Largely different carotenogenesis in two pummelo fruits with different flesh colors

Abstract

Carotenoids in citrus fruits have health benefits and make the fruits visually attractive. Red-fleshed ‘Chuhong’ (‘CH’) and pale green-fleshed ‘Feicui’ (‘FC’) pummelo (Citrus maxima (Burm) Merr.) fruits are interesting materials for studying the mechanisms of carotenoid accumulation. In this study, particularly high contents of linear carotenes were observed in the albedo tissue, segment membranes and juice sacs of ‘CH’. However, carotenoids, especially β-carotene and xanthophylls, accumulated more in the flavedo tissue of ‘FC’ than in that of ‘CH’. Additionally, the contents of other terpenoids such as limonin, nomilin and abscisic acid significantly differed in the juice sacs at 150 days postanthesis. A dramatic increase in carotenoid production was observed at 45 to 75 days postanthesis in the segment membranes and juice sacs of ‘CH’. Different expression levels of carotenogenesis genes, especially the ζ-carotene desaturase (CmZDS), β-carotenoid hydroxylase (CmBCH) and zeaxanthin epoxidase (CmZEP) genes, in combination are directly responsible for the largely different carotenoid profiles between these two pummelo fruits. The sequences of eleven genes involved in carotenoid synthesis were investigated; different alleles of seven of eleven genes might also explain the largely different carotenogenesis observed between ‘CH’ and ‘FC’. These results enhance our understanding of carotenogenesis in pummelo fruits.

The IAA- and ABA-responsive transcription factor CgMYB58 upregulates lignin biosynthesis and triggers juice sac granulation in pummelo

“…ABA is one of the downstream metabolites of carotenoids. Our previous reports showed that the ABA concentration was higher in pale-fleshed Feicui pummelo fruits than in red-fleshed Chuhong pummelo fruits at 150 DPA 25 . In addition, ABA has been reported to be involved in the regulation of lignin biosynthetic genes and TF regulators that respond to the lignin accumulation process in plants 34 .…”

“…Citrus fruits, which are the most popular fruits worldwide, provide an assortment of functional components that are beneficial to human health, including flavonoids 19,20 , volatile compounds 21 , alkaloids 22 , and carotenoids [23][24][25][26] . However, in citrus fruit juice sacs, overaccumulation of lignin (a physiological disorder known as granulation) often occurs 9,10,27,28 .…”

A mutant allele of zeta-carotene isomerase (Z-ISO) is associated with the yellow pigmentation of the ‘Pinalate’ sweet orange mutant and reveals new insights into its role in fruit carotenogenesis

“…1). The expression of CRTISO in different Citrus species does not correlate with the b,b-xanthophylls accumulation [12], and the characterization of citrus Z-ISO is restricted to pummelo (Citrus maxima) [29].…”

A mutant allele of zeta-carotene isomerase (Z-ISO) is associated with the yellow pigmentation of the ‘Pinalate’ sweet orange mutant and reveals new insights into its role in fruit carotenogenesis

“…1). The expression of CRTISO during ripening has been analyzed in different Citrus species and does not correlate with accumulation of b,b-xanthophylls [12], and the characterization of citrus Z-ISO is very limited and restricted to pummelo (Citrus maxima), an ancient citrus species [29].…”

“…The Rohde Red Valencia is another sweet orange mutant with altered pigmentation, which shows an intense orange pulp associated to higher accumulation of β-cryptoxanthin and expression of PDS, ZDS and ZEP genes compared to parental cultivar [39]. Most of the sweet orange mutants with altered pigmentation display an intense pulp or peel coloration compared to ordinary cultivars due to attractiveness for breeders and consumers; however, research on varieties with defective fruit pigmentation is scarce and limited to other citrus species such as mandarins, pummelo or grapefruit [19,29,40,41,42,43,44]. A significant exception among sweet oranges is the mutant Pinalate, a spontaneous bud mutant from Navelate genotype.…”