Submitted to: Journal of Molecular Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 31, 2005
Publication Date: May 25, 2006
Citation: Shatters, R.G., Boykin, L.M., Lapointe, S.L., Hunter, W.B., Weathersbee III, A.A. 2006. Phylogenetic and structural relationships of PR-5 gene family reveals an ancient multigene family conserved in plants and select animal taxa. Journal of Molecular Evolution. 63(1):12-29. Interpretive Summary: The presence and great diversity of antimicrobial proteins in insects and other living organisms have recently been discovered. Using these as a weapon against insect vectored plant diseases offers hope in developing control strategies that are both environmentally friendly and of little risk to human health. This paper presents the discovery of a class of antimicrobial peptides in diverse insect species and presents the relationship of sequence and structure in these proteins among plants and animals in which related proteins are found. This data will be useful in determining protein characteristics that confer functional specificities (i.e. mode of action and pathogen specificity). Ultimately this information will be used to identify or design specific antimicrobial peptides to target specific important pathogens.
Technical Abstract: Pathogenesis-related group 5 (PR-5) plant proteins includes thaumatin, osmotin and related proteins, many of which have antimicrobial activity. Recent discovery of PR-5-like (PR-5L) sequences in nematodes and insects raises questions about their evolutionary relationships. Using complete plant genome data and discovery of multiple insect PR-5L sequences, phylogenetic comparisons among plants and animals were performed. All PR-5/PR-5L protein sequences were mined from genome data of a member of each of two main angiosperm groups: the eudicots (Arabidoposis thaliana) and the monocots (Oryza sativa), and from the Caenorhabditis nematode (C. elegans and C. briggsase). Insect PR-5L sequences were mined from EST databases and GenBank submissions from four insect orders: Coleoptera (Diaprepes abbreviatus and Biphyllus lunatus), Orthoptera (Schistocerca gregaria), Hymenoptera (Lysiphlebus testaceipes), and Hemiptera (Toxoptera citricida). Parsimony and Bayesian phylogenetic analyses showed the PR-5 family is paraphyletic in plants, likely arising from ten genes in a common ancestor to monocots and eudicots. After evolutionary divergence of monocots and eudicots, PR-5 genes increased asymmetrically among the 10 clades. Insects and nematodes contain multiple sequences (seven PR-5Ls in nematodes and at least three in some insects) all related to the same plant clade, with nematode and insect sequences separating as two clades. Protein structural homology modeling showed strong similarity among animal and plant PR-5/PR-5Ls with divergence only in surface-exposed loops. Sequence and structural conservation among PR-5/PR-5Ls suggests an important and conserved role throughout evolutionary divergence of the diverse organisms from which they reside.