SBP-3264 Protocol zeaxanthin at the 7,eight(7 ,eight ) forming 3-hydroxy–cyclocitral and crocetin dialdehyde, the precursor for the formation of crocin and the spice saffron (Figure 8; see Section three.6.2) [139,245]. Ahrazem et al. [245] demonstrated that CsCCD2 requires a 3-hydroxy–ring and doesn’t Plants 2021, ten, x FOR PEER Evaluation 20 of 40 use -carotene or lycopene as a substrate. Crocetin dialdehyde has previously been shown to accumulate inside the flowers of Jacquinia angustifolia [246] and the roots of Coleus forskohlii [247].Figure eight. Scheme for the 7,8(7 ,8 reactions catalysed by the recombinant carotenoid cleavage deFigure 8. Scheme for the 7,8(7,8,),) reactions catalysed by the recombinant carotenoid cleavage oxygenases 2 2 Crocus sativus. deoxygenases inin Crocus sativus.A second novel carotenoid cleavage enzyme, the Zea maize CCD10a, cleaved neoxanA second novel carotenoid cleavage enzyme, the Zea maize CCD10a, cleaved neoxanthin,violaxanthin, antheraxanthin, lutein, zeaxanthin and -carotene in planta at five,six(5 ,6 ) thin, violaxanthin, antheraxanthin, lutein, zeaxanthin and -carotene in planta at 5,six(5,six) and 9,10(9,ten) positions, generating MHO (6-methyl-5-hepten-2-one) and also the 13 apocand 9,ten(9 ,ten ) positions, producing MHO (6-methyl-5-hepten-2-one) and also the CC13 apocarotenoids, geranylacetone, -ionone and -ionone [248]. ZmCCD10 over-expression arotenoids, geranylacetone, -ionone and -ionone [248]. ZmCCD10 over-expression and and down-regulation led to Cholesteryl sulfate Protocol alterations in expression of phosphate starvation response down-regulation led to alterations in thethe expression of phosphate starvationresponse regulators (PHR1) and phosphate transporters, whereas down-regulation of CCD10a regulators (PHR1) and phosphate transporters, whereas down-regulation of CCD10a made made plants susceptible to Pi deficiency, over-expression in Arabidopsis plant tolerance plants susceptible to Pi deficiency, over-expression in Arabidopsis enhanced enhanced plant to phosphatephosphate [248], further demonstrating that CCD-generated apocarotenoids tolerance to limitation limitation [248], further demonstrating that CCD-generated apohave vital regulatory functions in planta. Finally, WangFinally, Wang et reported have carotenoids have important regulatory functions in planta. et al. [201] have al. [201] that CCD10 is that CCD10 is located inplants only. As C13 apocarotenoids market arbuscular reported discovered in mycorrhizal mycorrhizal plants only. As C13 apocarotenoids promote mycorrhizalmycorrhizal symbiosis 3.six.2 [228,249,250]); [228,249,250]); over-expression of arbuscular symbiosis (See Section (See Section 3.six.two over-expression of CCD10 under low phosphate low phosphate increaseswhich may promote phosphate acquisition via the CCD10 under increases C13 formation, C13 formation, which might market phosphate acmycorrhiza fungal pathway (see [248]). quisition via the mycorrhiza fungal pathway (see [248]).3.five. Apocarotenoids Are Vital to Flavour and Aroma 3.five. Apocarotenoids Are Vital to Flavour and Aroma Terpenoid flavour volatiles are typically present in plants at reasonably low low levels, Terpenoid flavour volatiles are typically present in plants at somewhat levels, but possess strong powerful on the overallthe overall human of the flavour of [192,230,25156]. but possess effects effects on human appreciation appreciation in the flavour of these CDCs are viewed as to be amongst one of the most considerable contributors for the flavour [192,230,25156]. These CDCs are considere.