Juvenile hormone regulates an expression of a late gene encoded in a polydnavirus, Cotesia plutellae bracovirus

An endoparasitoid wasp Cotesia plutellae encodes two host translation inhibitory factors (HTIFs) that are expressed in late larval stage of Plutella xylostella parasitized by C. plutellae. The late expressions of HTIFs seemed to be associated with decreasing titer of juvenile hormone (JH) at the last larval instar because an addition of pyriproxyfen (PYR, a JH analog) inhibited the late expression pattern of two HTIF genes. To understand their late expression control, promoter region of an HTIF gene called CpBV15α was cloned by inverse PCR. The cloned HTIF upstream region (1113 bp) possessed a putative JH response element (JHRE) and other promoter elements. The putative promoter region was rejoined with an open reading frame of enhanced green fluorescence protein (EGFP). When the recombinant vector construct was injected into early third instar larvae of nonparasitized P. xylostella, it was expressed in fourth larval instar at 72 h after injection, compared to relatively early expression in 24 h after injection of control construct containing a baculovirus immediate-early promoter. However, recombinant EGFP construct lost the late expression pattern when its promoter region was incomplete by truncating JHRE region. PYR application inhibited EGFP expression of the recombinant construct, but gave little influence on truncated constructs. Interestingly, when the complete promoter construct was injected to pupal stage, its late expression pattern was lost and showed early expression pattern. However, an addition of PYR to pupae, which had been injected with the complete promoter construct, inhibited the reporter gene expression. These results suggest that late expression of a HTIF (CpBV15α) is controlled by its promoter, which is sensitive to host JH titer.