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The plant-growth-promoting actinobacteria of the genus Nocardia induces root nodule formation in Casuarina glauca
Ist Teil von
Antonie van Leeuwenhoek, 2019-01, Vol.112 (1), p.75-90
Ort / Verlag
Cham: Springer International Publishing
Erscheinungsjahr
2019
Quelle
MEDLINE
Beschreibungen/Notizen
Actinorhizal plants form a symbiotic association with the nitrogen-fixing actinobacteria
Frankia
. These plants have important economic and ecological benefits including land reclamation, soil stabilization, and reforestation. Recently, many non-
Frankia
actinobacteria have been isolated from actinorhizal root nodules suggesting that they might contribute to nodulation. Two
Nocardia
strains, BMG51109 and BMG111209, were isolated from
Casuarina glauca
nodules, and they induced root nodule-like structures in original host plant promoting seedling growth. The formed root nodule-like structures lacked a nodular root at the apex, were not capable of reducing nitrogen and had their cortical cells occupied with rod-shaped
Nocardiae
cells. Both
Nocardia
strains induced root hair deformation on the host plant. BMG111209 strain induced the expression of the
ProCgNin
:Gus gene, a plant gene involved in the early steps of the infection process and nodulation development.
Nocardia
strain BMG51109 produced three types of auxins (Indole-3-acetic acid [IAA], Indole-3-Byturic Acid [IBA] and Phenyl Acetic Acid [PAA]), while
Nocardia
BMG111209 only produced IAA. Analysis of the
Nocardia
genomes identified several important predicted biosynthetic gene clusters for plant phytohormones, secondary metabolites, and novel natural products. Co-infection studies showed that
Nocardia
strain BMG51109 plays a role as a “helper bacteria” promoting an earlier onset of nodulation. This study raises many questions on the ecological significance and functionality of
Nocardia
bacteria in actinorhizal symbioses.