State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Taian, Shandong, 271018, PR China.
Institute of Molecular Breeding for Maize, Qilu Normal University, Jinan, 250200, PR China.
BMC Plant Biol. 2020 Dec 9;20(1):553. doi: 10.1186/s12870-020-02765-x.
Pentatricopeptide repeat (PPR) proteins compose a large protein family whose members are involved in both RNA processing in organelles and plant growth. Previous reports have shown that E-subgroup PPR proteins are involved in RNA editing. However, the additional functions and roles of the E-subgroup PPR proteins are unknown.
In this study, we developed and identified a new maize kernel mutant with arrested embryo and endosperm development, i.e., defective kernel (dek) 55 (dek55). Genetic and molecular evidence suggested that the defective kernels resulted from a mononucleotide alteration (C to T) at + 449 bp within the open reading frame (ORF) of Zm00001d014471 (hereafter referred to as DEK55). DEK55 encodes an E-subgroup PPR protein within the mitochondria. Molecular analyses showed that the editing percentage of 24 RNA editing sites decreased and that of seven RNA editing sites increased in dek55 kernels, the sites of which were distributed across 14 mitochondrial gene transcripts. Moreover, the splicing efficiency of nad1 introns 1 and 4 and nad4 intron 1 significantly decreased in dek55 compared with the wild type (WT). These results indicate that DEK55 plays a crucial role in RNA editing at multiple sites as well as in the splicing of nad1 and nad4 introns. Mutation in the DEK55 gene led to the dysfunction of mitochondrial complex I. Moreover, yeast two-hybrid assays showed that DEK55 interacts with two multiple organellar RNA-editing factors (MORFs), i.e., ZmMORF1 (Zm00001d049043) and ZmMORF8 (Zm00001d048291).
Our results demonstrated that a mutation in the DEK55 gene affects the mitochondrial function essential for maize kernel development. Our results also provide novel insight into the molecular functions of E-subgroup PPR proteins involved in plant organellar RNA processing.
五肽重复（PPR）蛋白组成了一个庞大的蛋白质家族，其成员参与细胞器中的 RNA 加工和植物生长。先前的报告表明，E 亚组 PPR 蛋白参与 RNA 编辑。然而，E 亚组 PPR 蛋白的其他功能和作用尚不清楚。
本研究开发并鉴定了一个新的玉米籽粒突变体，其胚胎和胚乳发育受阻，即缺陷型籽粒（dek）55（dek55）。遗传和分子证据表明，缺陷型籽粒是由于在开放阅读框（ORF）内 +449bp 处的单核苷酸改变（C 到 T）引起的Zm00001d014471（以下称为 DEK55）。DEK55 编码线粒体中的 E 亚组 PPR 蛋白。分子分析表明，dek55 籽粒中 24 个 RNA 编辑位点的编辑百分比降低，7 个 RNA 编辑位点的编辑百分比增加，这些位点分布在 14 个线粒体基因转录本中。此外，与野生型（WT）相比，dek55 中 nad1 内含子 1 和 4 以及 nad4 内含子 1 的剪接效率显著降低。这些结果表明，DEK55 在多个位点的 RNA 编辑以及 nad1 和 nad4 内含子的剪接中发挥关键作用。DEK55 基因的突变导致线粒体复合物 I 功能失调。此外，酵母双杂交试验表明，DEK55 与两个多细胞器 RNA 编辑因子（MORFs），即 ZmMORF1（Zm00001d049043）和 ZmMORF8（Zm00001d048291）相互作用。
我们的研究结果表明，DEK55 基因突变影响玉米籽粒发育所必需的线粒体功能。我们的研究结果还为 E 亚组 PPR 蛋白参与植物细胞器 RNA 加工的分子功能提供了新的见解。
