Actinorhizal Plant Root Exudates Alter the Physiology, Surface Properties, and Plant Infectivity of Frankia


Members of the genus Frankia are soil-dwelling actinobacteria distinguished by their ability to form symbiotic nitrogen-fixing associations with eight different families of angiosperm plants. The initial molecular interactions between Frankia and its host plants in the soil are poorly understood. With the Rhizobium-legume associations, root exudates are important in the communication step between the microbe and plant host. Here we describe a study, based on (Beauchemin NJ, Furnholm T, Lavenus J, Svistoonoff S, Domumas P, Bogusz D, Laplaze L, Tisa LS. 2012. Casuarina root exudates alter the physiology, surface properties, and plant infectivity of Frankia sp. Strain CcI3. Appl. Environ. Microbiol. 78: 575580.), that investigates the effects of host plant root exudates on Frankia physiology and plant-microbe interactions. Aqueous root exudates were collected from actinorhizal plants under nitrogen-sufficient and – deficient conditions and tested on Frankia strains. Root exudates alone were unable to support Frankia sp. strain CcI3 growth, but growth yield increased in the presence of root exudates and a carbon source. The addition of plant root exudates caused a hyphal curling effect that was host-specific, but age-independent. Root exudates from both plants grown plants under nitrogen-sufficient and – deficient conditions elucidated this response. The surface properties of root exudates treated Frankia were altered at the fatty acid levels as determined by reduced Congo red dye binding. Fourier transform infrared spectroscopy (FTIR) confirmed the fatty acid changes and also showed changes in carbohydrate content. Analysis of other Frankia strains also showed host-plant-specific hyphal curling response to root exudates. Frankia sp. strain CcI3 pre-exposed to plant root exudates initiated the onset of nodulation on the host plants earlier than control cells. Preliminary results with other Frankia strains confirm these results. These results indicate the presence of an early signaling event between actinorhizal host plants and Frankia in the soil.


Molecular, Cellular and Biomedical Sciences

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Biological Nitrogen Fixation



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Book Chapter


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