In plants, Lipoxygenase (LOX) genes play crucial roles in tolerance to abiotic as well as biotic stress. Although they have been characterized in various plants, little is known about the evolution and role of LOX under high temperature, drought and their combination in Brassica. In this study, we identified 13 divergent LOX genes which are distributed among six linkage groups (LG) of Brassica rapa. These genes are unevenly distributed among all the three sub-genomes as moderately gene fractionized (MF1), most gene fractionized (MF2), and least gene fractionized (LF) with the differential loss and with the highest loss of genes on the LF. The substitution analysis (Ka/Ks) exhibited a signature of purifying selection of paralogous genes. Protein sequence analysis showed the presence of two canonical iron-binding signature regions along with PLAT/LH2 domain in all the identified LOX proteins indicating greater functional conservation. LOX expression pattern differed significantly under conditions of heat, drought and their combination which was also assessed by lipid peroxidation (MDA) assay and relative water content (RWC). Under heat stress, BraA.LOX5.a was found to be over expressed (6.16-fold) whereas under drought and combined stress, BraA.LOX2.a was identified as the major transcript with 15.76-fold over expression under drought and 18.67-fold under combined stress. These genes showed a significant positive correlation with biochemical stress indicator MDA. The 5′ upstream sequences of LOX genes were found to be highly divergent and showed the presence of different regulatory elements. This study provides a basis for conducting further characterization of stress-specific LOX protein and its involvement in stress-related signalling pathway.

中文翻译：

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油菜在高温、干旱和复合胁迫下脂肪氧化酶基因的进化和转录调控

在植物中，脂氧合酶 (LOX) 基因在对非生物和生物胁迫的耐受中起着至关重要的作用。尽管它们已在各种植物中得到表征，但对 LOX 在高温、干旱及其组合下在芸苔属植物中的进化和作用知之甚少。在这项研究中，我们确定了 13 个不同的 LOX 基因，它们分布在芸苔的六个连锁群 (LG) 中。这些基因在所有三个亚基因组中分布不均，如中度基因分离 (MF1)、大多数基因分离 (MF2) 和最少基因分离 (LF)，具有差异损失和 LF 上基因的最高损失。替代分析 (Ka/Ks) 表现出纯化选择旁系同源基因的特征。蛋白质序列分析表明，在所有鉴定的 LOX 蛋白中，存在两个典型的铁结合特征区域以及 PLAT/LH2 结构域，表明功能保守性更强。LOX 表达模式在高温、干旱及其组合条件下显着不同，这也通过脂质过氧化 (MDA) 测定和相对含水量 (RWC) 进行评估。在热胁迫下，发现 BraA.LOX5.a 过表达（6.16 倍），而在干旱和联合胁迫下，BraA.LOX2.a 被鉴定为主要转录物，在干旱下过表达 15.76 倍和 18.67 倍在综合压力下。这些基因与生化应激指标MDA呈显着正相关。发现 LOX 基因的 5' 上游序列高度分化，并显示存在不同的调控元件。该研究为进一步表征应激特异性LOX蛋白及其参与应激相关信号通路提供了基础。