Carotenoids and apocarotenoids act as phytohormones and volatile precursors that influence plant development and confer aesthetic and nutritional value critical to consumer preference. Citrus fruits display considerable natural variation in carotenoid and apocarotenoid pigments. In this study, using an integrated genetic approach we revealed that a 5′ cis-regulatory change at CCD4b encoding CAROTENOID CLEAVAGE DIOXYGENASE 4b is a major genetic determinant of natural variation in C₃₀ apocarotenoids responsible for red coloration of citrus peel. Functional analyses demonstrated that in addition the known role in synthesizing β-citraurin, CCD4b is also responsible for the production of another important C₃₀ apocarotenoid pigment, β-citraurinene. Furthermore, analyses of the CCD4b promoter and transcripts from various citrus germplasm accessions established a tight correlation between the presence of a putative 5′ cis-regulatory enhancer within an MITE transposon and the enhanced allelic expression of CCD4b in C₃₀ apocarotenoid-rich red-peeled accessions. Phylogenetic analysis provided further evidence that functional diversification of CCD4b and naturally occurring variation of the CCD4b promoter resulted in the stepwise evolution of red peels in mandarins and their hybrids. Taken together, our findings provide new insights into the genetic and evolutionary basis of apocarotenoid diversity in plants, and would facilitate breeding efforts that aim to improve the nutritional and aesthetic value of citrus and perhaps other fruit crops.

类胡萝卜素和类胡萝卜素充当植物激素和挥发性前体，影响植物发育并赋予对消费者喜好至关重要的美学和营养价值。柑橘类水果在类胡萝卜素和类胡萝卜素色素中表现出相当大的自然变化。在这项研究中，我们使用综合遗传方法揭示了在CCD4b上编码类胡萝卜素裂解二氧合酶4b的5'顺式调节变化是导致柑桔皮呈红色的C ₃₀类胡萝卜素自然变化的主要遗传决定因素。功能分析表明，除了在合成β-citraurin已知的角色，CCD4b还负责生产的另一个重要Ç ₃₀类胡萝卜素色素，β-柠檬醛。此外，对来自各种柑橘种质种质的CCD4b启动子和转录本的分析建立了MITE转座子中推定的5'顺式调控增强子的存在与富含C _30的类胡萝卜素红皮中CCD4b的等位基因表达的增强之间的紧密相关性。加入。系统发育分析提供进一步的证据表明CCD4b的功能多样化的和天然存在的变异CCD4b启动子导致橘子及其杂种中红皮的逐步进化。综上所述，我们的发现为植物中类胡萝卜素多样性的遗传和进化基础提供了新的见识，并将促进旨在提高柑橘以及其他水果作物的营养和美学价值的育种工作。