The effects of holoparasitism on plant organellar translation and tRNA metabolism

真核生物中的线粒体和叶绿体来源于细菌，它们保留了自己的基因组和蛋白质翻译的分子机制。这种翻译机制在植物中比在其他真核生物中更保守，更像细菌。为了验证与光合作用相关的蛋白质生产的强烈需求是保护植物线粒体和叶绿体翻译机制的自然选择的原因，该项目将研究全寄生植物的进化。这些生物完全失去了光合作用的能力，转而通过进入宿主植物的脉管系统或消耗土壤真菌来获取能量。许多基因已经从这些植物的细胞器基因组中丢失，这项研究将有助于理解即使经过数十亿年的进化分歧，细菌类酶如何在功能上被真核生物的同类酶所取代。此外，它将提供关于线粒体和叶绿体基因组中最后剩余基因如何丢失的见解，从而完成将这些细胞器整合到真核细胞中的最后步骤。该项目还将为生物信息学、分子遗传学、生物化学和进化生物学的本科生、研究生和博士后提供培训。它还将与国际合作、外展研讨会和一年级本科生项目相结合，以扩大计算生物学领域的就业机会。初步观察表明，全息寄生虫线粒体和叶绿体翻译机制的许多组成部分已经丢失，并在功能上被细胞质中相应的机制所取代，这些机制通常负责翻译由核基因编码的蛋白质。光合作用的丧失对细胞器翻译机制的干扰似乎与trna和氨基酰基trna合成酶（aaRSs）之间相互作用的广泛重新连接有关。这些变化将通过比较基因组学、亚细胞定位分析（荧光显微镜）、专门的tRNA测序方法和体外氨基酰化分析相结合来评估。这些分析将确定亚细胞靶向和aaRS底物特异性的变化在多大程度上促进了基因丢失和功能替代的过程。他们还将确定叶绿体tRNA-Glu在翻译和四吡咯生物合成中的平行作用如何在功能上被取代，从而导致该基因的丢失，并最终导致整个叶绿体基因组的丢失。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The mitochondria and chloroplasts found in eukaryotes are derived from bacteria and retain their own genomes and their own molecular machinery for protein translation. This translation machinery is more conserved and bacterial-like in plants than in other eukaryotes. To test the hypothesis that the intense demands for protein production associated with photosynthesis are responsible for the natural selection that conserves plant mitochondrial and chloroplast translation machinery, this project will investigate the evolution of holoparasitic plants. These organisms have entirely lost the ability to photosynthesize and instead acquire energy by tapping into the vasculature of a host plant or consuming soil fungi. Many genes have been lost from the organellar genomes of these plants, and this research will help understand how bacterial-like enzymes can be functionally replaced by their eukaryotic counterparts even after billions of years of evolutionary divergence. In addition, it will provide insights into how the very last remaining genes in mitochondrial and chloroplast genomes can be lost and thereby complete the final steps of integrating these organelles into the eukaryotic cell. The project will also provide training for researchers at undergraduate, graduate, and postdoctoral levels in bioinformatics, molecular genetics, biochemistry, and evolutionary biology. It will also be coupled with international collaborations, outreach workshops, and a program for first-year undergraduates to broaden access to career opportunities in computational biology.Initial observations indicate that numerous components of the mitochondrial and chloroplast translation machinery in holoparasites have been lost and functionally replaced with corresponding machinery from the cytosol that is typically responsible for translating proteins encoded by nuclear genes. The perturbations to organellar translation machinery resulting from loss of photosynthesis appear to be associated with extensive rewiring of interactions between tRNAs and aminoacyl-tRNA synthetases (aaRSs). These changes will be assessed through a combination of comparative genomics, subcellular localization analysis (fluorescence microscopy), specialized tRNA sequencing methods, and in vitro aminoacylation assays. These analyses will determine the extent to which changes in subcellular targeting and aaRS substrate specificity facilitate the process of gene loss and functional replacement. They will also determine how the well-characterized parallel roles of chloroplast tRNA-Glu in both translation and tetrapyrrole biosynthesis can both be functionally replaced, leading to the loss of this gene and eventually to the loss of the entire chloroplast genome.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.