LC–MS-Based Profiling Provides New Insights into Apocarotenoid Biosynthesis and Modifications in Citrus Fruits

Apocarotenoids contribute to fruit color and aroma, which are critical quality marketability attributes. Previously, we reported that the red peels of citrus fruits, characterized by higher expression levels a carotenoid cleavage dioxygenase 4b (CitCCD4b) gene, accumulate ?-citraurin ?-citraurinene than yellow peels. Here, identified quantified 12 apocarotenoids, either volatile or nonvolatile, in peel using liquid chromatography–mass spectrometry (LC–MS). Our results show contain also dramatically amounts ?-apo-8?-carotenal, crocetin dialdehyde known from saffron, ?-citraurol, ?-cyclocitral, 3-OH-?-cyclocitral up about 17-fold glucoside (picrocrocin isomer). The content these apocarotenoids was significantly increased different CitCCD4b-overexpressing transgenic callus lines, compared with corresponding controls. Transient CitCCD4b Nicotiana benthamiana leaves resulted striking increase level accumulation picrocrocin. Thus, our work reinforces specific function producing C10 apocarotenoid volatiles C30 pigments uncovers its involvement biosynthesis picrocrocin, C20 dialdehyde, alcohol suggesting potential this enzyme metabolic engineering their derivatives.