A new form of plant-microorganism symbiosis discovered at CBGP

Researchers at CBGP have participated in the discovery of a new form of symbiotic association between an endophytic fungus and the model plant Arabidopsis thaliana, published today in the journal Cell.

The team of the researcher Soledad Sacristán, at the Centre for Plant Biotechnology and Genomics (CBGP (UPM-INIA)) at Universidad Politécnica de Madrid (UPM), has collaborated with theMax Planck Institute of Plant Breeding Research at Germany, in the publication today in Cell showing, for the first time, the symbiotic association between the Brassicaceae species Arabidopsis thaliana and the endophytic fungus Colletotrichum tofieldiae. This new discovered symbiosis promotes plants growth and can contribute to decrease 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. Despite the important function of mycorrhizas, 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 at CBGP 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.

Image: Arabidopsis thaliana plants inoculated with C. tofieldiae (right) and mock inoculated (left) growing in low phosphate conditions. Source: Cell.

Ct is an endophytic fungus (fungus growing inside the plants without producing diseasesymptoms) 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.

Soledad Sacristán carries out her research within the group “Plant Innate Immunity and Resistance against Necrotrophic Fungi ” led by Professor Antonio Molina , at the CBGP, where she is responsible of the research line “Ecological and molecular factors involved in endophytism and pathogenesis in fungi”.

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".

Imagen: GFP labelled Colletotrichum tofieldiae hyphae penetrating penetrating PIP2A-mCherry-labeled A. thaliana roots. Source: Cell