Effects of RNAi-mediated plasma membrane calcium transporting ATPase and inositol 1,4,5-trisphosphate receptor gene silencing on the susceptibility of Mythimna separata to wilforine.

Wilforine, a compound of sesquiterpene alkaloids isolated from Tripterygium wilfordii, exhibits excellent insecticidal activity against Mythimna separata. In order to clarify the action mechanism of wilforine, the plasma membrane calcium transporting ATPase (PMCA) and inositol 1,4,5-trisphosphate receptor (IPR) from M. separata were studied. Results showed that the open reading frame of MsIPR and MsPMCA were 8118 bp and 3438 bp in length, as well as encoded 2706 and 1146 amino acids, respectively. Multiple sequence alignment and phylogenetic analysis revealed that the MsIPR and MsPMCA had high homology with the IPR and PMCA of other insects, but had low similarity with those of mammals, which means the IPR and PMCA have potential to be the novel targets of insecticides with high selectivity between mammals and insects. Both MsIPR and MsPMCA genes existed throughout the life cycle of M. separata, and were all predominantly expressed in somatic muscle of fifth-instar larvae and the adults. The susceptibilities of PMCA-silenced M. separata to wilforine were significantly lower than that of the normal M. separata, which illustrates that PMCA could be one of the targets of wilforine. However, the susceptibilities of IPR-silenced M. separata to wilforine did not change significantly compared with the susceptibilities of normal M. separata, which shows that wilforine may not interact with the IPR protein. These findings provide clues for elucidating the insecticidal mechanism of wilforine.