Wounding tomato fruit elicits ripening-stage specific changes in gene expression and production of volatile compounds.

Valentina Baldassarre,Alessio Aprile,Hilary J Rogers,Giovanni Cabassi,Carsten T Müller,Antonio Ferrante,Natasha D Spadafora

doi:10.1093/jxb/eru516

Abstract

Fleshy fruits develop from an unripe organ that needs to be protected from damage to a ripe organ that attracts frugivores for seed dispersal through production of volatile organic compounds (VOCs). Thus, different responses to wounding damage are predicted. The aim of this study was to discover whether wound-induced changes in the transcriptome and VOC production alter as tomato transitions from unripe to ripe. Transcript changes were analysed 3h post-wounding using microarray analysis in two commercial salad-tomato (Solanum lycopersicum L.) cultivars: Luna Rossa and AVG, chosen for their high aroma production. This was followed by quantitative PCR on Luna Rossa genes involved in VOC biosynthesis and defence responses. VOCs elicited by wounding at different ripening stages were analysed by solid phase micro extraction and gas chromatography-mass spectrometry. Approximately 4000 differentially expressed genes were identified in the cultivar AVG and 2500 in Luna Rossa. In both cultivars the majority of genes were up-regulated and the most affected pathways were metabolism of terpenes, carotenoids, and lipids. Defence-related genes were mostly up-regulated in immature stages of development, whereas expression of genes related to VOCs changed at riper stages. More than 40 VOCs were detected and profiles changed with ripening stage. Thus, both transcriptome and VOC profiles elicited by wounding depend on stage of ripening, indicating a shift from defence to attraction.

Highlights

Fruits are important organs in which seed formation takes place and which become vehicles for conserving all the genome information spatially and temporally
Samples were separated on a 30 m × 0.25 mm internal diameter × 0.25 μm DB5 column (FactorFour, Varian) using the following temperature profile: initial temperature of 50 °C with a linear increase of 5 °C min–1 to 140 °C and a linear increase of 15 °C min–1 to 300 °C followed by 2 min at 300 °C
Identity of compounds was further verified by comparing mass spectra to those of pure compounds tested on the same gas chromatograph (GC)-MS machine using identical settings, as co-injection is not possible when using solid-phase microextraction (SPME) fibres

Summary

Introduction

Fruits are important organs in which seed formation takes place and which become vehicles for conserving all the genome information spatially and temporally. In pigments, sugars, and cell wall composition (Schaefer, 2011; Giovannoni et al, 2004, 2007; Klee and Giovannoni, 2011) These result in changes in fruit colour, a reduction in bitter flavour, fruit softening, which helps to release the seeds, and the production of flavour-associated compounds the most important of which are sugars, acids, and volatile organic compounds (VOCs). These changes have direct horticultural implications for post-harvest management and consumer appeal. Given the different ecological roles of fruit at the unripe and ripe stages here it was investigated whether wounding/slicing at different stages elicits distinct responses

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