Signalling in actinorhizal root nodule symbioses
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Plants able to establish a nitrogen-fixing root nodule symbiosis with the actinobacterium Frankia are called actinorhizal. These interactions lead to the formation of new root organs, called actinorhizal nodules, where the bacteria are hosted intracellularly and fix atmospheric nitrogen thus providing the plant with an almost unlimited source of nitrogen for its nutrition. Like other symbiotic interactions, actinorhizal nodulation involves elaborate signalling between both partners of the symbiosis, leading to specific recognition between the plant and its compatible microbial partner, its accommodation inside plant cells and the development of functional root nodules. Actinorhizal nodulation shares many features with rhizobial nodulation but our knowledge on the molecular mechanisms involved in actinorhizal nodulation remains very scarce. However recent technical achievements for several actinorhizal species are allowing major discoveries in this field. In this review, we provide an outline on signalling molecules involved at different stages of actinorhizal nodule formation and the corresponding signalling pathways and gene networks.
KeywordsActinobacteria Biological nitrogen fixation Symbiosis Nodulation factors Nodulation Actinorhizal species Microbe-host signalling
We gratefully acknowledge support from IRD, CNRS (Project EC2CO), Genoscope, Genopole of Montpellier, and Agence Nationale de la Recherche (AN-06-BLAN-0095, BLAN 1708 01, 12-BSV7-0007-02) and United States Department of Agriculture (USDA NIFA 2015-67014-22849) and ECOS-SUD (A07B02 and A13B03).
VH, MN, ACM, PT, HG and SS wrote the manuscript. All the authors approved the paper.
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Conflict of interest
The authors have declared that no competing interest exists.
Human and animal rights
This article does not contain any studies with human participants or animals performed by any of the authors.
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