Cloning of the Papaya Chromoplast-Specific Lycopene β-Cyclase, CpCYC-b, Controlling Fruit Flesh Color Reveals Conserved Microsynteny and a Recombination Hot Spot
Cloning of the Papaya Chromoplast-Specific Lycopene β-Cyclase, CpCYC-b, Controlling Fruit Flesh Color Reveals Conserved Microsynteny and a Recombination Hot Spot
复制标题
DOI：
10.1104/pp.109.152298
复制
发表时间：
2010-04-01
期刊：
影响因子：
7.4
通讯作者：
Yu, Qingyi
中科院分区：
文献类型：
--
作者：
Blas, Andrea L.;Ming, Ray;Yu, Qingyi
水果中的类胡萝卜素色素是成熟过程和潜在营养价值的指示。番木瓜（Carica papaya）果实的果肉颜色是由色素体中番茄红素或β-类胡萝卜素的积累引起的。它是影响营养成分、水果质量、保质期和消费者偏好的显著特征。为了揭示番木瓜果肉颜色的分子基础，我们采用整合遗传图谱和物理图谱的图位克隆和候选基因的方法。与果肉颜色紧密相关的DNA标记与番茄（Solanum lycopersicum）染色体特异性番茄红素β-环化酶CYC-b的cDNA探针共定位在物理图谱的重叠群上。从扩增片段中获得候选基因序列，并通过对含有两个等位基因的两个细菌人工染色体进行测序来验证。序列比较显示，在隐性红肉等位基因的编码区中插入2个碱基，导致移码突变和提前终止密码子。细菌颜色互补试验证实了番木瓜CpCYC-b基因是控制果肉颜色的基因。野生和栽培番木瓜种质的序列分析表明，这种移码突变的存在下，在所有的红肉种质研究。CpCYC-b附近的DNA标记的评估揭示了重组热点，显示CpCYC-b位于基因丰富的区域，重组率为3.7 kb/cm 2，比基因组平均值400 kb/cm 2高100倍以上。CpCYC-b区域的保守微共线性由番木瓜、拟南芥（Arabidopsis thaliana）、葡萄（葡萄属vinifera）和番茄之间的2至4个基因的共线性指示。我们的研究结果增强了我们对番木瓜果肉颜色遗传的理解，并为番木瓜的改良提供了新的工具。
Carotenoid pigments in fruits are indicative of the ripening process and potential nutritional value. Papaya (Carica papaya) fruit flesh color is caused by the accumulation of lycopene or beta-carotenoids in chromoplasts. It is a distinct feature affecting nutritional composition, fruit quality, shelf life, and consumer preference. To uncover the molecular basis of papaya flesh color, we took map-based cloning and candidate gene approaches using integrated genetic and physical maps. A DNA marker tightly linked to flesh color colocalized on a contig of the physical map with a cDNA probe of the tomato (Solanum lycopersicum) chromoplast-specific lycopene beta-cyclase, CYC-b. Candidate gene sequences were obtained from amplified fragments and verified by sequencing two bacterial artificial chromosomes containing the two alleles. Sequence comparison revealed a 2-bp insertion in the coding region of the recessive red flesh allele resulting in a frame-shift mutation and a premature stop codon. A color complementation test in bacteria confirmed that the papaya CpCYC-b is the gene controlling fruit flesh color. Sequence analysis of wild and cultivated papaya accessions showed the presence of this frame-shift mutation in all red flesh accessions examined. Evaluation of DNA markers near CpCYC-b revealed a recombination hot spot, showing that CpCYC-b is located in a gene-rich region with a recombination rate at 3.7 kb per centimorgan, more than 100-fold higher than the genome average at 400 kb per centimorgan. Conserved microsynteny of the CpCYC-b region is indicated by colinearity of two to four genes between papaya, Arabidopsis (Arabidopsis thaliana), grape (Vitis vinifera), and tomato. Our results enhanced our understanding of papaya flesh color inheritance and generated new tools for papaya improvement.