PR-10 proteins are a family of pathogenesis-related (PR) allergenic proteins playing multifunctional roles. The peach (Prunus persica) major allergen, Pru p 1.01, and its isoform, Pru p 1.06D, were found highly expressed in the fruit skin at the pit hardening stage, when fruits transiently lose their susceptibility to the fungal pathogen Monilinia spp. To investigate the possible role of the two Pru p 1 isoforms in plant defense, the recombinant proteins were expressed in Escherichia coli and purified. Light scattering experiments and circular dichroism spectroscopy showed that both proteins are monomers in solution with secondary structures typical of PR-10 proteins. Even though the proteins do not display direct antimicrobial activity, they both act as RNases, a function possibly related to defense. The RNase activity is different for the two proteins, and only that of Pru p 1.01 is affected in the presence of the cytokinin zeatin, suggesting a physiological correlation between Pru p 1.01 ligand binding and enzymatic activity. The binding of zeatin to Pru p 1.01 was evaluated using isothermal titration calorimetry, which provided information on the stoichiometry and on the thermodynamic parameters of the interaction. The structural architecture of Pru p 1.01 and Pru p 1.06D was obtained by homology modeling, and the differences in the binding pockets, possibly accounting for the observed difference in binding activity, were evaluated.

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Monilinia brown rot is one of the most important diseases of peach (Prunus persica L. Batsch). In this study, the susceptibility to Monilinia rot of peach fruit during ripening was analysed weekly by assessing infected fruits upon artificial inoculation. Fruit drastically reduced their susceptibility to Monilinia rot along with ripening, becoming resistant in correspondence to pit hardening (a two-week period). Susceptibility increases again thereafter. With the aim to identify genes possibly correlated with the variation of brown rot susceptibility, a microarray based-transcriptome analysis was undertaken to compare the expression of genes between susceptible fruit (two weeks before the pit hardening stage) and resistant fruit (at the pit hardening stage). This approach pointed out that genes involved in defence and primary and secondary metabolism, in particular some phenylpropanoid and flavonoid related genes, are differentially expressed in susceptible and resistant fruit. Considering that several aromatic compounds with antifungal properties are known to accumulate during endocarp lignification, the expression levels of genes encoding key enzymes of the phenylpropanoid and jasmonate pathways was quantified by real time RT-PCR in the peel of both susceptible and resistant fruit. Results show that during the two-week time between the susceptible and resistant fruit stages the expression of several genes involved in the synthesis of phenylpropanoid and jasmonate compounds drastically changes, supporting a role for these metabolites in the fruit response to Monilinia

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