Distinct Responses of Thitarodes xiaojinensis β-1,3-Glucan Recognition Protein-1 and Immulectin-8 to Ophiocordyceps sinensis and Cordyceps militaris Infection

Abstract

Melanization and encapsulation are prominent defense responses against microbes detected by pattern recognition receptors of their host insects. In the ghost moth Thitarodes xiaojinensis, an activated immune system can melanize and encapsulate the fungus Cordyceps militaris. However, these responses were hardly detected in the host hemolymph postinfection of another fungus Ophiocordyceps sinensis. The immune interaction between O. sinensis and the host remains largely unknown, which hinders the artificial cultivation of Chinese cordyceps. We found that T. xiaojinensis b-1,3-glucan recognition protein-1 (bGRP1) was needed for prophenoloxidase activation induced by C. militaris. Failure of bGRP1 to recognize O. sinensis is a primary reason for the lack of melanization in the infected host. Lyticase or snailase treatment combined with binding and immunofluorescence detection showed the existence of a protective layer preventing the fungus from bGRP1 recognition. Coimmunoprecipitation and mass spectrometry analysis indicated that bGRP1 interacted with immulectin-8 (IML8) via binding to C. militaris. IML8 promotes encapsulation. This study suggests the roles of T. xiaojinensis bGRP1 and IML8 in modulating immune responses against C. militaris. Most importantly, the data indicate that O. sinensis may evade melanization by preventing bGRP1 recognition.

Transcriptome and Metabolome Analyses of Thitarodes xiaojinensis in Response to Ophiocordyceps sinensis Infection

“…This study indicated that the upregulated genes in Tx-BP were mainly confined to PGRPs and AMPs. Our previous study showed that a protective layer existed on the cell wall of Ophiocordyceps sinensis, avoiding βGPR1 induction [ 9 ]. Consistent with this finding, changes in βGPR1 expression were not detected in the fat body of Tx-BP.…”

“…The infection lasts at least 5 months until the host larvae are killed [ 8 ]. The unique development process of O. sinensis in ghost moth larvae and insect immunological responses during the early phase of infection (within several days) has been well described [ 7 , 8 , 9 ]. However, studies on the immune and metabolic changes of T. xiaojinensis during the long-term interaction between the host and O. sinensis are lacking.…”

“…Innate immunity constitutes a complex and interconnected network. It can protect insects from invasion by microbes, but it is not omnipotent [ 9 , 13 , 14 ]. Entomopathogenic fungi, such as Beauveria bassiana (Hypocreales: Cordycipitaceae) and Metarhizium anisopliae (Hypocreales: Clavicipitaceae), can integrate the strategies of nutrient deprivation, toxin production and inhibition of host immune responses to kill insects in as quickly as two weeks [ 15 , 16 , 17 ].…”

Immune functions of pattern recognition receptors in Lepidoptera

“…bGRPs not only play a recognition role in Lepidopterans to trigger the innate immune response but also act in synergy with other immunity to promote antifungal defense (104). bGRP1 in T. xiaojinensis interacts with immulectin-8 (a kind of lectin) to promote encapsulation of pathogens (105). Although the role of bGRPs in viral infection needs further research, bGRPs are considered to have antiviral potential.…”

Ophiocordyceps sinensis infection alters the immune system of the host Thitarodes xiaojinensis investigated by the interaction between immunity and gut microbiota escaping to hemolymph

“…It is worth mentioning that Cordyceps has a unique way of occurring and growing in the ecosystem, and unlike normal EPF that kill their hosts in a short period, it can co-grow with its hosts for a long period for as long as half a year to a year [9]. Currently, it is hypothesized that this result is due to the defense or tolerance of the host insect immune system against O. sinensis [9][10][11][12][13]. The mechanism of host immune response to O. sinensis remains unclear, when O. sinensis freely proliferates in hemolymph.…”