Genome-wide Comparative Analysis Of Carotenogenesis Genes Between Cucumis Sativus And Citrullus Lanatus

In higher plants and algae, carotenoids as components of light-harvesting-antenna complexes are synthesized in large quantities for photosynthesis, and in some bacteria and fungi which are also present. Carotenoids are also typical antioxidants, they can protect cells from oxidizing agent and prevent humans from chronic diseases. In watermelon (Citrullus lanatus L.), which belongs to Cucurbitaceae plants, lycopene is the mainly carotenoids and its content in red flesh watermelon is equal to tomato. In another Cucurbitaceae plants:cucumber (Cucumis sativus L.), there is usually none of carotenoids in fruits. The completion of the genome sequences from cucumber and watermelon, provides an opportunity for genome-wide analysis of the mechanisms of different lycopene content between the two Cucurbitaceae species at genomic level.The methods for bioinformatic analysis were used to analyze the carotenogenesis genes from the three species in the study. Firstly, a total of20carotenogenesis genes from the two species (cucumber and watermelon) were identified by BLASTP using the Genbank accession of carotenoid biosynthesis genes from tomato as queries. Phylogenetic analysis showed that carotenogenesis genes of seven plant species are closely, especically in cucumber and watermelon. And gene structures and conserved motifs composition of carotenogenesis genes from the seven species show significant similarities, except phytoene desaturase (PDS). There is a Val/Thr different between CIPDS (from watermelon), SIPDS (from tomato) and other five plant species. Genetic transformation of cucumber was used to verify the hypothesis but without genetic stability of transgenic plants now. Promoter analysis showed that ζ-carotene desaturase (ZDS), lycopene β-cyclase (LCYB) and lycopene s-cyclase (LCYE)-are highly conserved among cucumber, melon and watermelon. But the promoters of phytoene synthase (PSY1), PDS and carotene isomerase (CRTISO) in watermelon are significantly different from cucumber and melon, respectively. Using Nicotiana benthamiana transient assay system, the GUS expression of proCWSY1-546(CIPSY1promoter) was much lower than proC1PSY1-481, it indicated that one or more positive elements at the length of65bp. Otherwise, we found that the activity of CIPDS promoter was stronger than CsPDS (from cucumber), and equel to CaMV35S. Using a series of CIPDS promoter deletion constructs, we found that the key element of CIPDS promoter is between positions-295and-198from start codon ATG The promoter activity of CICRTISO (from watermelon) was little weaker than CsCRTISO (from cucumber).In summary, we performed comprehensive bioinformatics and promoter activity analyses of the carotenogenesis genes, which provided clues to uncover their biological roles in cucumber growth and development.