CcD1

Provitamin-A (proA) is essentially required for vision in humans but its deficiency affects children and pregnant women especially in the developing world. Biofortified maize rich in proA provides new opportunity for sustainable and cost-effective solution to alleviate malnutrition, however, significant loss of carotenoids during storage reduces its efficacy. Here, we studied the role of carotenoid cleavage dioxygenase 1 (ccd1) gene on degradation of carotenoids in maize. A set of 24 maize inbreds was analyzed for retention of proA during storage. At harvest, crtRB1-based maize inbreds possessed significantly high proA (β-carotene: 12.30 µg/g, β-cryptoxanthin: 4.36 µg/g) than the traditional inbreds (β-carotene: 1.74 µg/g, β-cryptoxanthin: 1.28 µg/g). However, crtRB1-based inbreds experienced significant degradation of proA carotenoids (β-carotene: 20%, β-cryptoxanthin: 32% retention) following 5 months. Among the crtRB1-based genotypes, V335PV had the lowest retention of proA (β-carotene: 1.63 µg/g, β-cryptoxanthin: 0.82 µg/g), while HKI161PV had the highest retention of proA (β-carotene: 4.17 µg/g, β-cryptoxanthin: 2.32 µg/g). Periodical analysis revealed that ~ 60-70% of proA degraded during the first three months. Expression analysis revealed that high expression of ccd1 led to low retention of proA carotenoids in V335PV, whereas proA retention in HKI161PV was higher due to lower expression. Highest expression of ccd1 was observed during first 3 months of storage. Copy number of ccd1 gene varied among yellow maize (1-6 copies) and white maize (7-35 copies) while wild relatives contained 1-4 copies of ccd1 gene per genome. However, copy number of ccd1 gene did not exhibit any correlation with proA carotenoids. We concluded that lower expression of ccd1 gene increased the retention of proA during storage in maize. Favourable allele of ccd1 can be introgressed into elite maize inbreds for higher retention of proA during storage.

Olfactory cues are key drivers of our multisensory experiences of food and drink. For example, our perception and enjoyment of the flavour and taste of a wine is primarily steered by its aroma. Making sense of the underlying smells that drive consumer preferences is integral to product innovation as a vital source of competitive advantage in the marketplace, which explains the intense interest in the olfactory component of flavour and the sensory significance of individual compounds, such as one of the most important apocarotenoids for the bouquet of wine, β-ionone (violet and woody notes). β-Ionone is formed directly from β-carotene as a by-product of the actions of carotenoid cleavage dioxygenases (CCDs). The biological production of CCDs in microbial cell factories is one way that important aroma compounds can be generated on a large scale and with reduced costs, while retaining the 'natural' moniker. The CCD family includes the CCD1, CCD2, CCD4, CCD7 and CCD8; however, the functions, co-dependency and interactions of these CCDs remain to be fully elucidated. Here, we review the classification, actions and biotechnology of CCDs, particularly CCD1 and its action on β-carotene to produce the aromatic apocarotenoid β-ionone.

Oxidative tailoring of C(40) carotenoids by double bond-specific cleavage enzymes (carotenoid cleavage dioxygenases, CCDs) gives rise to various apocarotenoids. AtCCD1 generating C(13) and C(14) apocarotenoids and orthologous enzymes in other plants are the only CCDs acting in the cytosol, while the hitherto presumed C(40) substrate is localized in the plastid. A new model for CCD1 action arising from a RNAi-mediated CCD1 gene silencing study in mycorrhizal hairy roots of Medicago truncatula may solve this contradiction. This approach unexpectedly resulted in the accumulation of C(27) apocarotenoids but not C(40) carotenoids suggesting C(27) as the main substrates for CCD1 in planta. It further implies a consecutive two-step cleavage process, in which another CCD performs the primary cleavage of C(40) to C(27) in the plastid followed by C(27) export and further cleavage by CCD1 in the cytosol. We compare the specificities and subcellular locations of the various CCDs and propose the plastidial CCD7 to be the first player in mycorrhizal apocarotenoid biogenesis.