Silencing Phytoene Desaturase Causes Alteration in Monoterpene Volatiles Belonging to the Methylerythritol Phosphate Pathway.

Volatile organic compounds (VOCs) are a large group of lipophilic hydrocarbon compounds derived from different biosynthetic pathways in plants. VOCs are produced and released from plants as a defense mechanism against biotic and abiotic stresses. They are involved in communication with the surrounding environment including plant-to-plant interactions and attracting or repelling insects. In citrus, phytoene desaturase (PDS), a precursor of the carotenoid biosynthetic pathway has been silenced using the Citrus tristeza virus -induced gene silencing technique. Silencing PDS resulted in a reduction of carotenoid contents and in the photobleaching phenotype in leaves. Interestingly, the strength of the phenotype was varied within the plants due to the unequal distribution of virus particles. Using solid-phase microextraction (SPME), fibers released VOCs from leaves with gradient degrees of the photobleaching phenotype were collected and analyzed in gas chromatography-mass spectrophotometry (GC-MS). Overall, 47 VOCs belonging to 12 chemically distinguished groups were detected and identified using authentic standards. Simple linear regression showed that monoterpenes belonging to methylerythritol phosphate (MEP) were significantly corrected with the degrees of photobleaching (carotenoid content). Both carotenoids and MEP biosynthetic pathways occurred in the plastid. Thus, we provide preliminary evidence for a potential role of carotenoids in supporting the MEP pathway and/or the production of monoterpenes.