ICAR-National Institute for Plant Biotechnology, Pusa Campus, New Delhi, 110012, India.
Plant Mol Biol. 2021 May;106(1-2):109-122. doi: 10.1007/s11103-021-01132-0. Epub 2021 Feb 27.
Recombinations between the parental genomes produced a novel mitochondrial genome in the cytoplasmic male sterile Brassica juncea cybrid Og1. A mitochondrial stoichiometric shift greatly reduced the molecule containing male-sterility-inducing orf138 gene leading to reversion to male fertility. An improved, chlorosis-corrected, cytoplasmic male sterile Brassica juncea cybrid Og1 derived from Ogura cytoplasm shows frequent reversion to male fertility. To determine the nature of mitochondrial recombination in the cybrid and to uncover the molecular mechanism of male fertility reversion, we sequenced the mitochondrial genomes of Og1, its isonuclear parental lines (OgRLM and Brassica juncea RLM198) and the revertant line (Og1-rt). Assembly of Og1 mitochondrial genome gave two circular molecules, Og1a (250.999 kbp) and Og1b (96.185 kbp) sharing two large direct repeat regions capable of recombining to form a single circular molecule. Og1a contains all essential mitochondrial genes, but the male-sterility-causing orf138 was uniquely present in Og1b along with 16 other complete or partial genes already represented in Og1a. Eleven and four recombinations between the parental mitochondrial genomes produced the Og1a and the Og1b molecules, respectively. Five genes were duplicated within Og1a, of which trnfM was inherited from both the parents while the other four genes, atp4, cox1 nad4L and trnM, were inherited from RLM198. RFLP analysis revealed that orf138-containing molecules were less abundant than Og1a in the male-sterile plants while og1b bearing molecules were undetectable in the revertant line. However, orf138 transcripts were amplified in RT-PCR and were also detected in northern blots revealing that Og1b molecules are not completely lost in the revertant plants. This is the first report where the mitochondrial genome of a cybrid is compared with its actual parents. The findings are discussed in the light of previous reports on mitochondrial genome recombination in cybrids.
甘蓝型油菜细胞质雄性不育恢复系 Og1 是双亲基因组重组产生的新型线粒体基因组。线粒体化学计量的变化极大地减少了含有雄性不育诱导基因 orf138 的分子，导致雄性育性恢复。源自 Ogura 细胞质的改良、褪绿症校正的、胞质雄性不育甘蓝型油菜杂种 Og1 经常发生雄性育性恢复。为了确定杂种中线粒体重组的性质，并揭示雄性育性恢复的分子机制，我们对 Og1、其同核亲本系（OgRLM 和甘蓝型油菜 RLM198）和回复系（Og1-rt）的线粒体基因组进行了测序。Og1 线粒体基因组的组装产生了两个圆形分子，Og1a（250.999 kbp）和 Og1b（96.185 kbp），它们共享两个能够重组形成单个圆形分子的大型直接重复区。Og1a 包含所有必需的线粒体基因，但引起雄性不育的 orf138 仅存在于 Og1b 中，同时还有 16 个其他完整或部分基因已经存在于 Og1a 中。11 次和 4 次父母线粒体基因组之间的重组分别产生了 Og1a 和 Og1b 分子。Og1a 内有 5 个基因重复，其中 trnfM 来自双亲，而其他 4 个基因，atp4、cox1、nad4L 和 trnM，来自 RLM198。RFLP 分析显示，在雄性不育植物中，含有 orf138 的分子比 Og1a 少，而在回复系中，没有检测到携带 og1b 的分子。然而，在 RT-PCR 中扩增了 orf138 的转录物，并在 northern blot 中也检测到了它们，这表明在回复系植物中，Og1b 分子并没有完全丢失。这是首次比较杂种的线粒体基因组与其实际父母的报告。根据以前关于杂种中线粒体基因组重组的报告，讨论了这些发现。
