About this Research Topic
Nitrogen fixing rhizobial-plant interaction is one of the most remarkable examples of symbiosis. This interaction involves plants (Leguminosae) and bacterial partners (called rhizobia) of Alphaproteobacteria and Betaproteobacteria classes. More than 128 species of rhizobia are known, belonging to 13 genera, which establish symbiosis with important crop plants (as forage and grain legumes).
After a complex signalling dialogue between plants and bacteria allowing the colonisation of root tissues, bacterial physiology undergoes to a drastic remodelling in order to perform the reduction of atmospheric nitrogen to ammonia. In this process plants develop root nodules in which bacteria multiply and differentiate in nitrogen fixing cells. In recent years a number of new discoveries have emerged. The discovery of defensin-like peptides called "nodule-specific cysteine-rich" (NCR) peptides showed that legumes have evolved signals to control the bacterial infection. Also the molecular dissection of rhizobial cell cycle control has shed light into the bacterial differentiation inside plant tissue. However, a number of questions are still unanswered. In particular, what is the role of NCR in bacterial metabolism and cell cycle control? What are the molecular bases and evolutionary consequences of bacterial partner choice operated by the host plant? Is there and which role may have the presence of a non-symbiotic rhizobia in the soil in the plant rhizosphere and endosphere? Finally, which are the selective forces shaping rhizobial genomic diversity and the evolution of multipartite rhizobial genomes? A better comprehension of such molecular and ecological connections between rhizobia and plants represents one of the present-day challenges of the plant-microbe interaction research. This knowledge may open new frontiers for the biotechnological exploitation of the rhizobial symbiosis in sustainable agriculture and in the discovery of new ways to control bacterial colonization of eukaryotic hosts.
Keywords: rhizobia, symbiotic nitrogen fixation, plant-microbe interaction, rhizosphere, root nodule
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