A homologous gene of strigolactones repressor protein gene SMXL7/D53, MdSMXL8.2 (GenBank accession No.: MD07G1222400), was cloned from ‘Royal Gala’ apple (Malus × domestica Borkh.) in this study. The sequence analysis revealed that the length of this gene was 3 243 bp, which encoded 1 080 amino acids, and had a protein molecular mass of ∼110 kD. The phylogenetic tree analysis indicated that the MdSMXL8.2 exhibited the highest sequence similarity with Arabidopsis AtSMXL7. The protein conserved domain analysis revealed that the MdSMXL8.2 contained two ClpA domains. The prediction of the secondary and tertiary structures of the MdSMXL8.2 indicated that it contained 34.54% α helix, 3.43% β-sheet, and 11.76% extended chain. The in-silico analysis suggested that the promoter sequence of MdSMXL8.2 contained several typical cis-acting elements, including abscisic acid (ABA), gibberellin (GA), ethylene, auxin, jasmonic acid (JA), salicylic acid (SA), drought, and heat stress-responsive elements. Quantitative real-time (qRT)-PCR analyses revealed that MdSMXL8.2 was expressed in different apple tissues, with the highest transcript level found in the stem. The expression of MdSMXL8.2 was significantly induced by exogenous ABA, PEG and mannitol, while exogenous NaCl significantly inhibited MdSMXL8.2 expression. The growing status of MdSMXL8.2-overexpressed Orin apple callus was worse than the wild type (WT) after NaCl treatment and had a higher malondialdehyde (MDA) content and relative conductance (REC). Additionally, MdSMXL8.2-overexpressed Arabidopsis exhibited shorter root length and a reduction in fresh weight under salt stress, indicating that MdSMXL8.2 negatively regulated salt tolerance in apples.

本研究从'Royal Gala'苹果( Malus  ×  domestica Borkh.)中克隆了独脚金内酯抑制蛋白基因SMXL7/D53的同源基因MdSMXL8.2 (GenBank登录号：MD07G1222400) 。序列分析表明，该基因全长3 243 bp，编码1 080个氨基酸，蛋白质分子量约110 kD。系统发育树分析表明，MdSMXL8.2 与拟南芥AtSMXL7表现出最高的序列相似性。蛋白质保守域分析显示 MdSMXL8.2 包含两个 ClpA 域。MdSMXL8.2 二级和三级结构的预测表明它含有 34.54% 的α螺旋、3.43% 的β-折叠和 11.76% 的延伸链。这计算机分析表明MdSMXL8.2的启动子序列含有几种典型的顺式作用元件，包括脱落酸（ABA）、赤霉素（GA）、乙烯、生长素、茉莉酸（JA）、水杨酸（SA）、干旱, 和热应力响应元件。定量实时 (qRT) -PCR分析显示MdSMXL8.2在不同的苹果组织中表达，在茎中发现的转录水平最高。MdSMXL8.2的表达受外源性ABA、PEG和甘露醇显着诱导，而外源性NaCl显着抑制MdSMXL8.2的表达。MdSMXL8.2的成长状况-过表达的 Orin 苹果愈伤组织在 NaCl 处理后比野生型 (WT) 更差，并且具有更高的丙二醛 (MDA) 含量和相对电导 (REC)。此外，过表达MdSMXL8.2 的拟南芥在盐胁迫下表现出较短的根长和鲜重减少，表明MdSMXL8.2对苹果的耐盐性负调节。