Experiments were designed to investigate the molecular immune response of
Spodoptera littoralis larvae against bacterial infection. In addition, sequence and
phylogenetic analyses of the involved gene were studied. Using differential display
technique, a partial insect lectin gene (SpliLec) was isolated from bacterial-challenged
S. littoralis haemolymph. Five differentially displayed bands were sequenced.
Sequence results revealed that a fragment of 640 bp was amplified within the open
reading frame (orf) of a lectin gene. This fragment contained the complete 3` end with
a poly(A) tail, but it lacks start codon, AUG at its 5` end. Using RACE PCR reaction,
5` end was extended and a final reaction was performed to obtain the full length of the
SpliLec. Sequence analyses of the data revealed that SpliLec consists of a single orf
encoding a deduced polypeptide consisting of a 18-residue signal peptide and a 291-
residue mature peptide. SpliLec sequence contained two CRDs: short form CRD1 and
long form CRD2 stabilized by two and three highly conserved disulfide bonds,
respectively. SpliLec shares homology with some dipteran lectins suggesting possible
common ancestor. These results suggested an important role of the SpliLec gene in
cell adhesion and non-self recognition. It may cooperate with other AMPs in
clearance of invaders of Spodoptera littoralis.