101 Early Jasmonate Application Interferes with Peach Fruit Development and Ripening as Revealed by Several Differentially Expressed Seed and Mesocarp Genes K.B. Ruiz, D. Bressanin, V. Ziosi, A. Tadiello and L. Trainotti G. Costa and P. Torrigiani Dipartimento di Biologia Dip. di Colture Arboree Università di Padova Università di Bologna Via Trieste 1, 35100 Padova Via Fanin 46, 40 127 Bologna Italy Italy C. Bonghi Dipartimento di Agronomia Ambientale e Produzioni Vegetali Università di Padova Viale dell’Università 16, 35020 Legnaro, Padova Italy Keywords: allene oxide synthase (AOS), ethylene-related genes, fruit ripening, I AD , methyl jasmonate, propyldihydrojasmonate, Prunus persica Abstract Peach (Prunus persica L. Batsch) was chosen to shed light on the physiological role of jasmonates (JAs) during fruit development and ripening. To this aim, the effects of methyl jasmonate (MJ, 0.80 mM) and propyl dihydrojasmonate (PDJ, 0.44 mM), applied in planta at the S1/S2 transition, on the time course of ethylene production and fruit quality traits, on gene expression of the first specific enzyme in the biosynthesis of jasmonic acid, allene oxide synthase (PpAOS1) and on the expression of some ethylene biosynthetic and perception genes were evaluated in the seed and mesocarp separately at harvest. Exogenously applied JAs affected ripening. Both compounds enhanced the transcription of PpAOS1 and down-regulated some ripening-related genes, such as 1-aminocyclopropane-1- carboxylic acid synthase (PpACS1) and 1-aminocyclopropane-1-carboxylic acid oxidase (PpACO1). MJ also altered the expression of the ethylene perception and signalling genes PpETR1, PpETR2 and PpERF2. Thus, in peach fruit, early application of MJ and PDJ led to a ripening delay due to a strong interference with ethylene-related gene expression in the seed and mesocarp of treated fruit at harvest. INTRODUCTION Jasmonic acid, its volatile ester methyl jasmonate (MJ), and other derivatives, collectively known as jasmonates (JAs), are ubiquitous signalling molecules which mediate plant responses to environmental stress (Reinbothe et al., 2009) and also play a role during developmental processes, including root growth, seed germination, pollen development fruit development and ripening (Peña-Cortés et al., 2005; Wasternack, 2007). Exogenous JAs cause dramatic transcriptional and phenotypical responses in most plant tissues (Rohwer and Erwin, 2008; Ziosi et al., 2008; Pauwels et al., 2009). In regard to ripening, that is a complex, genetically programmed process, in climacteric fruit progressive physicochemical and physiological changes are induced and, at least in part, co-ordinated by changes in ethylene biosynthesis and perception (Giovannoni, 2004). Studies on the role of ethylene during ripening of climacteric fruit have been carried out in several species (Cara and Giovannoni, 2008; Janssen et al., 2008). In this context, peach fruit is becoming a very promising climacteric drupe model as genes involved in ethylene biosynthetic and signal transduction pathways and ripening have been extensively characterized (Trainotti et al., 2006, 2007; Ziliotto et al., 2008). Peach fruit development is divided in four stages (S1, S2, S3 and S4): S1 is described as a result of high cell division and respiration rates; in S2 respiration decreases Proc. XI th IS on Plant Bioregulators in Fruit Production Ed.: G. Costa Acta Hort. 884, ISHS 2010