ALTERATION OF ECDYSTEROID METABOLISM DUE TO BACULOVIRUS INFECTION OF THE FALL ARMYWORM SPODOPTERA-FRUGIPERDA - HOST ECDYSTEROIDS ARE CONJUGATED WITH GALACTOSE

The egt gene of the baculovirus Autographa californica nuclear polyhedrosis virus enables the virus to regulate the development of its infected host insect. This gene encodes an enzyme known as ecdysteroid UDP-glucosyltransferase that catalyzes the sugar conjugation of ecdysteroids. In this study, we have extended our characterization of this transferase and investigated the effects of virus infection on ecdysteroid metabolism in fall armyworm Spodoptera frugiperda (J. E. Smith) larvae. We show that the enzyme has a cleavable signal sequence at its amino-terminus and is rapidly secreted into the hemolymph of infected insects. In vitro studies indicate that ecdysteroid UDP-glucosyltransferase can catalyze both the glucose and galactose conjugation of ecdysteroids. Several lines of evidence indicate that, in vivo, the ecdysteroids are conjugated with galactose. Steady-state levels of ecdysteroids in the hemolymph of infected insects remain at low levels throughout infection.