Sequence adaptation of Symbiosis Receptor-like Kinase (SymRK) enabling nitrogen-fixing root nodule development

新特征进化的基础上的分子创新是生物多样性的驱动力。这些驱动程序的识别为综合安装或优化这一特性提供了路线图中的里程碑。最早的陆地植物化石带有丛枝菌根(AM)的结构，这种结构与提供营养的真菌共生，而大多数今天的陆地植物仍然参与这种共生。相比之下，根瘤共生(RNS)与固氮菌的共生要年轻得多，仅限于一个由四个目的植物组成的门，即Fabales、Fagales、Cucurbitales和Rosales。AM真菌细胞内适应的遗传工具包在陆地植物中很大程度上是保守的。在RNS的进化过程中，它的一部分被增选，包括一系列信号转导组件，如共生受体样激酶(SymRK)。我们获得的证据表明，在进化过程中，SymRK经历了超功能化；它获得了新的分子特征，促进了RNS的发展，同时保持了其对AM的保守功能在这个项目中，我们将探索SymRK同源物之间的氨基酸序列多样性，目的是确定植物细胞根瘤菌感染的关键序列适应。我们将在细胞和分子水平上研究这些序列变异的机制后果，特别是SymRK蛋白相互作用组。解开由这些适应调控的蛋白质-蛋白质相互作用将精确定位促进固氮菌共生感染植物细胞过程的特定机制创新。

Molecular innovations underlying the evolution of novel traits are the drivers of biological diversification. The identification of these drivers provides the milestones within a roadmap to synthetically install or optimize this trait. Fossils of the earliest land plants carry structures of arbuscular mycorrhiza (AM), a symbiosis with nutrient-delivering fungi that most present day land plants still engage in. In contrast, the root nodule symbiosis (RNS) with nitrogen-fixing bacteria is much younger, and restricted to a single phylum comprising four orders of plants, the Fabales, Fagales, Cucurbitales and Rosales. The genetic toolkit underlying the intracellular accommodation of AM fungi is largely conserved across land plants. Parts of it have been co-opted during the evolution of RNS, including a set of signal transduction components such as the Symbiosis Receptor-like Kinase (SymRK). We obtained evidence that during evolution, SymRK underwent super-functionalization; it acquired novel molecular features that facilitated the development of RNS, while maintaining its conserved function for AM. In this project, we will explore the amino acid sequence diversity among SymRK orthologs with the goal to identify critical sequence adaptations that underlie the rhizobial infection of plant cells. We will study the mechanistic consequences of these sequence variations at the cellular and molecular level with a special focus on the SymRK protein interactome. Unravelling protein-protein interactions modulated by these adaptations will pinpoint the specific mechanistic innovations facilitating the symbiotic infection process of plant cells by nitrogen-fixing bacteria.