XBP1 and ATF4 inhibit WSSV replication and promote host survival by modulating Spatzle expression in Macrobrachium nipponense.

X-box binding protein 1 (XBP1) and activating transcription factor 4 (ATF4) are transcription factors involved in the unfolded protein response (UPR) signaling pathway and have been reported to play important roles during viral infection in shrimp. To further investigate their functions during white spot syndrome virus (WSSV) infection in the prawn Macrobrachium nipponense, we cloned and characterized the full-length cDNA sequences of MnXBP1 and MnATF4. The MnXBP1 protein contains a basic leucine zipper (bZIP) domain and a low-complexity region, while MnATF4 possesses two internal repeats, a bZIP domain, and five low-complexity regions. RT-qPCR analysis revealed that both MnXBP1 and MnATF4 were widely expressed in various tissues, with the highest expression levels observed in the hepatopancreas. Following WSSV challenge, the expression of both genes was upregulated in the stomach and intestine at specific time points. In MnXBP1 or MnATF4 knockdown prawns with WSSV challenge, the expression levels of five different Spatzle (MnSpz) genes were significantly reduced, whereas the expression of the viral envelope protein VP28 was increased. Furthermore, knockdown of MnXBP1 or MnATF4 resulted in elevated WSSV copy numbers and a marked reduction in the survival rate of M. nipponense. Taken together, these findings suggest that MnXBP1 and MnATF4 exert antiviral effects against WSSV and may suppress viral replication by regulating the expression of MnSpz genes, which are key components of the Toll signaling pathway.