(The) inducible immune genes against invading microorganisms in the fall webworm, Hyphantria cunea

Abstract

The inducible immune genes against invading microorganisms in the fall webworm, Hyphantria cunea, were studied. Eleven immune-related cDNA clones (Hdd1, Hdd2, Hdd3, Hdd8, Hdd11, Hdd13, Hdd15, Hdd17, Hdd23, Hs106 and Hs302) were isolated and characterized using PCR-based differential display (DD-PCR) and subtractive cloning methods. The deduced amino acid sequence of Hdd2 was shown to be a member of the copper, zinc superoxide dismutase (Cu-Zn SOD) family. The H. cunea Cu-Zn SOD is novel in that it is up-regulated following a bacterial challenge and has a putative signal peptide suggesting its secretion and involvement in the insect immune response. Hdd3 was found to encode a new member of the serpin serine protease inhibitor family. The H. cunea serpin may be involved in the prophenoloxidase cascade by modulating serine protease, which may cleave the maturation site of prophenoloxidase. The putative lectin corresponding to Hdd15 is novel among its class as it has two lectin C domains in a single molecule. These two lectin C domains show significant homology to the lectin C domain of Periplaneta lipopolysaccharide binding protein (LPS-BP). Three cloned genes, Hdd17, Hs106 and Hs302, encode homologues to Bombyx mori Gram negative bacteria binding protein, a hemolin-like protein and a attacin-like protein, respectively. The clone, Hdd8, was identical to the previously described H. cunea cecropin A3. On the contrary, Hdd1, Hdd11, Hdd13 and Hdd23 did not reveal any significant homology with known proteins. Only the deduced amino acid sequences from Hdd11 showed weak homology with a Locusta migratoria hemolymph protein. All of the 10 genes were clearly inducible by Escherichia coli and Micrococcus luteus injection. Injection of distilled water only slightly induced mRNA levels. Comparison of temporal mRNA expression following E. coli injection showed four types of expression patterns; rapid up-regulation followed by rapid down regulation (SOD, serpin, lectin, GNBP, h...