Actinorhizal plant

Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinomycetota Frankia.

Their symbiotic relationships with Frankia evolved independently over time,[3] and the symbiosis occurs in the root nodule infection site.

[7] Other species of actinorhizal plants are common in temperate regions like alder, bayberry, sweetfern, avens, mountain misery and coriaria.

Their ability to form nitrogen-fixing nodules confers a selective advantage in poor soils, and are therefore pioneer species where available nitrogen is scarce, such as moraines, volcanic flows or sand dunes.

The genetic program used to establish the symbiosis has probably recruited elements of the arbuscular mycorrhizal symbioses, a much older and widely distributed symbiotic association between plants and fungi.

In this case the infection begins with an intracellular penetration of a Frankia hyphae root hair, and is followed by the formation of a primitive symbiotic organ known as a prenodule.

In both cases the infection leads to cell divisions in the pericycle and the formation of a new organ consisting of several lobes anatomically similar to a lateral root.