Sun Feng, Zhang Xiaoyan, Shen Yun, Wang Hongchun, Liu Rui, Wang Xiaomin, Gao Dahai, Yang Yan-Zhuo, Liu Yiwei, Tan Bao-Cai
Key Laboratory of Plant Development and Environmental Adaptation Biology, Ministry of Education, School of Life Sciences, Shandong University, Qingdao, 266237, China.
Key Laboratory of Cell Activities and Stress Adaptations, Ministry of Education, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
Plant J. 2018 Jul 12. doi: 10.1111/tpj.14030.
Splicing of plant organellar group II introns is under accurate nuclear control that employs many nucleus-encoded protein cofactors from various families. For mitochondrial introns, only a few splicing factors have been characterized because disruption of their functions often causes embryo lethality. Here, we report the function of Empty Pericarp8 (Emp8) in the splicing of three group II introns in mitochondria, complex I biogenesis, and seed development in maize. Emp8 encodes a P subfamily pentatricopeptide repeat protein that localizes in mitochondria. The loss-of-function mutants of Emp8 are embryo lethal, showing severely arrested embryo and endosperm development in maize. The respiration rate in the emp8 mutants is reduced with substantially enhanced expression of alternative oxidases. Transcript analysis indicated that the trans-splicing of nad1 intron 4 and cis-splicing of nad4 intron 1 are abolished, and the cis-splicing of nad2 intron 1 is severely impaired in the emp8 mutants. These defects consequently lead to the disassembly of mitochondrial complex I and a dramatic reduction in its activity. Together, these results suggest that Emp8 is required for the trans-splicing of nad1 intron 4 and cis-splicing of nad4 intron 1 and nad2 intron 1, which is essential to mitochondrial complex I assembly and hence to embryogenesis and endosperm development in maize.
植物细胞器II类内含子的剪接受到精确的核控制，该控制利用了来自不同家族的许多核编码蛋白辅助因子。对于线粒体内含子，只有少数剪接因子得到了表征，因为它们功能的破坏通常会导致胚胎致死。在这里，我们报道了空果皮8（Emp8）在玉米线粒体中3个II类内含子的剪接、复合体I的生物发生以及种子发育中的功能。Emp8编码一种定位于线粒体的P亚家族五肽重复蛋白。Emp8的功能缺失突变体胚胎致死，在玉米中表现出胚胎和胚乳发育严重停滞。emp8突变体的呼吸速率降低，交替氧化酶的表达大幅增强。转录本分析表明，emp8突变体中nad1内含子4的反式剪接和nad4内含子1的顺式剪接被消除，nad2内含子1的顺式剪接严重受损。这些缺陷最终导致线粒体复合体I的解体及其活性的显著降低。总之，这些结果表明Emp8是nad1内含子4的反式剪接以及nad4内含子1和nad2内含子1的顺式剪接所必需的，这对线粒体复合体I的组装至关重要，因此对玉米的胚胎发生和胚乳发育也至关重要。
