Characterization of a β-1,3-glucan recognition protein from the beet armyworm, Spodoptera exigua (Insecta: Lepidoptera: Noctuidae)

The -1,3-glucan recognition protein gene from Spodoptera exigua (SeGRP) was cloned and characterized. The cDNA of this gene is 1644 nucleotides in length and the predicted polypeptide is 491 amino acids (aa) in length, with a calculated molecular mass of 54.8 kDa. The first 22 aa encode a predicted secretion signal peptide. A BLAST search, multiple sequence alignment, and phylogenetic analysis of the aa sequence of SeGRP revealed that this protein is most similar to the -1,3-glucan recognition protein (GRP) family of pattern recognition proteins. Using reverse-transcription polymerase chain reaction, we detected the presence of SeGRP transcripts in the egg, larval, pupal, and adult stages of S. exigua. In addition, the SeGRP transcript was expressed in all the tissues examined including the brain, hemocytes, fat body, intestine, and cuticle. There were no changes in SeGRP mRNA levels in larvae infected with ultraviolet (UV)-killed Escherichia coli DH5 compared with the control larvae inoculated with the water; however, SeGRP mRNA levels were markedly elevated 4-8 h after infection and slightly induced 12-24 h after infection in larvae injected with UV-killed Fusarium oxysporum. This may be because -1,3-glucan is the main component of the cell wall of F. oxysporum, but not E. coli DH5.