Cloning And Phylogenetic Analysis Of Sid-1 Genes From Aphids

The gene sid-1 encodes a transmembrane protein which is an important participator insystemic RNAi pathway. So far, sid-1 like genes are found in only tens of organismsdistributing among microbe, nematode, insect, fish and mammalian, but not in all oforganisms. Our work aligning C.elegans sid-1 amino acid sequence with all knownorganism genome on GenBank revealed that sid-1 homologous sequences present inHuman, mouse, rat, chimp, cow and dog, but not in sheep, pig or cat. In insects, it hasbeen reported that Schistocerca Americana, Apis mellifera, Bombyx mori and Triboliumcastaneum had 1-3 sid-1 like genes, but they were absent in the genome of Drosophilamelanogaster and Anopheles gambiae. It is obvious that detailed researchs on moreorganisms are needed to find distribution and evolution of sid-1 like genes.In this paper, degenerated PCR is used to clone sid-1 like gene in Aphidoidea and finallysid-1 like genes were found in three aphids, Aphis gossypii, Sitobion avenae andRhopalosiphum padi. The GenBank accession numbers are EF533711, EF533712,EF533713. With RACE strategy, the full length of the sid-1 gene from A. gossypii wasobtained, which is 2,301 bp in length encoding 766 amino acids. Sequence analysisindicated that the cloned gene share 25%, 38-42%, 32%-44%, 44% and 53% similaritywith its counterpart in C. elegans, B. mori, T. castaneum, A. mellifera and S. americana.A phylogenetic tree was generated using 23 amino acid sequences of sid-1 like genes from14 species of organism besides the three just cloned from aphids. Obviously, sid-1 genesexist from bacteria, nematode, echinus, insect, vertebrate to mammalian. Though theyshares lower similarity, which may proves that sid-1 genes have a long independentevolutional history, their sequence phylogenetic relations is well consistent with theirhost's evolution relations. These implies that sid-1 gene might be an ancient gene, andmight distribute in wide range of organisms.However, sid-1 like genes are not found in all of organisms. In mammals, they were foundto present in human, mouse, rat, chimp, cow and dog, but absent in the genome of sheep,pig and cat. In insects, they present in Schistocerca americana, A.mellifera, B.mori,T.castaneum, A.gossypii and S.avenae, but absent in the genome of D.melanogaster and A.gambiae. Though only a few species had been confirmed without sid-1 like genes, theycould be found to distribute random in animal kingdom. Thus, they were thought to losstheir sid-1 gene randomly during evolution, and they may have other compensatorypathways for its important founction, which should be further testified.