Effects of the fungal pathogen, Beauveria bassiana on protein biosynthesis of infected Spodoptera exigua larvae

Vegetative development of Beauveria bassiana in the hemocoel of the beet armyworm, Spodoptera exigua did not cause significant alterations in the profile of hemolymph proteins. Pulse-labeling tissue explants revealed that vegetative growth of B. bassiana hyphal bodies did not impact the biosynthetic capability of either the fat body or cuticle epidermis, both major sites of host protein synthesis. Even at the late stage of hyphal body development, when concentrations reached 3 x 10(4) fungal cells per mu l of hemolymph, both fat body and cuticle explants were capable of synthesizing and secreting the majority of proteins detected in naive samples. Hemocyte cultures were found to secrete significantly fewer labeled proteins than either fat body or cuticle explants. Replication of hyphal bodies in hemocyte cultures established from infected larvae induced the synthesis and secretion of 3 peptides having M(r) of 31, 32 and 40 kDa, Interestingly, peptides having identical M(r)s were detected in infected cell free hemolymph samples. These peptides did not correspond to proteins induced in response to heat shock suggesting that they may represent in vivo produced fungal metabolites. At the very late vegetative growth stage, the hyphal bodies produced germ tubes which invaded host tissues, Unlike the hyphal bodies, the mycelial tissue invasion phase inhibited host protein biosynthesis and produced a range of exocellular peptides.