Acta Horticulturae

Volatile organic compounds, most of them being terpenes, are signals emitted by plants for communication with the environment. Orange fruit accumulates mainly terpenes in mature peel oil glands with D-limonene accounting for approximately 97% of terpene content. We have generated transgenic orange plants carrying a D-limonene synthase gene in antisense (AS) configuration. Transgenic expression caused a dramatic decrease in the accumulation of D-limonene in fruit peels, being about 80-100 times lower in AS samples than in empty vector (EV) transgenic ones. This affected the interaction of fruits with their biotic environment because they resulted in resistance to different specialized pathogens. When antisense fruits were challenged with the fungus Penicillium digitatum, they showed marked resistance against this pathogen. A gene expression analysis of these fruits linked the decrease of D-limonene to upregulation of genes involved in the innate immunity response. High D-limonene content in mature orange peels may be a signal for attractiveness of microorganisms which might be likely involved in facilitating the access to the pulp of seed dispersal frugivores.