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Open Access Research article

Evolutionary patterns at the RNase based gametophytic self - incompatibility system in two divergent Rosaceae groups (Maloideae and Prunus)

Jorge Vieira1, Pedro G Ferreira12, Bruno Aguiar1, Nuno A Fonseca3 and Cristina P Vieira1*

Author Affiliations

1 Instituto de Biologia Molecular e Celular (IBMC); University of Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal

2 Centre for Genomic Regulation; C/Dr. Aiguader, 88; 08003 Barcelona, Spain

3 CRACS-INESC Porto, Rua do Campo Alegre 1021/1055, 4169-007 Porto, Portugal

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BMC Evolutionary Biology 2010, 10:200  doi:10.1186/1471-2148-10-200

Published: 28 June 2010

Abstract

Background

Within Rosaceae, the RNase based gametophytic self-incompatibility (GSI) system has been studied at the molecular level in Maloideae and Prunus species that have been diverging for, at least, 32 million years. In order to understand RNase based GSI evolution within this family, comparative studies must be performed, using similar methodologies.

Result

It is here shown that many features are shared between the two species groups such as levels of recombination at the S-RNase (the S-pistil component) gene, and the rate at which new specificities arise. Nevertheless, important differences are found regarding the number of ancestral lineages and the degree of specificity sharing between closely related species. In Maloideae, about 17% of the amino acid positions at the S-RNase protein are found to be positively selected, and they occupy about 30% of the exposed protein surface. Positively selected amino acid sites are shown to be located on either side of the active site cleft, an observation that is compatible with current models of specificity determination. At positively selected amino acid sites, non-conservative changes are almost as frequent as conservative changes. There is no evidence that at these sites the most drastic amino acid changes may be more strongly selected.

Conclusions

Many similarities are found between the GSI system of Prunus and Maloideae that are compatible with the single origin hypothesis for RNase based GSI. The presence of common features such as the location of positively selected amino acid sites and lysine residues that may be important for ubiquitylation, raise a number of issues that, in principle, can be experimentally addressed in Maloideae. Nevertheless, there are also many important differences between the two Rosaceae GSI systems. How such features changed during evolution remains a puzzling issue.