Table_1_Fine mapping and identifying candidate gene of Y underlying yellow peel in Cucurbita pepo.xlsx

As a conspicuous trait, peel color is one of the most important characteristics that affects commodity quality and consumer preferences. The locus Y underlying yellow peel in Cucurbita pepo (zucchini) was first reported in 1922; however, its molecular mechanism is still unknown. In this study, a genetic analysis revealed that yellow peel is controlled by a single dominant genetic factor. Furthermore, Y was mapped in a ~170 kb region on chromosome 10 by bulked segregated analysis (BSA) and fine mapping in F2 and BC1 segregating populations. The candidate region harbors fifteen annotated genes, among which Cp4.1LG10g11560 (CpCHLH) is regarded as a promising candidate gene. CpCHLH encodes a magnesium chelatase H subunit involved in chlorophyll biosynthesis, and its mutation can result in a reduction in chlorophyll content and yellow phenotype. Interestingly, a large fragment (~15 kb) duplication containing incomplete CpCHLH was inserted in the candidate interval, resulting in two reformed CpCHLH proteins in the yellow parental line. It is most likely that the reformed CpCHLH proteins act as a malfunctional competitor of the normal CpCHLH protein to interrupt the formation of chlorophyll. Overall, the isolation of Y will shed light on the molecular mechanism of the peel color regulation of zucchini and lay a foundation for breeding.

果皮颜色作为一项显著性状，是影响商品品质与消费者偏好的核心特征之一。西葫芦（Cucurbita pepo）中调控黄色果皮的Y基因座最早于1922年被报道，但其分子机制至今仍未明确。本研究通过遗传分析证实，黄色果皮由单个显性遗传因子调控。此外，本研究通过集群分离分析法（bulked segregated analysis, BSA）以及F₂和回交一代（BC₁）分离群体的精细定位，将Y基因座定位至10号染色体上约170 kb的区间内。该候选区间内包含15个已注释基因，其中Cp4.1LG10g11560（CpCHLH）被视为最具潜力的候选基因。CpCHLH编码参与叶绿素生物合成的镁螯合酶H亚基，其突变可导致叶绿素含量降低并呈现黄色表型。值得注意的是，该候选区间内插入了一段包含不完整CpCHLH序列的约15 kb大片段重复序列，使得黄色果皮亲本中产生了两种重构的CpCHLH蛋白。极有可能，这些重构的CpCHLH蛋白作为正常CpCHLH蛋白的功能异常竞争性抑制剂，阻断了叶绿素的合成过程。综上，Y基因座的克隆将为解析西葫芦果皮颜色调控的分子机制提供重要线索，并为西葫芦育种工作奠定基础。