Color is a crucial component of the commercial value of citrus fruits. Carotenoid cleavage oxygenases (CCOs) can affect fruit color by oxidative cleavage of different carotenoid sites, resulting in various colors. This study proposed a genome-wide analysis of the Orah mandarin CCO gene family using bioinformatics methods and combined physiological, transcriptomic, and metabolomic data to analyze the gene expression levels and carotenoid accumulation mechanisms of different colored peel. A total of 14 CCOs were identified in the Orah mandarin genome. Phylogenetic analysis revealed that CrCCOs can be classified into six subfamilies, and the gene structure and conserved motifs support the above classification. GO and KEGG functional annotation revealed that Orah mandarin CCO genes play crucial roles in carotenoid synthesis and catabolism. Transcriptomic data showed that the expression level of CrCCD4b1 was positively correlated with the current status of Orah mandarin red flavedo. Physiological and metabolomic studies further revealed that apocarotenal and β-citraurin were identified as the key metabolites controlling the change in flavedo color from yellow to red. Correlation analysis revealed CrCCD4b1 as a crucial gene in the apocarotenal and β-citraurin expression network. For the first time, we proposed CrCCD4b1 as a potential model for increasing red carotenoid accumulation in the flavedo by promoting the biosynthesis of C30 carotenoids (apocarotenal, β-citraurin) in Orah mandarin. This study will lay the foundation for further research on the causes of differences in peel color and the mining of crucial genes regulating the red trait.

中文翻译：

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奥拉柑橘类胡萝卜素裂解加氧酶基因的全基因组鉴定及CrCCD4b1影响果皮颜色的机制


颜色是柑橘类水果商业价值的重要组成部分。类胡萝卜素裂解加氧酶（CCO）可以通过不同类胡萝卜素位点的氧化裂解来影响果实颜色，从而产生各种颜色。本研究提出利用生物信息学方法对Orah柑橘CCO基因家族进行全基因组分析，并结合生理学、转录组学和代谢组学数据，分析不同颜色果皮的基因表达水平和类胡萝卜素积累机制。 Orah 柑橘基因组中总共鉴定出 14 个 CCO。系统发育分析表明，CrCCOs可分为6个亚科，基因结构和保守基序支持上述分类。 GO和KEGG功能注释揭示了Orah柑橘CCO基因在类胡萝卜素合成和分解代谢中发挥着至关重要的作用。转录组数据显示，CrCCD4b1的表达水平与Orah柑橘的现状呈正相关。生理和代谢组学研究进一步表明，阿朴胡萝卜醛和β-柠檬酸被确定为控制黄皮颜色从黄色到红色变化的关键代谢物。相关性分析表明 CrCCD4b1 是 apocar​​otenal 和 β-citraurin 表达网络中的关键基因。我们首次提出 CrCCD4b1 作为潜在模型，通过促进 Orah 柑橘中 C30 类胡萝卜素（阿朴胡萝卜醛，β-柠檬酸苷）的生物合成来增加黄皮中红色类胡萝卜素的积累。本研究将为进一步研究果皮颜色差异的原因以及挖掘调控红色性状的关键基因奠定基础。