Identification of Genes Differentially Expressed by Metarhizium anisopliae Growing on Locusta migratoria Wings Using Suppression Subtractive Hybridization

Differential expression of the pr1A gene in Metarhizium anisopliae and Metarhizium acridum across different culture conditions and during pathogenesis

The entomopathogenic fungi of the genus Metarhizium have several subtilisin-like proteases that are involved in pathogenesis and these have been used to investigate genes that are differentially expressed in response to different growth conditions. The identification and characterization of these proteases can provide insight into how the fungus is capable of infecting a wide variety of insects and adapt to different substrates. In addition, the pr1A gene has been used for the genetic improvement of strains used in pest control. In this study we used quantitative RT-PCR to assess the relative expression levels of the pr1A gene in M. anisopliae and M. acridum during growth in different culture conditions and during infection of the sugar cane borer, Diatraea saccharalis Fabricius. We also carried out a pathogenicity test to assess the virulence of both species against D. saccharalis and correlated the results with the pattern of pr1A gene expression. This analysis revealed that, in both species, the pr1A gene was differentially expressed under the growth conditions studied and during the pathogenic process. M. anisopliae showed higher expression of pr1A in all conditions examined, when compared to M. acridum. Furthermore, M. anisopliae showed a greater potential to control D. saccharalis. Taken together, our results suggest that these species have developed different strategies to adapt to different growing conditions.

Fas-associated factor 1 plays a negative regulatory role in the antibacterial immunity of Locusta migratoria

Insect immune responses are precisely regulated to maintain immune balance. In this study, the Fas-associated factor 1 (FAF1) gene of Locusta migratoria manilensis, a homologue of the caspar gene that functions as a specific negative regulator in the antibacterial immunity pathway, was cloned. Gene expression analysis showed that FAF1 was expressed throughout the developmental stages and in all tested tissues, but its transcription levels varied significantly. Thus, FAF1 appears to be tightly regulated and is probably involved in multiple physiological processes. In addition, the antimicrobial peptide gene prolixicin was cloned and characterized. After bacterial challenge, prolixicin was rapidly up-regulated, whereas FAF1 was markedly down-regulated. This result was consistent with the observation that prolixicin was hyperactivated when FAF1 was suppressed by RNA interference. Moreover, after bacterial infection, the survival rate of FAF1-knockdown locusts was much higher than that of the wild-type. Taken together, these findings strongly suggest that FAF1 shares a similar function as caspar in Drosophila and may be involved in the negative regulation of antibacterial immunity in locusts.