Novel Carotenoid Pathway-related Gene Expression Patterns in Citrus Leaves and Maturing Fruits

Carotenoids are abundant in citrus fruits and vary among cultivars and species. In the present study, HPLC and real-time PCR were used to investigate the expression patterns of 23 carotenoid biosynthesis gene family members and their possible relation with carotenoid accumulation in flavedo, juice sacs, and leaves of Valencia orange during fruit maturation. Violaxanthin and lutein mainly accumulated in fruit (flavedo and juice sacs) and leaves (young and mature), respectively, accounting for nearly 79%, 57%, 53% and 70% of corresponding total carotenoids in February. Violaxanthin content quickly began to increase in flavedo in December, but the increase in juice sacs began later in January. In mature leaves, lutein content was 3 times that in young leaves; α-carotene and β-carotene were also much higher in mature leaves than in flavedo or juice sacs. Most of the carotenoid biosynthesis gene members were expressed at higher levels in flavedo than in juice sacs, and the expressions of PSY-Contig22, ZDS-Contig23, CHYB-Contig25, and CHYB-Contig07 continued to increase in flavedo during fruit maturation. PSY-Contig10 and LCYE-Contig24 were not detected in juice sacs, and the expression of the other gene family members in juice sacs fluctuated. All CHYB members expressed at high levels and had similar patterns in juice sacs. The CCS members had similar expression levels and patterns in flavedo and juice sacs. In leaf, the expression levels of LCYB-Contig21 was much higher than in flavedo or juice sacs, but the CHYB members and CCS-Contig16 were expressed at low levels, and PSY-Contig10 and CCS-Contig19 were not detected. The expression of ZDS-Contig08 was not detected in any of the three tissues. Pearson correlation analysis showed that the expression of some gene family members had more significant correlations with each other in juice sacs than in flavedo or leaves. Moreover, the expression of CHYB gene family members had significantly negative correlations with carotenoid accumulation in leaves. The expression patterns of these 23 citrus carotenoid biosynthesis gene members were also compared with their expression patterns in other plants. Taken together, these first-hand expression data will be useful to define the tissue-specific roles of each gene member in accumulation of different carotenoids in citrus leaves and maturing fruits.