP signaling pathway is potentially involved in regulation of appressorial differentiation in M. anisopliae.