Molecular and biochemical responses to wounding in

Postharvest Biology and Technology 90 (2014) 40–51

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Molecular and biochemical responses to wounding in mesocarp of ripe peach (Prunus persica L. Batsch) fruit Roberta Tosetti a , Francesca Tardelli b , Alice Tadiello c , Valerio Zaffalon d , Federico M. Giorgi e , Lucia Guidi b , Livio Trainotti c , Claudio Bonghi d , Pietro Tonutti a,∗ a

Institute of Life Science, Scuola Superiore Sant’Anna, 56127 Pisa, Italy Department of Agriculture, Food and Environment (DAFE), University of Pisa, 56100 Pisa, Italy c Department of Biology, University of Padova, 35121 Padova, Italy d Department of Agronomy, Food, Natural Resources, Animal and Environment, University of Padova, 35126 Legnaro, Padova, Italy e Center for Computational Biology and Bioinformatics, Columbia University, New York, 10032, USA b

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Article history: Received 15 September 2013 Accepted 1 December 2013 Keywords: Mechanical stress Microarray Minimally processing Postharvest physiology Secondary metabolism Transcription factors

a b s t r a c t The physiological and molecular responses of ripe fruit to wounding were evaluated in two peach (Prunus persica) varieties (‘Glohaven’, GH, melting and ‘BigTop’, BT, slow melting nectarine) by comparing mesocarp samples from wedges (as in minimal processing) and whole fruit as the control. Slight differences between the two varieties were detected in terms of ethylene production, whereas total phenol and flavonoid concentrations, and PPO and POD enzyme activities showed a general increase in wounded GH but not in BT. This was associated with the better appearance of the BT wedges at the end of the experimental period (72 h). Microarray (genome-wide ␮PEACH3.0) analysis revealed that a total number of 2218 genes were differentially expressed (p < 0.01, log2 fold change expression ratio >1 or 2 in GHw (Supplementary Table S4). This strongly supports the involvement of members of this TF superfamily in the response to wounding in peach mesocarp of the melting variety. Interestingly, an opposite behavior was observed in BT, where ten AP2/ERF genes appeared to be down-regulated (log2 FC 2). Changes in JA content in response to mechanical stress, and the possible relationship between JA (and its cross-talk with other hormones) and the expression of AP2/ERF members in response to wounding in fruit tissues would be interesting topics for future research. JA might also be implicated in the regulatory system controlled by TFs belonging to the WRKY family. A number of WRKY genes are induced by wounding treatments. In fact, in Nicotiana attenuata NaWRKY3 is strongly induced by wounding treatment and regulates expression of JA biosynthesis genes (LOX, AOS, AOC and OPR3) and JA conjugating genes, thereby increasing the levels of JA (Skibbe et al., 2008). This information along with the marked difference between GHw and BTw in terms of the expression pattern of WRKY (Fig. 5I) and AP2 (Fig. 5J) genes, would suggest a more complex mechanism involving WRKY and AP2 TFs together with JA in the response to wounding in fruit tissue. Perturbations in this mechanism might induce different responses, which could be the case of BT. An additional element supporting the hypothesis of JA involvement in the different responses to wounding in peach mesocarp is the up regulation of JAZ5 (ppa011370), a gene encoding jasmonate ZIM-domain (JAZ) repressor proteins (Ruiz et al., 2013) in GHw but not in BTw (Supplementary Table S4). In Arabidopsis JAZ gene expression is induced through a complex negative feedback loop mechanism in the presence of JA (Niu et al., 2011). Different responses to wounding between GH and BT are also represented by the expression pattern of genes encoding HSPs. In Arabidopsis, such genes play a wide role in many cellular processes, which may impart a generalized role in tolerance to multiple

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environmental stress conditions including wounding (Cheong et al., 2002). Indeed, a very high number of genes encoding HSPs (belonging to the stress abiotic·heat, and protein-folding BIN categories) were differentially expressed in both GH and BT but, again, a difference between the two varieties was observed at T2 sampling. In GH at least nine HSP genes were highly (log2 FC >2) up-regulated compared to the control, whereas in BT, using the same cut-off parameter (log2 FC >2/