Journal d'immunologie clinique et cellulaire
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Phylogeny of Host Response Proteins Activated in Silkworm Bombyx mori in Response to Infestation by Dipteran Endoparasitoid Revealed Functional Divergence and Temporal Molecular Adaptive Evolution

Pradeep AR, Anitha J, Panda A, Pooja M, Awasthi AK, Geetha NM, Ponnuvel KM and Trivedy K

Heterogeneous group of 19 host – response proteins were activated in commercially important silkworm, Bombyx mori after infestation by dipteran parasitoid, Exorista bombycis. The proteins include components of Toll and melanisation pathways, autophagy and apoptosis regulators, chaperones, cytokines and proteolytic enzymes. We elucidated phylogenetic relation within each host – response proteins belong to different insect orders. Multiple sequence alignment with most similar sequences showed large proportion of amino acid conservation in stress proteins, melanisation components, cactus, chitinase and autophagy 5 – like whereas signal proteins and cytokines showed ~30 % amino acid conservation. Phylogenetic analysis of the proteins revealed divergence which is an adaptive mechanism to provide immunity against parasitic attacks. In order to analyze phylogenetic position of the host – response proteins, amino acid sequences of all the proteins from B. mori and similar sequences from representative insects were aligned and constructed a phylogenetic tree based on maximum likelihood method using MEGA 5.05 program. Bootstrap values for Tree building method were obtained from 1000 replicates. The phylogenetic tree revealed three clusters. On the phylogenetic tree, cluster A showed early divergence of caspase and later divergence of BmToll whereas cluster B showed early divergence of prophenol oxidase activating enzyme (PPAE) through an independent lineage. PPAE expression showed pleiotropic correlation with different genes indicating initiation of diverse immune processes by PPAE at different time points in the evolutionary tree. NF κB transcription factors, dorsal and relish were diverged from common ancestor with high bootstrap value (83%) however showed 58% amino acid similarity. Relish showed long insertions revealing amino acid variations from dorsal. Cluster C illustrated divergence of autophagy 5- like, apoptosis - inducing factor and prophenol oxidase in temporal fashion to protect cells initially or to induce programmed cell death at later stages of parasitism.