Azolla: A Model System for Symbiotic Nitrogen Fixation and Evolutionary Developmental Biology



The water fern Azolla is remarkable in many respects. It has a rapid growth rate and is utilized in agriculture as fodder and fertilizer. From a biologist’s perspective, however, its most prominent feature rests within its leaflets. Within each Azolla leaflet, there is a cavity in which a nitrogen-fixing cyanobiont dwells – Nostoc azollae. This cyanobiont has been vertically inherited for more than 50 million years. Hence, coevolutionary forces have shaped the inner workings of both partners. While the symbiosis has been studied intensively for decades, in recent years, molecular characterization of the plant biology of Azolla has accelerated. This chapter summarizes developments in the study of Azolla. We set current knowledge of this symbiosis in context with advances in other nitrogen-fixing symbioses and more recent molecular data on the relationship between N. azollae and its host. Further, we discuss how environmental factors such as biotic and abiotic stresses could influence the cross-communication between Azolla and the cyanobiont and, finally, why Azolla is an up-and-coming model species for evolutionary and developmental analyses. We highlight its properties as a lab model system and review the recent molecular and (functional) genomic characterization of this one-of-a-kind water fern.


Azolla Cyanobacteria Evo-devo Plant-microbe interaction symbiosis Phytohormones 



Abscisic acid






Denaturing gradient gel electrophoresis






Hormogonia-inducing factor


Indole-3-acetic acid


International Rice Research Institute


Jasmonic acid




Microbial-associated molecular patterns


Receptor-like kinase


Salicylic acid





JdV thanks the German Research Foundation (DFG) for a Research Fellowship (VR132/1-1). SdV gratefully acknowledges support through a Killam Postdoctoral Fellowship. We thank John Archibald for many useful and helpful comments on the manuscript.


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© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Biochemistry and Molecular BiologyDalhousie UniversityHalifaxCanada

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