ISOLATION AND FUNCTIONAL ANALYSIS OF McMenA, A GENE ENCODING A 1,4-DIHYDROXY-2-NAPHTHOATE OCTAPRENYLTRANSFERASE IN Mylabris cichorii.

Cantharidin is a biomolecule with a role in host defense that can also be used as an anticancer drug. The in vivo biosynthetic pathway for cantharidin has been the subject of debate for several decades and the mechanism is not yet completely understood. To study the biosynthetic pathway of cantharidin in blister beetles, Mylabris cichori, a full-length MenA (McMenA) cDNA was cloned based on the partial sequence of the MenA gene from a suppression subtractive hybridization (SSH) library of male and female adult M. cichorii. The cDNA was 1264 base pairs (bp) with an open reading frame of 1026 bp nucleotides encoding a 341 amino acid protein. Analysis of the McMenA amino acid sequence showed that the aspartate rich motif N/DDxxD represented binding sites for prenyl diphosphate via a Mg(2+) ion. Phylogenetic analysis showed that McMenA was most closely related to MenA of Tribolium castaneum, and the amino acid sequence similarity was 86%. The expression pattern of McMenA in adults was analyzed using RT-qPCR, and we found that the highest expression of McMenA occurred during 22-25 days in the sex-separate breeding males, while the lowest expression occurred in females at the same time. Injection with a specific double-strand RNA (dsRNA) of McMenA led to a significant reduction of McMenA mRNA levels after 24 h. Cantharidin and ATP concentrations dropped around the same time. Together, our data showed that the McMenA gene might be involved in cantharidin biosynthesis.