Solanaceae Evolutionary Dynamics of the <i>I</i>2-NBS Domain

Abstract

In Solanaceae family several plant resistant genes to pathogen (R-genes) have been mapped and cloned. Most of them encode Nucleotide Binding Site Leucine Rich Repeat domain (NBS-LRR) protein. However, little is known about the resistance genes variability pattern and the evolutionary process acting on different species belonging to the same family. The aims of the present work, was to genotype and study the evolutionary relationship of fifty wild tomato accessions using the I2 resistance gene sequences. Thirty-three new candidate homologues I2 resistance gene nucleotide sequence were obtained from wild tomato species. Nucleotide polymorphisms in I2-NBS domain was detected in wild tomato species: diversity could have accumulated over a long time and species sorting could have produced new variants. In order to study the NBS-LRR domain variability we analyzed the evolution process acting on the amino acid sequence. The FEL method (codon Model) based on dN/dS, was used to estimate the presence of positive, negative and neutral selection acting on each codon. The I2-NBS domain sequence data studied seems to be under a general purification process of evolution. However, intermittent bouts of positive selection sites were detected in high variable regions. Phylogenetic analysis conducted within the Solanaceae family shows that the Solanum genus is under a rapid adaptative divergence process and Nicotiana and Capsicum clustered separately; Solanum peruvianum, in particular, displayed to be the most polymorphic specie. These results might be important for the identification of new sources of resistance genes to tomato pathogens.