Four plant defensins from an indigenous South African Brassicaceae species display divergent activities against two test pathogens despite high sequence similarity in the encoding genes

De Beer, Abre; Vivier, Melane A.

Four plant defensins from an indigenous South African Brassicaceae species display divergent activities against two test pathogens despite high sequence similarity in the encoding genes

dc.contributor.author	De Beer, Abre
dc.contributor.author	Vivier, Melane A.
dc.date.accessioned	2011-12-14T13:57:15Z
dc.date.available	2011-12-14T13:57:15Z
dc.date.issued	2011-10
dc.date.updated	2011-11-14T06:21:13Z
dc.description	The original publication is available at http://www.biomedcentral.com/1756-0500/4/459	en_ZA
dc.description	Publication of this article was funded by the Stellenbosch University Open Access Fund.
dc.description.abstract	Abstract Background Plant defensins are an important component of the innate defence system of plants where they form protective antimicrobial barriers between tissue types of plant organs as well as around seeds. These peptides also have other activities that are important for agricultural applications as well as the medical sector. Amongst the numerous plant peptides isolated from a variety of plant species, a significant number of promising defensins have been isolated from Brassicaceae species. Here we report on the isolation and characterization of four defensins from Heliophila coronopifolia, a native South African Brassicaceae species. Results Four defensin genes (Hc-AFP1-4) were isolated with a homology based PCR strategy. Analysis of the deduced amino acid sequences showed that the peptides were 72% similar and grouped closest to defensins isolated from other Brassicaceae species. The Hc-AFP1 and 3 peptides shared high homology (94%) and formed a unique grouping in the Brassicaceae defensins, whereas Hc-AFP2 and 4 formed a second homology grouping with defensins from Arabidopsis and Raphanus. Homology modelling showed that the few amino acids that differed between the four peptides had an effect on the surface properties of the defensins, specifically in the alpha-helix and the loop connecting the second and third beta-strands. These areas are implicated in determining differential activities of defensins. Comparing the activities after recombinant production of the peptides, Hc-AFP2 and 4 had IC50 values of 5-20 μg ml-1 against two test pathogens, whereas Hc-AFP1 and 3 were less active. The activity against Botrytis cinerea was associated with membrane permeabilization, hyper-branching, biomass reduction and even lytic activity. In contrast, only Hc-AFP2 and 4 caused membrane permeabilization and severe hyper-branching against the wilting pathogen Fusarium solani, while Hc-AFP1 and 3 had a mild morphogenetic effect on the fungus, without any indication of membrane activity. The peptides have a tissue-specific expression pattern since differential gene expression was observed in the native host. Hc-AFP1 and 3 expressed in mature leaves, stems and flowers, whereas Hc-AFP2 and 4 exclusively expressed in seedpods and seeds. Conclusions Two novel Brassicaceae defensin sequences were isolated amongst a group of four defensin encoding genes from the indigenous South African plant H. coronopifolia. All four peptides were active against two test pathogens, but displayed differential activities and modes of action. The expression patterns of the peptide encoding genes suggest a role in protecting either vegetative or reproductive structures in the native host against pathogen attack, or roles in unknown developmental and physiological processes in these tissues, as was shown with other defensins.	en_ZA
dc.description.version	Peer Reviewed	en_ZA
dc.format.extent	19 p. : ill.
dc.identifier.citation	De Beer, A. & Vivier, M. A. 2011. Four plant defensins from an indigenous South African Brassicaceae species display divergent activities against two test pathogens despite high sequence similarity in the encoding genes. BMC Research Notes. 4(1):459-478.	en_ZA
dc.identifier.issn	http://dx.doi.org/10.1186/1756-0500-4-459
dc.identifier.uri	http://hdl.handle.net/10019.1/18176
dc.language.iso	en_ZA	en_ZA
dc.language.rfc3066	en
dc.publisher	BioMed Central	en_ZA
dc.rights.holder	De Beer et al.; licensee BioMed Central Ltd.	en_ZA
dc.subject	Plants -- Disease resistance	en_ZA
dc.subject	Antimicrobial peptides	en_ZA
dc.subject	Brassicaceae species -- Plant defensins	en_ZA
dc.title	Four plant defensins from an indigenous South African Brassicaceae species display divergent activities against two test pathogens despite high sequence similarity in the encoding genes	en_ZA
dc.type	Article	en_ZA