Diverse responses of wild and cultivated tomato to BABA, oligandrin and Oidium neolycopersici infection.

Background and Aims: Current strategies for increased crop protection of susceptible tomato plants against pathogen infections include treatment with synthetic chemicals, application of natural pathogen-derived compounds or transfer of resistance genes from wild tomato species within breeding programmes. In this study, a series of 45 genes potentially involved in defence mechanisms was retrieved from the genome sequence of inbred reference tomato cultivar Solanum lycopersicum 'Heinz 1706'. The aim of the study was to analyse expression of these selected genes in wild and cultivated tomato plants contrasting in resistance to the biotrophic pathogen Oidium neolycopersici , the causative agent of powdery mildew. Plants were treated either solely with potential resistance inducers or by inducers together with the pathogen. Methods: The resistance against O. neolycopersici infection as well as RT-PCR-based analysis of gene expression in response to the oomycete elicitor oligandrin and chemical agent ß-aminobutyric acid (BABA) were investigated in the highly susceptible domesticated inbred genotype Solanum lycopersicum 'Amateur' and resistant wild genotype Solanum habrochaites . Key Results: Differences in basal expression levels of defensins, germins, ß-1,3-glucanases, heveins, chitinases, osmotins and PR1 proteins in non-infected and non-elicited plants were observed between the highly resistant and susceptible genotypes. Moreover, these defence genes showed an extensive up-regulation following O. neolycopersici infection in both genotypes. Application of BABA and elicitin induced expression of multiple defence-related transcripts and, through different mechanisms, enhanced resistance against powdery mildew in the susceptible tomato genotype. Conclusions: The results indicate that non-specific resistance in the resistant genotype S. habrochaites resulted from high basal levels of transcripts with proven roles in defence processes. In the susceptible genotype S. lycopersicum 'Amateur', oligandrin- and BABA-induced resistance involved different signalling pathways, with BABA-treated leaves displaying direct activation of the ethylene-dependent signalling pathway, in contrast to previously reported jasmonic acid-mediated signalling for elicitins.

Elicitin-membrane interaction is driven by a positive charge on the protein surface: role of Lys13 residue in lipids loading and resistance induction.

Elicitins are family of small proteins secreted by species of the pathogenic fungus Phytophthora inducing a defence reaction in plants. They contain a hydrophobic cavity capable of binding sterols and fatty acids, and on the basis of their pI they are classified as either α-elicitins or more necrotising ß-elicitins. The residue Lys13 was previously identified as a key determinant of the necrotising activity of basic elicitins. In the present study we describe changes in the ability of cryptogein, a ß-elicitin inducing a hypersensitive response in tobacco, to transfer sterols and fatty acids between micelles and liposomes upon Lys13Val mutation. We propose that the change in activity is influenced by the elimination of positive charge on the surface of cryptogein, which is significant for correct positioning of the protein during lipid loading, without adversely affecting the binding of sterol to the cavity of the protein. Compared to wild type cryptogein, mutation Lys13Val resulted in lowered expression of defence-related genes and compromised resistance to Phytophthora parasitica. Furthermore, resistance induced by Lys13Val mutant was similar to that induced by acidic elicitin capsicein containing at amino position 13 valine Determined results sustained a crucial role of positive lysine residues on the surface of basic elicitins and suggested their significant role in correct protein-membrane interaction and thus on their biological activity.