Novel expression patterns of carotenoid pathway-related gene in citrus leaves and maturing fruits

Authors: WEI, XU - Southwest University; Chen, Chunxian; YU, QIBIN - University Of Florida; GADY, ANTOINE - University Of Florida; YU, YUAN - University Of Florida; LIANG, GUOLU - Southwest University; GMITTER, FRED - University Of Florida

Submitted to: Tree Genetics and Genomes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2013
Publication Date: 1/24/2014
Publication URL: http://link.springer.com/journal/11295
Citation: Wei, X., Chen, C., Yu, Q., Gady, A., Yu, Y., Liang, G., Gmitter, F.J. 2014. Novel expression patterns of carotenoid pathway-related gene in citrus leaves and maturing fruits. Tree Genetics and Genomes. 10(3):439-448.

Interpretive Summary: Diverse fruit colors are an important attribute for marketing appeal and healthy nutrition. One of the main coloration (pigmentation) sources is carotenoids, a group of pigments found in citrus, peach, carrot, pepper, and many other fruits and vegetables. Carotenoids vary among cultivars and species in compositions and levels, but little knowledge has been gained to understand the relation between the carotenoid color variability and the controlling and regulatory genes in their biosynthesis pathway. Quantification of the various pigments and biosynthetic gene expressions in maturing citrus fruits will be helpful to reveal the possible relation.

Technical Abstract: 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; a-carotene and ß-carotene were also much higher in mature leaves than in flavedo or juice sacs. Generally most of the carotenoid biosynthesis gene members were expressed at higher levels in flavedo than in juice sacs, and the expression of PSY-Contig22, ZDS-Contig23, CHYB-Contig25 and CHYB-Contig07 in particular 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. Interestingly, 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. Additionally, 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.