Apple fruit is covered by cuticle wax, which plays important roles protecting fruits from adverse environmental conditions. β-Ketoacyl-CoA synthase (KCS) is the key rate-limiting enzyme in plant wax synthesis. In this study, we identified 28 KCS gene family members from apple (Malus × domestica Borkh.) by homology analysis. Multi-sequence alignment and phylogenetic analyses revealed that the 28 MdKCS genes were divided into four subgroups, including KCS1-like, FAE1-like, FDH-like, and CER6. A chromosomal localization analysis revealed that 27 apple KCS genes were located on 11 chromosomes, while MdKCS28 was localized to the unassembled genomic scaffold. Most of the MdKCS proteins were hydrophilic proteins and they had similar secondary and tertiary structures. The prediction of cis-acting elements of the MdKCS gene promoters suggested that the MdKCS genes may be widely involved in hormone signaling and the stress response. Furthermore, the quantitative real-time polymerase chain reaction results showed that eight MdKCS genes were highly expressed in the apple pericarp, and were significantly induced by drought, abscisic acid (ABA), and NaCl treatments. We transformed the MdKCS21 gene into apple calli, and found the MdKCS21 overexpressing transgenic apple calli exhibited higher tolerance to ABA treatment. Finally, the MdKCS proteins were localized to the endoplasmic reticulum and vacuolar membrane by confocal laser microscopy. This study established a foundation to further analyze the function of KCS genes and provided candidate genes for molecular improvement of wax content in apple.

中文翻译：

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苹果中MdKCS基因的全基因组分析和功能鉴定。

苹果果实被表皮蜡覆盖，该蜡起着保护水果免受不利环境条件的重要作用。β-酮酰基辅酶A合酶（KCS）是植物蜡合成中的关键限速酶。在这项研究中，我们通过同源性分析从苹果（Malus×domestica Borkh。）中鉴定了28个KCS基因家族成员。多序列比对和系统发育分析表明，将28个MdKCS基因分为四个亚组，包括KCS1样，FAE1样，FDH样和CER6。染色体定位分析显示27个苹果KCS基因位于11条染色体上，而MdKCS28定位在未装配的基因组支架上。大多数MdKCS蛋白是亲水蛋白，它们具有相似的二级和三级结构。MdKCS基因启动子的顺式作用元件的预测表明，MdKCS基因可能广泛参与激素信号传导和应激反应。此外，实时定量聚合酶链反应的定量结果表明，八个MdKCS基因在苹果果皮中高表达，并受到干旱，脱落酸（ABA）和NaCl处理的明显诱导。我们将MdKCS21基因转化为苹果愈伤组织，发现过表达MdKCS21的转基因苹果愈伤组织对ABA处理表现出更高的耐受性。最后，通过共聚焦激光显微镜将MdKCS蛋白定位于内质网和液泡膜。该研究为进一步分析KCS基因的功能奠定了基础，并为提高苹果中蜡含量的分子水平提供了候选基因。