Rice Stripe Virus Infection Alters mRNA Levels of Sphingolipid-Metabolizing Enzymes and Sphingolipids Content in Laodelphax striatellus.

Sphingolipids and their metabolites have been implicated in viral infection and replication in mammal cells but how their metabolizing enzymes in the host are regulated by viruses remains largely unknown. Here we report the identification of 12 sphingolipid genes and their regulation by Rice stripe virus in the small brown planthopper (Laodelphax striatellus Fallén), a serious pest of rice throughout eastern Asia. According to protein sequence similarity, we identified 12 sphingolipid enzyme genes in L. striatellus. By comparing their mRNA levels in viruliferous versus nonviruliferous L. striatellus at different life stages by qPCR, we found that RSV infection upregulated six genes (LsCGT1, LsNAGA1, LsSGPP, LsSMPD4, LsSMS, and LsSPT) in most stages of L. striatellus Especially, four genes (LsCGT1, LsSMPD2, LsNAGA1, and LsSMS) and another three genes (LsNAGA1, LsSGPP, and LsSMS) were significantly upregulated in viruliferous third-instar and fourth-instar nymphs, respectively. HPLC-MS/MS results showed that RSV infection increased the levels of various ceramides, such as Cer18:0, Cer20:0, and Cer22:0 species, in third and fourth instar L. striatellus nymphs. Together, these results demonstrate that RSV infection alters the transcript levels of various sphingolipid enzymes and the contents of sphingolipids in L. striatellus, indicating that sphingolipids may be important for RSV infection or replication in L. striatellus.

A neutral ceramidase, NlnCDase, is involved in the stress responses of brown planthopper, Nilaparvata lugens (Stål).

Ceramidases (CDases) are vital enzymes involved in the biosynthesis of sphingolipids, which are essential components of eukaryotic membranes. The function of these enzymes in insects, however, is poorly understood. We identified a neutral ceramidase (NlnCDase) from the brown planthopper, Nilaparvata lugens, one of the most destructive hemipteran pests of rice. The C12-ceramide was the most preferred substrate for the NlnCDase enzyme. The activity of the NlnCDase enzyme was highest in the neutral-pH range (pH 6.0). It was inhibited by EGTA, Cs+ and Fe2+, while stimulated by EDTA and Ca2+. Moreover, the NlnCDase has higher transcript level and activity in adults than in eggs and nymphs, and in the reproductive organs (ovaries and spermaries) than in other tissues (i.e. heads, thorax, legs, midguts), which suggested that the NlnCDase might be elevated to mediate developmental process. In addition, transcripts and activity of the NlnCDase were up-regulated under abiotic stresses including starvation, abnormal temperature, and insecticides, and biotic stress of resistant rice varieties. Knocking down NlnCDase by RNA interference increased female survival under starvation and temperature stresses, suggesting that NlnCDase might be involved in the stress response in N. lugens.