not only provide sink structures that limit carotenoid turnover, but
also facilitate carotenoid biosynthesis [45].
A number of proteins have been shown to be associated with
chromoplast development or be involved in carotenoid sequestration. A small molecular chaperone HSP21 protein and a plastid
encoded fatty acid biosynthetic enzyme accD function in chromoplast development during tomato fruit ripening [128, 129]. Fibrillin
proteins participate in the formation of carotenoid-lipoprotein
complexes for carotenoid sequestration, which include CHRB
[130], PAP [131] in pepper and CHRC from cucumber [132]. A
plastid fusion and/or translocation factor (Pftf) is involved in chromoplast membrane biogenesis in pepper fruit [133]. Clearly, much
are needed to be learned for the proteins and factors that mediate
the formation of chromoplasts with great carotenoid storage
capacity.
5 Concluding Remarks
Carotenoid accumulation is a dynamic process and a net result of
biosynthesis activity, degradation rate, and stable storage in plastids.
Great progresses have been achieved in our understanding of carotenoid metabolic pathways. The main carotenoid biosynthesis pathway in plants along in bacteria, fungi, and algae is well established.
Although the enzymatic oxidative degradation by CCDs has been
determined and new CCDs for apocarotenoid production are continuously being identified, the nonspecific oxidative cleavage of
carotenoids remains to be fully elucidated. Also the identities of
some apocarotenoids and transportations are unknown. Chromoplasts are the specific plastids for massive carotenoid biosynthesis
and storage in plants. In comparison with the carotenoid biosynthesis and degradation pathways, much is unknown for the proteins
in chromoplast biogenesis pathway and sequestration processes for
carotenoid accumulation. Clearly, the advance of our knowledge
about carotenoid metabolism and storage would continuously contribute to crop nutritional quality improvement for better human
nutrition and health.
Acknowledgments
This work was supported by Agriculture and Food Research Initiative competitive award (grant no. 2016-67013-24612) from the
USDA National Institute of Food and Agriculture and by the
United States-Israel Binational Agricultural Research and Development Fund (grant no. US-4918-16CR).
16
Tianhu Sun et al.
also facilitate carotenoid biosynthesis [45].
A number of proteins have been shown to be associated with
chromoplast development or be involved in carotenoid sequestration. A small molecular chaperone HSP21 protein and a plastid
encoded fatty acid biosynthetic enzyme accD function in chromoplast development during tomato fruit ripening [128, 129]. Fibrillin
proteins participate in the formation of carotenoid-lipoprotein
complexes for carotenoid sequestration, which include CHRB
[130], PAP [131] in pepper and CHRC from cucumber [132]. A
plastid fusion and/or translocation factor (Pftf) is involved in chromoplast membrane biogenesis in pepper fruit [133]. Clearly, much
are needed to be learned for the proteins and factors that mediate
the formation of chromoplasts with great carotenoid storage
capacity.
5 Concluding Remarks
Carotenoid accumulation is a dynamic process and a net result of
biosynthesis activity, degradation rate, and stable storage in plastids.
Great progresses have been achieved in our understanding of carotenoid metabolic pathways. The main carotenoid biosynthesis pathway in plants along in bacteria, fungi, and algae is well established.
Although the enzymatic oxidative degradation by CCDs has been
determined and new CCDs for apocarotenoid production are continuously being identified, the nonspecific oxidative cleavage of
carotenoids remains to be fully elucidated. Also the identities of
some apocarotenoids and transportations are unknown. Chromoplasts are the specific plastids for massive carotenoid biosynthesis
and storage in plants. In comparison with the carotenoid biosynthesis and degradation pathways, much is unknown for the proteins
in chromoplast biogenesis pathway and sequestration processes for
carotenoid accumulation. Clearly, the advance of our knowledge
about carotenoid metabolism and storage would continuously contribute to crop nutritional quality improvement for better human
nutrition and health.
Acknowledgments
This work was supported by Agriculture and Food Research Initiative competitive award (grant no. 2016-67013-24612) from the
USDA National Institute of Food and Agriculture and by the
United States-Israel Binational Agricultural Research and Development Fund (grant no. US-4918-16CR).
16
Tianhu Sun et al.