Abstract
In plants, the
carotenoid cleavage dioxygenase 4
(
CCD4
) could target on plastoglobules and cleave specific carotenoids, producing apocarotenoids and volatile compounds. These compounds are important for color and aroma formation in fruits and flowers. In this study, five
CCD4
gene members (
CCD4a, b, c, d,
and
e
) were investigated in different citrus species including mandarin, pummelo, and sweet orange. Sequence analysis showed that the
CCD4
genes from all the species examined exhibited extensive allelic variability (including SNPs and frame-shift mutations). Furthermore, the distribution of the
CCD4
allelic mutation sites supported our previous hypothesis that the sweet orange originated from the hybridization of mandarin and pummelo. A derived cleaved amplified polymorphic sequence (dCAPs) marker was then successfully developed based on the allelic polymorphism of
CCD4c
, providing an ideal molecular marker for studying the genetic relationship between citrus species. Quantitative RT-PCR analysis identified differential expression patterns for the
CCD4
genes in tissues/organs, and
CCD4b
was shown to have a high-level expression in citrus fruit flavedos (especially those with a deep orange-reddish color). HPLC-based detection of a key component (i.e., β-citraurin) for orange-reddish flavedo formation in different citrus revealed a positive correlation between
CCD4b
expression levels and the presence of β-citraurin, suggesting that
CCD4b
may be responsible for β-citraurin biosynthesis in flavedo. In summary, this study not only reinforced the anticipated roles of
CCD4
genes in flavedo color formation in citrus, but also provided new information about gene expression patterns, allelic polymorphism characteristics, and sequence variability for this gene subfamily.