A non-venomous sPLA2 of a lepidopteran insect: Its physiological functions in development and immunity

Eicosanoids are oxygenated C20 polyunsaturated fatty acids that mediate various physiological processes in insects. Eicosanoid biosynthesis begins with a C20 precursor, arachidonic acid (5,8,11,14-eicosatetraenoic acid: AA). AA is usually released from phospholipids at sn-2 position by catalytic activity of phospholipase A(2) (PLA(2)). Although various PLA(2)s classified into 16 gene families ( = Groups) are known in various biological systems, few PLA(2)s are known in insects. Only two PLA(2)s involved in intracellular calcium independent PLA(2) (iPLA(2)) group have been identified in lepidopteran insects with well known eicosanoid physiology. This study reports the first secretory PLA(2) (sPLA(2)) in lepidopteran insects. A partial open reading frame (ORF) of PLA(2) was obtained by interrogating Spodoptera exigua transcriptome. Subsequent 3'-RACE resulted in a full ORF (Se-sPLA(2)A) encoding 194 amino acid sequence containing signal peptide, calcium-binding domain, and catalytic site. Phylogenetic analysis indicated that Se-sPLA(2)A was clustered with other Group III sPLA(2)s. Se-sPLA(2)A was expressed in most larval instars except late last instar. Its expression was inducible by immune challenge and juvenile hormone analog injection. RNA interference of Se-sPLA(2)A significantly suppressed cellular immunity and impaired larval development. These results suggest that non-venomous sPLA(2) plays a crucial role in immune and developmental processes in S. exigua, a lepidopteran insect.