Molecular Variability and Evolution of the Pectate Lyase (pel-2) Parasitism Gene in Cyst Nematodes Parasitizing Different Solanaceous Plants
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While pectate lyases are major parasitism factors in plant-parasitic nematodes, there is little information on the variability of these genes within species and their utility as pathotype or host range molecular markers. We have analysed polymorphisms of pectate lyase 2 (pel-2) gene, which degrades the unesterified polygalacturonate (pectate) of the host cell-wall, in the genus Globodera. Molecular variability of the pel-2 gene and the predicted protein was evaluated in populations of G. rostochiensis, G. pallida, G. “mexicana” and G. tabacum. Seventy eight pel-2 sequences were obtained and aligned. Point mutations were observed at 373 positions, 57% of these affect the coding part of the gene and produce 129 aa replacements. The observed polymorphism does not correlate either to the pathotypes proposed in potato cyst nematodes (PCN) or the subspecies described in tobacco cyst nematodes. The trees reveal a topology different from the admitted species topology as G. rostochiensis and G. pallida sequences are more similar to each other than to G. tabacum. Species-specific sites, potentially applicable for identification, and sites distinguishing PCN from tobacco cyst nematodes, were identified. As both G. rostochiensis and G. pallida display the same host range, but distinct from G. tabacum, which cannot parasitize potato plants, it is tempting to speculate that pel-2 genes polymorphism may be implicated in this adaptation, a view supported by the fact that no active pectate lyase 2 was found in G. “mexicana”, a close relative of G. pallida that is unable to develop on cultivated potato varieties.
KeywordsCell-wall degradation Globodera Parasitic factor Pectate lyase Plant-parasitic nematode Potato cyst nematode Convergent evolution Purifying selection
This work was supported by the Slovenian Research Agency and the Ministry of Agriculture, Forestry and Food of the Republic of Slovenia (V4-0324 and BI-FR/07-08-INRA-003) and INRA and the Ministry of higher Education, Science and Technology (MESST). This work benefited from link funded via COST 872 action. We would like to thank Dr. Didier Mugniery, Dr. Björn Niere and Dr. Nicola Greco for providing the G. rostochiensis populations and Dr. Matej Butala for advice on 3D modelling.
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