RESEARCH PAPER |
A novel bud mutation that confers abnormal patterns of lycopene accumulation in sweet orange fruit (Citrus sinensis L. Osbeck)
1National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, PR China
2Guangxi Citrus Research Institute, Guangxi 541004, PR China
* To whom correspondence should be addressed. E-mail: xxdeng{at}mail.hzau.edu.cn
A novel, pleiotropic sweet orange (Citrus sinensis L. Osbeck) mutant, ‘Hong Anliu’, is described. This mutation causes carotenoid accumulation, high sugar, and low acid in the fruits. Gas chromatographic analysis revealed that high sugar and low acid in the fruit were caused by the accumulation of sucrose and the deficiency of citric acid. The dominant carotenoid accumulated in albedo, segment membranes, and juice sacs is lycopene, which can reach levels that are a 1000-fold higher than those in comparable wild-type fruits. This mutation does not affect the carotenoid composition of leaves. Carotenoid concentration and biosynthetic gene expression of albedo, segment membranes, and juice sacs were dramatically altered by the mutation. Lycopene accumulation in the juice sacs was regulated by co-ordinate expression of carotenoid biosynthetic genes. However, in albedo and segment membranes, the expression of downstream carotenogenic genes seems to be feedback induced by lycopene accumulation. This implies that there must be at least two modes regulating lycopene accumulation in ‘Hong Anliu’ fruit. Taken together, these results suggest that massive amounts of lycopene might be synthesized in the juice sacs and then transported to the segment membrane and the albedo, which leads to lycopene accumulation there.
Key words: Bud mutation, carotenoid biosynthesis, Citrus, gene expression, lycopene, transport
Received 15 August 2007; Revised 2 October 2007 Accepted 8 October 2007