Duplication and diversifying selection among termite antifungal peptides

Bulmer, Mark S., and Crozier, Ross H. (2004) Duplication and diversifying selection among termite antifungal peptides. Molecular Biology and Evolution, 21 (12). pp. 2256-2264.

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We have identified and analysed the mRNA sequence of 20 new defensin-like peptides from eleven Australian termite species of Nasutitermes and from an outgroup, Drepanotermes rubriceps. The sequence was amplified by reverse transcriptase PCR with a degenerate primer designed from termicin, an antifungal peptide previously characterized from the termite Pseudocanthotermes spiniger. All 20 genes show high sequence identity with P. spiniger termicin and have duplicated repeatedly during the radiation of Nasutitermes. Comparison of the relative fixation rates of synonymous (silent) and nonsynonymous (amino acid altering) mutations indicates that the Nasutitermes termicins are positively selected. This positive selection appears to drive a decrease in termicin charge. In termites with two genes, the decrease in charge is predominantly restricted to one termicin. Furthermore, the spread of charge is significantly greater within species than across species among sites that appear to be under strong positive selection and this spread is largely attributable to only three amino acids. Our results suggest that following termicin duplication, certain critical sites have maintained a positive charge in one duplicate and evolved towards neutrality in the other and that positive selection has directed these changes repeatedly and independently. This diversification among duplicated genes may be a counter-response to the evolution of fungal resistance in social insects that are particularly vulnerable to fungal epidemics.

Item ID: 277
Item Type: Article (Research - C1)
ISSN: 1537-1719
Keywords: Termites, Nasutitermes, Odontotermes, Tumulitermes, Host-parasite fungus, Immune-genes, Phylogeny immunogenes, Molecular-evolutionary-rates, dna-sequence, Termicin, Positive-selection
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Copyright © 2004 Society for Molecular Biology and Evolution. Published by Oxford University Press. The published version of this article can be accessed via Oxford Journals. Use hypertext links above.

Date Deposited: 11 Sep 2006
FoR Codes: 06 BIOLOGICAL SCIENCES > 0604 Genetics > 060409 Molecular Evolution @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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