Abstract: arotenoid cleavage dioxygenase（CCD）can catalyze the oxidative cleavage of carotenoidsa t specific sites to generate a variety of bioactive compounds. To some extent，their activities determine the arotenoid content and composition in plants. In this study，the CCD1 gene was cloned from fruits of Cara Cara navel orange（Citrus sinensis L. Osbeck）. The RNAi construct，pHGRV-CCD1，was constructed by inserting CCD1 specific fragments into plasmid pHGRV via recombination，and then introduced into calli of Satsuma mandarin Guoqing 1，Valencia sweet orange and Marsh grapefruit by Agrobacterium-mediated transformation. As a result，6，4 and 4 transgenic lines were obtained respectively. Compared with the wild-type，expression level of the transgenic lines were significantly downregulated to various degrees，among which the CCD1 expression of Marsh grapefruit transgenic line Rm2 was only 8.4% of control as the greatest interference effect. Most transformed calli with CCD1 RNAi construct exhibited similar color phenotype to wild-type controls except for Rm2 line（macroscopic color changes）. Compared with the wild-type，the inhibition of CCD1 gene expression resulted in a significant increase of violaxanthin and 9-cis-violaxanthin content，suggesting these two compounds might be the preferred in vivo cleavage substrates of CCD1 in citrus calli.

Key words: citrus, carotenoid, carotenoid cleavage dioxygenases, RNAi technology, calli