Gene expression analysis of peach fruit at different growth stages and with different susceptibility to Monilinia laxa

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.