Peach (Prunuspersica L. Batsch) was

Peach (Prunuspersica L. Batsch) was chosen asa model to shed light on the physiological role ofjasmonates (JAs) during fruit ripening. To this aim, theeffects of methyl jasmonate (MJ, 0.40 mM) and propyldihydrojasmonate (PDJ, 0.22 mM), applied in planta atdifferent fruit developmental stages, on the timecourseof ethylene production and fruit quality traitswere evaluated. MJ-induced changes in fruit transcriptomeat harvest and the expression profiling ofrelevant JA-responsive genes were analysed in controland JA-treated fruit. Exogenously applied JAs affectedthe onset of ripening depending upon the fruit developmentalstage, with PDJ being more active thanMJ. Both compounds enhanced the transcription ofallene oxide synthase (PpAOS1), the first specificenzyme in the biosynthesis of jasmonic acid, andaltered the pattern of jasmonic acid accumulation.Microarray transcriptome profiling showed that MJdown-regulated some ripening-related genes, such as1-aminocyclopropane-1-carboxylic acid oxidase(PpACO1) and polygalacturonase (PG), and the transcriptionalmodulator IAA7. MJ also altered the expressionof cell wall-related genes, namely pectatelyase(PL) and expansins (EXPs), and up-regulated severalstress-related genes, including some of those involvedin JA biosynthesis. Time-course expression profiles ofPpACO1, PL, PG, PpExp1, and the transcription factorLIM confirmed the array results. Thus, in peach fruit,exogenous JAs led to a ripening delay due to aninterference with ripening- and stress/defence-relatedgenes, as reflected in the transcriptome of treated fruitat harvest