from Bixa orellana seed coats, is an important commercial pigment.
Lycopene cleave dioxygenase (LCD) along with bixin aldehyde
dehydrogenase and norbixin carboxyltransferase convert lycopene
into bixin [94].
Apart from ABA and strigolactones, emerging evidences have
revealed that a class of apocarotenoids function as signal molecules
(Fig. 2) to regulate plant growth and development [95]. Apocarotenoids β-cyclocitral and β-ionone derived from nonenzymatic
cleavage of β-carotene act as photo-oxidative stress signals to mediate stress-related gene expression under high light
[96, 97]. Recently, a novel apocarotenoid metabolite zaxinone
was identified as a regulator of plant development and mycorrhization [98]. There are also some uncharacterized apocarotenoid signals involved in the regulation of different biological processes in
plants. Examples include a signal found in a ζ-carotene desaturase
mutant in regulating chloroplast and leaf development [99], a
signal in mediating lateral root branching [100], and apocarotenoids derived from prolycopene or cis-neurosporene in controlling
the transcription of PSY1 to affect tomato fruit color [101]. In
addition, two types of apocarotenoids, glycosylated C13 α-ionols
derivatives previously called cyclohexenone derivatives and C14
yellow pigment mycorradicin, cleaved by CCD7 and CCD1, are
participated in arbuscular mycorrhizal symbiosis like strigolactones
[102–104].
3.5 Apocarotenoid
Transportation
Carotenoids are mainly localized in plastids in plants. Notably some
carotenoids, especially apocarotenoids and ketocarotenoids, are
found and metabolized outside of plastids. In Crocus sativus flower
stigma and Bixa seed arils, apocarotenoids like crocins or bixin are
formed in plastids, but store in vacuole in significant amounts
[105, 106]. Xanthoxin, the cleavage product of the 9-cis-xanthophylls, is produced in plastids and converted to ABA in cytosol
[64]. Carlactone is another carotenoid cleavage product that is
cleaved in plastids and catalyzed into strigolactone in cytosol
[107, 108]. Similarly, the carotenoids or apocarotenoids cleaved
by CCD1 likely are present outside of plastids as CCD1 is localized
in cytosol. Moreover, several green algae accumulate ketocarotenoids, especially astaxanthin, in cytoplasmic vesicles [109]. These
observations imply that some apocarotenoids or ketocarotenoids
are transported or trafficked from their sites of synthesis in plastids
to other subcellular locations by unknown mechanisms. Crocins
in Crocus sativus are thought to be transported via ABC
transporter family [110] and via endoplasmic reticulum and cytoplasm [111]. However, the transport processes remain poorly
understood.
Pathways for Carotenoid Biosynthesis, Degradation, and Storage
13
Lycopene cleave dioxygenase (LCD) along with bixin aldehyde
dehydrogenase and norbixin carboxyltransferase convert lycopene
into bixin [94].
Apart from ABA and strigolactones, emerging evidences have
revealed that a class of apocarotenoids function as signal molecules
(Fig. 2) to regulate plant growth and development [95]. Apocarotenoids β-cyclocitral and β-ionone derived from nonenzymatic
cleavage of β-carotene act as photo-oxidative stress signals to mediate stress-related gene expression under high light
[96, 97]. Recently, a novel apocarotenoid metabolite zaxinone
was identified as a regulator of plant development and mycorrhization [98]. There are also some uncharacterized apocarotenoid signals involved in the regulation of different biological processes in
plants. Examples include a signal found in a ζ-carotene desaturase
mutant in regulating chloroplast and leaf development [99], a
signal in mediating lateral root branching [100], and apocarotenoids derived from prolycopene or cis-neurosporene in controlling
the transcription of PSY1 to affect tomato fruit color [101]. In
addition, two types of apocarotenoids, glycosylated C13 α-ionols
derivatives previously called cyclohexenone derivatives and C14
yellow pigment mycorradicin, cleaved by CCD7 and CCD1, are
participated in arbuscular mycorrhizal symbiosis like strigolactones
[102–104].
3.5 Apocarotenoid
Transportation
Carotenoids are mainly localized in plastids in plants. Notably some
carotenoids, especially apocarotenoids and ketocarotenoids, are
found and metabolized outside of plastids. In Crocus sativus flower
stigma and Bixa seed arils, apocarotenoids like crocins or bixin are
formed in plastids, but store in vacuole in significant amounts
[105, 106]. Xanthoxin, the cleavage product of the 9-cis-xanthophylls, is produced in plastids and converted to ABA in cytosol
[64]. Carlactone is another carotenoid cleavage product that is
cleaved in plastids and catalyzed into strigolactone in cytosol
[107, 108]. Similarly, the carotenoids or apocarotenoids cleaved
by CCD1 likely are present outside of plastids as CCD1 is localized
in cytosol. Moreover, several green algae accumulate ketocarotenoids, especially astaxanthin, in cytoplasmic vesicles [109]. These
observations imply that some apocarotenoids or ketocarotenoids
are transported or trafficked from their sites of synthesis in plastids
to other subcellular locations by unknown mechanisms. Crocins
in Crocus sativus are thought to be transported via ABC
transporter family [110] and via endoplasmic reticulum and cytoplasm [111]. However, the transport processes remain poorly
understood.
Pathways for Carotenoid Biosynthesis, Degradation, and Storage
13