Actinorhizal plants can establish an ecologically important symbiosis that leads to the development of nitrogen‐fixing nodules in response to the soil actinobacteria Frankia.
Actinorhizal root nodulation following intracellular infection by Frankia is a multistep process involving both plant and Frankia specific signals that activate a symbiotic signaling pathway. Flavonoids have been shown to improve the nodulation process and to be necessary for root hair infection, and ongoing research efforts focus on the biochemical characterization of Frankia signals. With the development of RNA interference to knock down candidate symbiotic genes in the actinorhizal plants Casuarina glauca and Datisca glomerata, plant genes essential for both infection, nodule formation and endomycorrhization have been characterized. Data provide evidence that there are some similarities in the molecular mechanisms underlying the nodulation process by Frankia and rhizobia.