Abstract Red-fleshed pummelo (Citrus grandis), a mutant of ‘Guanxi’, is an important economic plant rich in carotenoids. The transcriptome of ‘Guanxi’ pummelo was compared with red-fleshed pummelo, with the aim of identifying the key genes responsible for red flesh through RNA sequencing. In total, 44.11 and 47.71 Gb clean reads were respectively obtained after filtering in red and white flesh. Altogether 46,425 unigenes, with an average length of 1208 bp, were assembled. Compared with that of white flesh, 3722 genes were up-regulated, whereas 1421 genes appeared down-regulated in the red-fleshed pummelo. A GO analysis assigned 11,983 differentially expressed genes to 53 subcategories, and 3582, 4722 and 3679 differentially expressed genes were involved in biological processes, cellular components and molecular functions, respectively. The mevalonate pathway involved in terpenoid backbone biosynthesis was significantly different between ‘Guanxi’ pummelo and its red-fleshed mutant, and the differences were closely associated with carotenoid biosynthesis. The expression levels of the carotenoid biosynthetic pathway genes were different between ‘Guanxi’ pummelo and its red-fleshed mutant, with the upstream genes having higher expression levels in red-fleshed pummelo than in ‘Guanxi’ pummelo, whereas the downstream gene β-CHX was downregulated. Two bHLH transcription factors (CL4778.Contig1 and CL4778.Contig2) were of the same branch as CubHLH1, regulating carotenoid biosynthesis in Citrus unshiu Marc., and Unigene CL4778.Contig2 had expression differences in two kinds of pummelo, which suggested CL4778.Contig2 should be a candidate gene controlling carotenoid accumulation in red pummelo. The study would be beneficial to identify the major gene regulating the red flesh trait.

中文翻译：

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转录组分析确定了参与红柚（Citrus maxima）果肉中类胡萝卜素生物合成的关键基因

摘要 红肉柚（Citrus grandis）是'关西'的突变体，是一种富含类胡萝卜素的重要经济植物。将‘关西’柚子的转录组与红肉柚子进行比较，目的是通过RNA测序确定导致红肉的关键基因。在红色和白色果肉中过滤后，总共分别获得了 44.11 和 47.71 Gb 的干净读数。总共组装了 46,425 个 unigenes，平均长度为 1208 bp。与白肉相比，3722个基因上调，而红肉柚中有1421个基因下调。GO 分析将 11,983 个差异表达基因分配到 53 个亚类，3582、4722 和 3679 个差异表达基因分别参与生物过程、细胞成分和分子功能。'关西'柚及其红肉突变体参与萜类骨架生物合成的甲羟戊酸途径存在显着差异，该差异与类胡萝卜素生物合成密切相关。'关西'柚及其红肉突变体类胡萝卜素生物合成途径基因的表达水平存在差异，上游基因在红肉柚中的表达量高于'关西'柚，而下游基因β-CHX被下调。两个bHLH转录因子（CL4778.Contig1和CL4778.Contig2）与CubHLH1属于同一分支，调控Citrus unshiu Marc.类胡萝卜素的生物合成，Unigene CL4778.Contig2在两种柚子中表达差异，提示CL4778。Contig2 应该是控制红柚中类胡萝卜素积累的候选基因。该研究将有助于确定调节红肉性状的主要基因。