Biosynthesis and Esterification of Carotenoids During Fruit Ripening
Fruits are the main sources of carotenoid esters in the human diet; thus, the biosynthesis and regulation of carotenoids during fruit development and ripening are fundamental to understanding the esterification process. During the last decade, significant efforts have been dedicated to deciphering the physiological, biochemical and molecular mechanisms responsible for the specific and highly diverse carotenoid patterns in fruits. The rapid expansion of multi-omics strategies in important agronomical species has made it possible to establish the basic metabolic sequence of carotenoid biosynthesis that modulates carotenoid changes during fruit development and ripening. The main mechanism governing carotenoid accumulation in fruit tissues is exerted by the transcriptional regulation of structural biosynthetic and catabolic genes. Several pieces of evidence indicate that xanthophyll esterification during ripening is a genetically controlled process allowing their massive accumulation in plastoglobuli, specifically subplastidial structures. However, the unequivocal identification of the enzyme(s) involved in xanthophyll esterification in fruits has not been established, and the genetic basis of ester formation is mostly unknown. This chapter focuses on the common mechanisms governing carotenoid biosynthesis and accumulation in fleshy fruits with an emphasis on fruits with significant accumulation of esterified carotenoids and their relationship with the dynamic changes in carotenoid ester profile occurring during development and ripening.