Department of Biochemistry and Molecular Biology, Federal University of Ceara, 60455-760 Fortaleza, Ceará, Brazil.
J Plant Physiol. 2013 Dec 15;170(18):1609-19. doi: 10.1016/j.jplph.2013.06.012. Epub 2013 Jul 26.
In flowering plants, alternative oxidase (Aox) is encoded by 3-5 genes distributed in 2 subfamilies (Aox1 and Aox2). In several species only Aox1 is reported as a stress-responsive gene, but in the leguminous Vigna unguiculata Aox2b is also induced by stress. In this work we investigated the Aox genes from two leguminous species of the Medicago genus (Medicago sativa and Medicago truncatula) which present one Aox1, one Aox2a and an Aox2b duplication (named here Aox2b1 and Aox2b2). Expression analyses by semi-quantitative RT-PCR in M. sativa revealed that Aox1, Aox2b1 and Aox2b2 transcripts increased during seed germination. Similar analyses in leaves and roots under different treatments (SA, PEG, H2O2 and cysteine) revealed that these genes are also induced by stress, but with peculiar spatio-temporal differences. Aox1 and Aox2b1 showed basal levels of expression under control conditions and were induced by stress in leaves and roots. Aox2b2 presented a dual behavior, i.e., it was expressed only under stress conditions in leaves, and showed basal expression levels in roots that were induced by stress. Moreover, Aox2a was expressed at higher levels in leaves and during seed germination than in roots and appeared to be not responsive to stress. The Aox expression profiles obtained from a M. truncatula microarray dataset also revealed a stress-induced co-expression of Aox1, Aox2b1 and Aox2b2 in leaves and roots. These results reinforce the stress-inducible co-expression of Aox1/Aox2b in some leguminous plants. Comparative genomic analysis indicates that this regulation is linked to Aox1/Aox2b proximity in the genome as a result of the gene rearrangement that occurred in some leguminous plants during evolution. The differential expression of Aox2b1/2b2 suggests that a second gene has been originated by recent gene duplication with neofunctionalization.
在开花植物中，交替氧化酶（Aox）由分布在 2 个子家族（Aox1 和 Aox2）中的 3-5 个基因编码。在一些物种中，只有 Aox1 被报道为应激响应基因，但在豆科植物豇豆中，Aox2b 也受到应激诱导。在这项工作中，我们研究了来自 Medicago 属的两种豆科植物（紫花苜蓿和蒺藜苜蓿）的 Aox 基因，它们具有一个 Aox1、一个 Aox2a 和一个 Aox2b 重复（分别命名为 Aox2b1 和 Aox2b2）。在紫花苜蓿中的半定量 RT-PCR 表达分析表明，Aox1、Aox2b1 和 Aox2b2 转录本在种子萌发过程中增加。在叶片和根中进行的不同处理（SA、PEG、H2O2 和半胱氨酸）下的类似分析表明，这些基因也受到应激诱导，但具有特殊的时空差异。Aox1 和 Aox2b1 在对照条件下表达基础水平，并在叶片和根中受到应激诱导。Aox2b2 表现出双重行为，即在叶片中仅在应激条件下表达，并在根中表现出应激诱导的基础表达水平。此外，Aox2a 在叶片中的表达水平高于根中的表达水平，并且在根中似乎不受应激响应。从蒺藜苜蓿微阵列数据集获得的 Aox 表达谱也揭示了 Aox1、Aox2b1 和 Aox2b2 在叶片和根中的应激诱导共表达。这些结果强化了一些豆科植物中 Aox1/Aox2b 的应激诱导共表达。比较基因组分析表明，这种调节与基因组中 Aox1/Aox2b 的邻近性有关，这是由于进化过程中一些豆科植物中发生的基因重排所致。Aox2b1/2b2 的差异表达表明，第二个基因是由最近的基因复制产生的，并具有新功能化。
