Live-tracking rhizobial switch from rhizosphere to plant-confined colonization modes

豆科植物与根瘤菌建立了有益的固氮共生关系，根瘤菌在被称为根瘤的特殊根器官中为植物提供氮。这种相互作用的早期阶段需要在宿主植物重新编程细菌根进入之前在根际进行关键的分子交换。虽然大多数根瘤菌物种通过新形成的根毛细胞质外体隔室（称为感染线（IT））感染宿主的根部，但其他根瘤菌通过替代和较少研究的细胞间感染模式在宿主植物上定居。在这两种情况下，根瘤菌必须从根际转换到感染状态，在那里它们被限制在植物质外体区室中。到目前为止，在早期感染期间研究植物局限环境中的细菌重编程在技术上具有挑战性，因为这些事件仅限于少数根细胞。Live-Switch是一个创新的项目，旨在解决关键的，但在很大程度上尚未探索的问题，根瘤菌如何科普急剧转变，从自由生活到感染性的宿主内状态。该项目将利用建立细胞内或细胞间感染模式的苜蓿和莲花模式豆科植物系统，在单细胞水平上破译根瘤菌细胞如何在从自由生活到宿主限制环境的转换过程中重新编程。该项目将结合联合收割机活细胞成像和突变体分析的细菌和植物的合作伙伴，剖析根瘤菌的信号产生，细胞增殖和运动的动态和串扰与植物的合作伙伴。在最终的数学模型中的数据的整合将允许更好地了解根瘤菌在植物IT隔间的传播和增殖的动态。Live-Switch依赖于法国和德国团队之间理想的集成和协作框架，凭借他们在植物和细菌合作伙伴的分子和细胞生物学方面的坚实和互补的专业知识，将能够解决动态环境如何塑造细菌重编程到植物生活方式的体内转换的令人兴奋的问题。

Legumes establish beneficial nitrogen-fixing symbioses with rhizobia bacteria that supply nitrogen for the plant within specialized root organs, known as nodules. Early stages of this interaction require crucial molecular exchanges in the rhizosphere before the host plant reprograms for bacterial root entry. While most rhizobia species infect the roots of their host via a newly formed root hair intracellular apoplastic compartment called infection thread (IT), others colonize their host plants via alternative and less studied intercellular infection modes. In both cases, rhizobia must switch from a rhizospheric to an infecting state where they become confined within plant apoplastic compartments. Up to now, it has been technically challenging to study bacterial reprogramming within plant-confined environments during early infection, as these events are restricted to a few root cells. Live-Switch is an innovative project aimed at addressing the crucial but largely unexplored question of how rhizobia cope with the drastic transition from free living to infective within-host state. The project will take advantage of Medicago and Lotus model legume systems establishing intracellular or intercellular infection modes, to decipher at the single cell level how rhizobia cells reprogram during the switch from a free-living to a host-confined environment. The project will combine live cell imaging and mutant analyses of both bacteria and plant partners to dissect the dynamics of rhizobial signal production, cell proliferation and motility and the cross talk with the plant partner. The integration of data in a final mathematical model will permit a better understanding of the dynamics of spreading and proliferation of rhizobia in the in planta IT compartment. Live-Switch relies on an ideal integrated and collaborative frame between the French and German groups, that with their solid and complementary expertise in molecular and cell biology of both plant and bacteria partners, will be able to address the exciting question of how dynamic environments shape the in vivo switch of bacterial reprograming to in planta lifestyles.