Jasmonate-induced transcriptional changes suggest a negative interference with the ripening syndrome in peach fruit

Peach (Prunus persica L. Batsch) was chosen as a model to shed light on the physiological role of jasmonates (JAs) during fruit ripening. To this aim, the effects of methyl jasmonate (MJ, 0.40 mM) and propyl dihydrojasmonate (PDJ, 0.22 mM), applied in planta at different fruit developmental stages, on the time course of ethylene production and fruit quality traits were evaluated. MJ-induced changes in fruit transcriptome at harvest and the expression profiling of relevant JA-responsive genes were analyzed in control and JA-treated fruit. Exogenously applied JAs affected the onset of ripening depending upon fruit developmental stage with PDJ being more active than MJ. Both compounds enhanced the transcription of allene oxide synthase (PpAOS1), the first specific enzyme in the biosynthesis of jasmonic acid, and altered the pattern of jasmonic acid accumulation. Microarray transcriptome profiling showed that MJ down-regulated some ripening-related genes, such as 1-aminocyclopropane-1-carboxylic acid oxidase (PpACO1) and polygalacturonase (PG), and the transcriptional modulator IAA7. MJ also altered the expression of cell wall-related genes, namely pectate lyase (PL) and expansins (EXPs), and up-regulated several stress-related ones, including some of those involved in JA biosynthesis. Time course expression profiles of PpACO1, PL, PG, PpExp1 and of the transcription factor LIM confirmed array results. Thus, in peach fruit, exogenous JAs led to a ripening delay due to an interference with ripening- and stress/defence-related genes, as reflected on the transcriptome of treated fruit at harvest.