Amplifications of the greenbug (Schizaphis graminum) cDNA by semi-nested PCR resulted in two acetylcholinesterase (AChE, EC 3.1.1.7) DNA fragments with only 47% nucleotides identical in their corresponding regions. The first fragment deduced an amino acid sequence of 94 residues (AChE-1) that was closely related to AChE found in several insect species, whereas the second fragment deduced an 88-residue sequence (AChE-2) that was more related to nematode, human and other vertebrate AChEs. When these fragments were used as probes in Northern blot analysis of greenbug mRNA, AChE-1 and AChE-2 revealed transcripts of 7.6 and 3.7 kb, respectively. Screening of a greenbug cDNA library with the AChE-2 probe resulted in a full-length cDNA (3,285bp) that deduced an amino acid sequence of 581 residues for the mature protein. Phylogenetic analysis showed that greenbug AChE-2 formed a cluster with those of nematodes, ticks and a squid, and grouped out of the insect cluster, suggesting that the AChE-2 gene may evolve from a different duplicate gene lineage of insect AChEs. Our study has provided strong evidences of two distinctively different AChE genes in the greenbug, which is quite unique in contrast to only single AChE gene in vertebrates and many other insects.
Species 1: Homoptera Aphididae Schizaphis graminum (greenbug)
Keywords: Acetylcholinesterase, Molecular analysis
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