| IntroductionInsect pest is one of major factors that cause yield reduction of crop, therefore, pest control is conducted through the process of agricultural practice. At the onset of 1950s, the 'green revolution' and the slogan 'better living through chemistry' shifted the pest control focus from a biocontrol approach to a chemical approach. However, the widely application of chemical pesticide has left the agriculture with pesticide resistance, agro-ecosystem collapse, environmental contamination and human health concerns. Under such circumstance, the biological strategy for pest control is receiving much attention.Compared with other microbial pathogens of insect, entomopathogenic fungi can invade host actively, and can infect pest circularly. Moreover, host can rarely develop resistance to entomopathogneic fungi. Therefore, mycoinsecticides are being considered as alternative and supplement to chemical pesticides. However, the acceptance of fungal products for pest control is very limited. What make limited acceptance of fungal insecticides is that they are not as fast acting as chemical products, sensitive to adverse environment, lose their effectiveness more rapidly. Therefore, entomoapathogenic fungal strain improvement is necessary. With the elucidation of molecular basis of fungal entomopathogenicity, gene engineering mightSummary overcome these drawbacks and could lead to an ideal biocontrol microorganism.Six integrated steps are involved in fungal pathogenesis in insect, and they are as following: 1) spore adhering to the cuticle of insect, 2) spore germination and infection structure formation, 3) penetration of host cuticle, 4) growth in host's hemocoel, 5) saprophytic feeding and host death and 6) hypha reemergence from inside host and sporulation on host cuticle. Penetrating host's cuticle is one of the key steps in infection. In common with phytopathogenic fungi, entry of insect fungi into the host also involves both mechanical pressure and enzymatic degradation. The complex refractory nature of insect cuticle suggests that penetration would require the synergistic action of several different enzymes including chitinase, protease and lipase. Among theses enzymes, subtilisin-like protease had been proved to play important role in the cuticle degradation in Metarhizium anisopliae. The constitutive expression of Prla was shown to enhance virulence of M. anisoplia greatly. Subtilisin-like protease gene had been found in several other entomopathogenic fungi, however, its role in the pathogenicity of these fungi remains to be established.Chitin accounts for 17%-50% of insect cuticle, and chitin synthesis-inhibited larvae of Maduca Sexta by Dimilin was more easily attacked by M. anisopliae, demonstrating that chitin was one of barriers that could protect insect from being invaded by foreign microorganisms. Therefore, It can be deduced that chitinases play important role in fungal pathogenesis in insect. However, overexpressing a chitinase gene CHII did not alter the virulence of M. anisopliae to the larvae of Maduca sexta, sggesting that this chitinase was not involved in cuticle degrading. Nevertheless, entomopahtogenic fungi, for example M. anisopliae, produced different kinds of chitinases in the process of penetrating host's cuticle, and the roles of these chitinases may be of difference, therefore, the general role of chitinases in fungal pathogenesis in insect remains to be further studied.In the medium using insect cuticle as sole carbon and nitrogen resource, chitinases were proved to act synergistically with proteolytic enzymes to degrade insect cuticle. As mentioned above, chitin-synthesis-inhibited larvae were easily attacked by M anisopliae. These two results made us think that proteases and chitinases may also act synergistically when entomopathogenic fungi penetrated insect cuticle. Therefore, we should investigate the role of chitinases in fungal pathogenesis in insect from the point of their interaction with proteasesBeauveria bassiana is a widely employed entomopa...
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