Symbiosis and Plant Genomics Group

Research

Climate change, environmental pollution, the energy crisis, food security and pandemics are among the biggest societal challenges nowadays. One of the greatest tasks to be solved in our time is how to feed the world with environmentally friendly way. The use of nitrogen fertilizers multiplied the agricultural productivity which led to the explosion of the human population. On the other hand, the excess use of fertilizers seriously polluted the environment and greatly triggers the climate change. Biological nitrogen fixation has no negative impact on the environment and has the potential to contribute to a sustainable agriculture and health of plants, animals, and humans. The most efficient form of biological nitrogen fixation occurs in the symbiosis of legume plants and Rhizobium bacteria.

Legumes compose the third largest family of flowering plants. Medicago truncatula and other leguminous plants are able to establish nitrogen-fixing symbiotic associations with specialized soil bacteria belonging to the genus rhizobia. This symbiotic interaction accounts for a significant proportion of biological nitrogen fixation worldwide.

Symbiotic nitrogen fixation takes place in specialized organs on the root, termed nodules wherein rhizobia convert atmospheric nitrogen to ammonia that is assimilated by the host plant. Nodule formation is a result of several consecutive communication steps between the plant and the bacteria. Nod factors (NF) produced by the bacteria are essential signaling components to establish the symbiotic interaction. The recognition of compatible rhizobia in root hair cells induces two related developmental processes, the rhizobia infection and cortical cell division, which result in the formation of the symbiotic nodules on legume roots. Rhizobia are hosted in symbiosomes in the cytoplasm of infected nodule cells. The symbiosome is the site of nitrogen fixation and functions in nutrient and signal exchange between the two symbionts. The bacteria undergo morphological changes and metabolic differentiation in symbiosomes to transform into their symbiotic state termed bacteroids. The bacteroid differentiation is an irreversible transition in nodules of M. truncatula and closely related legumes and it is directed by a large family of nodule-specific cysteine-rich peptides (NCRs) produced by the host plant.

The research of our group focuses on the agriculturally and environmentally important symbiotic association between leguminous plants and rhizobia. One aim of our research is to reveal the molecular steps of nodule initiation, bacterial invasion and nodule function to better understand the molecular basis of symbiotic nitrogen fixation. We use state-of-the-art molecular, genomic and biochemical methods to identify and characterize symbiotic genes, identify interacting partners and regulation mechanisms that are important during the symbiotic interaction. Soil microbiomes contain hundreds of eligible rhizobia strains possessing the necessary toolkit to establish effective nitrogen-fixing symbiosis with legumes growing in the habitat. Thus, the plants have to make their choice using mechanisms other than the basic toolkit to select their bacterial partners. Our second research interest is, which plant genes/proteins are responsible for the partner selection and which bacterial genes/proteins make a rhizobia preferable or unacceptable for the plant. The aim of the study of NCR peptides is to identify their bacterial targets and reveal the exact role of NCR peptides during nitrogen-fixing symbiosis. Beyond their symbiotic action, cationic NCRs have strong antimicrobial effects on a wide variety of bacteria and fungi. Another focus of our research is to identify the action of cationic NCRs and study their potential medical or agronomical application.