LAUSR

BACKGROUND Calcineurin is involved in numerous of cellular processes and Ca2+-dependent signal transduction pathways. With thousands of host larval (Spodoptera exigua) transcripts are downregulated after the infection of Heliothis virescens ascovirus 3h (HvAV-3h) in our previous transcriptome studies, the calcineurin encoded genes (SeCaNs) were highly upregulated. To understand the regulation of SeCaNs in S. exigua larvae during the infection of HvAV-3h, the function of calcineurin subunit A (SeCaN-SubA) and calcineurin binding protein (SeCaN-BP) were analyzed. RESULTS The in vitro assays indicated that the bacterial expressed PrSeCaN-SubA was an acid phosphatase, but no phosphatase activity was detected with the purified PrSeCaN-BP. The transcription level of SeCaN-SubA was upregulated after HvAV-3h infection and the calcineurin activity was significantly increased after HvAV-3h infection in S. exigua larvae. Interestingly, the SeCaN-BP transcripts were only detectable in the HvAV-3h infected larvae. Further immunoblotting results consistently agree with those obtained by qPCR which indicate that the infection of HvAV-3h caused the upregulated expression of SeCaN-SubA and the appearance of SeCaN-BP. An interaction between the cleaved SeCaN-SubA and SeCaN-BP was detected by co immunoprecipitation assays, and the expression of SeCaN-BP in Sf9 cells can help to increase the calcineurin activity of SeCaN-SubA. Further investigations with CaN inhibitors suggested that HvAV-3h stimulates host larval CaN activity enhance viral replication. CONCLUSION The increase of calcineurin activity caused by HvAV-3h infection might be due to the upregulation of SeCaN-SubA and the induced expression of SeCaN-BP, and the increased calcineurin activity is essential for the ascoviral replication. This article is protected by copyright. All rights reserved.