Gonzalez-Jorge Sabrina, Ha Sun-Hwa, Magallanes-Lundback Maria, Gilliland Laura Ullrich, Zhou Ailing, Lipka Alexander E, Nguyen Yen-Nhu, Angelovici Ruthie, Lin Haining, Cepela Jason, Little Holly, Buell C Robin, Gore Michael A, Dellapenna Dean
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319.
Plant Cell. 2013 Dec;25(12):4812-26. doi: 10.1105/tpc.113.119677. Epub 2013 Dec 24.
Experimental approaches targeting carotenoid biosynthetic enzymes have successfully increased the seed β-carotene content of crops. However, linkage analysis of seed carotenoids in Arabidopsis thaliana recombinant inbred populations showed that only 21% of quantitative trait loci, including those for β-carotene, encode carotenoid biosynthetic enzymes in their intervals. Thus, numerous loci remain uncharacterized and underutilized in biofortification approaches. Linkage mapping and genome-wide association studies of Arabidopsis seed carotenoids identified CAROTENOID cleavage dioxygenase4 (CCD4) as a major negative regulator of seed carotenoid content, especially β-carotene. Loss of CCD4 function did not affect carotenoid homeostasis during seed development but greatly reduced carotenoid degradation during seed desiccation, increasing β-carotene content 8.4-fold relative to the wild type. Allelic complementation of a ccd4 null mutant demonstrated that single-nucleotide polymorphisms and insertions and deletions at the locus affect dry seed carotenoid content, due at least partly to differences in CCD4 expression. CCD4 also plays a major role in carotenoid turnover during dark-induced leaf senescence, with β-carotene accumulation again most strongly affected in the ccd4 mutant. These results demonstrate that CCD4 plays a major role in β-carotene degradation in drying seeds and senescing leaves and suggest that CCD4 orthologs would be promising targets for stabilizing and increasing the level of provitamin A carotenoids in seeds of major food crops.
针对类胡萝卜素生物合成酶的实验方法已成功提高了作物种子中的β-胡萝卜素含量。然而，对拟南芥重组自交群体种子类胡萝卜素的连锁分析表明，包括β-胡萝卜素相关位点在内，只有21%的数量性状位点在其区间内编码类胡萝卜素生物合成酶。因此，在生物强化方法中，许多位点仍未得到表征和利用。拟南芥种子类胡萝卜素的连锁图谱绘制和全基因组关联研究确定了类胡萝卜素裂解双加氧酶4（CCD4）是种子类胡萝卜素含量，尤其是β-胡萝卜素的主要负调控因子。CCD4功能的丧失在种子发育过程中不影响类胡萝卜素稳态，但在种子干燥过程中极大地减少了类胡萝卜素降解，相对于野生型，β-胡萝卜素含量增加了8.4倍。ccd4缺失突变体的等位基因互补表明，该位点的单核苷酸多态性以及插入和缺失影响干种子类胡萝卜素含量，至少部分原因是CCD4表达的差异。CCD4在黑暗诱导的叶片衰老过程中的类胡萝卜素周转中也起主要作用，β-胡萝卜素积累在ccd4突变体中再次受到最强烈的影响。这些结果表明，CCD4在干燥种子和衰老叶片的β-胡萝卜素降解中起主要作用，并表明CCD4直系同源物将是稳定和提高主要粮食作物种子中维生素A原类胡萝卜素水平的有前景的靶点。
