Researchers at Centro de Biotecnología y Genómica de Plantas (CBGP) have participated in the discovery of a new form of symbiotic association between an endophytic fungus and the model plant Arabidopsis thaliana.
This symbiosis promotes plant growth and can contribute to decreasing the use of inorganic fertilizers for a more sustainable agriculture.
Plants take advantage of mutualistic associations with different types of symbiotic fungi, such as mycorrhizas and endophytes. Mycorrhizal associations are among the best studied mutualisms because they are quite extended in the plant kingdom, and improve plants' ability to absorb phosphorous and other nutrients from soil.
There are some plant species, such as Arabidopsis thaliana and all the other species in the family Brassicaceae, that are not able to form mutualistic associations with mycorrhizas.
Soledad Sacristán and her team isolated the endophytic fungus Colletotrichum tofieldiae (Ct) from wild populations of A. thaliana in Spain. They discovered that Ct forms a natural mutualistic association with A. thaliana, since Arabidopsis plants inoculated with Ct produce more fruits and seeds than control plants.
In collaboration with researchers from Max Planck Institute of Plant Breeding Research in Germany, they have discovered that Ct infects the plants from the roots and is able to colonize the plant systemically. Ct transfers the macronutrient phosphorus to shoots, promoting plant growth and increasing fertility under phosphorus-deficient conditions.
The host phosphate starvation response (PSR) system controls Ct root colonization and is required for plant growth promotion (PGP). PGP also requires PEN2-dependent indole glucosinolate metabolism, a component of innate immune responses, indicating a functional link between innate immunity and the PSR system during beneficial interactions with Ct.
Ct is an endophytic fungus (fungus growing inside the plants without producing disease symptoms) very related with plant pathogens within the genus Colletotrichum. The nutrient status of the plant might have facilitated the transition from pathogenic to beneficial lifestyles of this fungus, which is in fact replacing the function of mycorrhizas in Arabidopsis.
Ct has been found in different parts of the world, but its association with A. thaliana seems to be endemic to Spain. Soledad Sacristán and her team have detected Ct with an incidence up to 50% in different wild populations of A. thaliana in Central Spain growing in phosphorous poor soils.
Original Paper: Hiruma, K; Gerlach, N; Sacristán, S; Nakano, Ryohei T; Hacquard, S; Kracher, B; Neumann, U; Ramírez, D; Bucher, M; O’Connell, Richard J; Schulze-Lefert, P. 2016. "Root endophyte Colletotrichum tofieldiae confers plant fitness benefits that are phosphate status dependent". Cell. DOI: 10.1016/j.cell.2016.02.028".