Identification and characterization of carotenoid biosynthesis related genes in a novel dark skinned citrus mutant cultivar ‘Suneat’

We explored the relationship between skin color and the expression of genes related to carotenoid biosynthesis during fruit ripening in two citrus cultivars, ‘Shiranuhi’ (a hybrid mandarin cultivar) and ‘Suneat’ (mutant cultivar derived from a natural bud mutation of ‘Shiranuhi’). We identified 16 and 7 genes putatively involved in carotenoid biosynthesis and regulation via phylogenetic analysis in sweet orange. Further, we determined the expression pattern of these genes by quantitative real time reverse transcriptase PCR (qRT-PCR). The result showed that the expression levels of CsPSY (Cs6g15910), CsZDS (Cs3g11180), CsZ-ISO (Cs5g24730), CsBCH1 (Cs9g19270), CsFUL2 (Cs5g12280), CsTAGL1 (Cs7g16960), CsRIN1 (Cs6g19680), CsRIN2 (Cs7g10980), and CsHY5 (Cs7g05140) were up-regulated in the skin of mutant cultivar ‘Suneat’ than any other tissues of both citrus cultivars. Of these CsPSY , CsZDS , CsZ-ISO and CsBCH1 genes were related to carotenoid biosynthesis and CsFUL2 , CsTAGL1 , CsRIN1 , CsRIN2 , and CsHY5 were known to involve in the regulation of carotenoid biosynthesis. Our results reveal that the attractive dark orange skin color of ‘Suneat’ might be due to the up-regulation of carotenoid biosynthetic as well as regulatory genes and thereby higher levels carotenoids at ripening.