Functional Analysis of PPR-SMR-related Proteins in Zea mays (Maize) and Arabidopsis thaliana

质体基因的表达对质体的所有代谢过程和植物的生存都至关重要。质体基因表达的调控发生在不同水平的转录、转录成熟和蛋白质组装过程中。调控质体基因表达需要多种核编码因子。五肽重复（PPR）蛋白似乎起着特别重要的作用，并参与许多类型的RNA代谢。在我的博士工作中，我发现了一种新型的PPR蛋白，其特征是第二个功能基序称为SMR（小mts相关）。含有PPR和SMR结构域的蛋白质在PPR大家族中构成一个小的“亚家族”。SMR结构域已被证明具有切口内切酶活性。这一点，再加上目前对PPR基序的了解，表明PPR- smr亚家族可能作为核酸内切酶参与DNA或RNA代谢、DNA修复、转录和/或翻译过程。在本项目中，我将通过研究四种在玉米中预测的质体PPR-SMR蛋白和拟南芥中的同源蛋白来探索这些可能性；这两种生物的使用将是协同的，因为它们各自提供不同的实验优势。工作将包括确定特定的核酸靶序列、核酸内切酶测定和比较表型、玉米和拟南芥突变体的分子和生化分析。我将确定每种蛋白质在体内是否与特定的RNA和/或DNA序列相互作用，以及在突变背景下相应核酸的代谢是否被破坏。

Plastid gene expression is essential for all metabolic processes in plastids and for plant viability. The regulation of plastid gene expression occurs at various levels of transcription, transcript maturation and protein assembly processes. Numerous nucleus encoded factors are needed for the regulation of plastid gene expression. Pentatricopeptide repeat (PPR) proteins appear to play a particularly important role, and participate in many types of RNA metabolism. In my Ph.D. work, I identified a novel type of PPR protein that is characterized by a second functional motif called SMR (small MutS-releated). Proteins harboring both PPR and SMR domains comprise a small ¿subfamily¿ within the large PPR family. The SMR domain has been shown to have nicking endonuclease activity. This, together with current understanding of PPR motifs, suggests that the PPR-SMR subfamily may participate in DNA or RNA metabolism, DNA repair, transcriptional and/or translational processes by acting as endonucleases. In this project I will explore these possibilities by studying four predicted plastid PPR-SMR proteins in Zea mays (maize) and the orthologous proteins in Arabidopsis; use of the two organisms will be synergistic as they each offer different experimental advantages. Work will include determinations of specific nucleic acid target sequences, endonuclease assays and comparative phenotypic, molecular and biochemical analyses of mutants in maize and Arabidopsis. I will determine whether each protein interacts with specific RNA and/or DNA sequences in vivo, and whether the metabolism of the corresponding nucleic acids is disrupted in the mutant background.