Biochemical and Molecular Factors Governing Peel-Color Development in ‘Ora’ and ‘Shani’ Mandarins

To
identify factors governing peel-color development in mandarins,
we examined carotenoid content and composition and the expression
of carotenoid-related genes during four stages of ripening (i.e.,
green, breaker, yellow, and orange) in two varieties: ‘Ora’,
which has orange fruit, and ‘Shani’, which has orange-reddish
fruit. The two varieties had different carotenoid compositions, and
‘Shani’ had a significantly higher level of total carotenoid
pigments. ‘Shani’ was rich in the deep orange β-cryptoxanthin
and the orange-reddish β-citraurin, whereas ‘Ora’
was rich in the orange violaxanthin. RNA-Seq analysis revealed significantly
greater expression of the carotenoid-biosynthesis genes PSY, βLCY, βCHX, and CCD4b, as well as MEP-pathway genes and several ethylene-biosynthesis
and -signaling genes in ‘Shani’ fruit. In contrast,
the expression levels of genes involved in the synthesis of α-branch
carotenoids (i.e., εLCY and εCHX) and ZEP, which is involved in the formation of
violaxanthin, were significantly higher in the ‘Ora’
fruit.