Evolution of Phospholipase A2 in Bees and Flies

Phospholipase A2 (PLA2) as a component of venom has been studied intensively in venomous snakes while little has been done in insects. In this study, we firstly identified PLA2 among 36 Hymenoptera (Apis and Bombus genera) and 28 Diptera (Drosophila genus) by data mining on the known genomes. As a result, a total of 115 sequences were obtained, including 73 intact genes, 12 partial genes, and 30 pseudogenes. Most species have 1; 1 species from the Drosophila genus has 0, whereas both 1 species from the Drosophila genus and 9 species from the Bombus genus have two intact PLA2 genes. Secondly, 4 previously published intact PLA2 genes (1 from Apis, 2 from Bombus, and 1 from Drosophila) were added to the dataset of 73 intact genes and compared the evolutionary differences between the toxic group (Apis and Bombus genera) and non-toxic group (Drosophila genus) by conducting selective pressure analyses and protein structure prediction. The results showed that PLA2 from both Hymenoptera (Apis and Bombus genera) and Diptera (Drosophila genus) was under purifying selection. The evolutionary rate of the toxic group was larger than that of the non-toxic group; furthermore, PLA2 of Bombus species was subjected to accelerated evolution when compared with the other two groups. It may be attributed to the multiple venom injections of Bombus species, while in the Apis genus, the species has only one chance to inject, although both genera have stingers. In contrast, Drosophila has no stinger to inject and its PLA2 has other functions, which may link with development. This study lays the foundation for understanding the different roles of PLA2 in the genera Apis, Bombus, and Drosophila.