A Cucurbita pepo EMS mutant with multiple defects in growth and development has been identified and characterized. The mutant dwfcp displayed a dwarf phenotype with dark green and shrinking leaves, shortened internodes and petioles, shorter but thicker roots and greater root biomass, and reduced fertility. The causal mutation of the phenotype was found to disrupt gene Cp4.1LG17g04540, the squash orthologue of the Arabidopsis brassinosteroids biosynthesis gene DWF5, encoding for 7-dehydrocholesterol reductase. A single nucleotide transition (G>A) causes a splicing defect in intron six that leads to a premature stop codon and a truncated CpDWF5 protein. The mutation co-segregated with the dwarf phenotype in a large BC1S1 segregating population. Reduced expression of CpDWF5 and brassinolide content in most mutant organs, and partial rescue of the mutant phenotype by exogenous application of brassinolide, showed that the primary cause of the dwarfism in dwfcp is a brassinosteroids deficiency. The results showed that in Cucurbita pepo, CpDWF5 is not only a positive growth regulator of different plant organs, but also a negative regulator of salt tolerance. During germination and early stages of seedling development, the dwarf mutant was less affected by salt stress than the wild-type, concomitantly with a greater up-regulation of genes associated with salt tolerance, including those involved in ABA biosynthesis, ABA and Ca2+ signaling, and those coding for cation exchangers and transporters.

中文翻译：

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油菜素类固醇生物合成基因 CpDWF5 的突变会破坏南瓜 (Cucurbita pepo) 的营养和生殖发育以及盐胁迫反应

一种在生长和发育方面存在多种缺陷的 Cucurbita pepo EMS 突变体已被鉴定和表征。突变体dwfcp表现出矮化表型，叶片深绿色且皱缩，节间和叶柄缩短，根较短但较粗，根生物量较大，且肥力降低。该表型的因果突变被发现破坏了基因 Cp4.1LG17g04540，该基因是拟南芥油菜素类固醇生物合成基因 DWF5 的南瓜直系同源物，编码 7-脱氢胆固醇还原酶。单核苷酸转变(G>A)导致内含子六中的剪接缺陷，导致过早终止密码子和截短的CpDWF5蛋白。该突变与大型 BC1S1 分离群体中的矮化表型共分离。大多数突变器官中 CpDWF5 表达和油菜素内酯含量降低，以及通过外源应用油菜素内酯部分挽救突变表型，表明 dwfcp 侏儒症的主要原因是油菜素类固醇缺乏。结果表明，在Cucurbita pepo中，CpDWF5不仅是不同植物器官生长的正调节剂，而且还是耐盐性的负调节剂。在发芽和幼苗发育的早期阶段，矮化突变体比野生型受盐胁迫的影响更小，同时与耐盐相关的基因上调更大，包括参与 ABA 生物合成、ABA 和 Ca2+ 信号传导的基因，以及阳离子交换剂和转运蛋白的编码。