Identifying the role of nodule endophytes in shaping nitrogen fixation effectiveness

• Applicant: Professorin Dr. Macarena Marin
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401830362

Ineffective nodules are common in agricultural fields and constitute a limitation to the widespread use of biological nitrogen fixation in agriculture. What makes a nodule effective is the product of multiple factors, from the inherent capacity of rhizobia to fix nitrogen, to their compatibility with the host. How other root associated microbes impact nodule function has not been thoroughly investigated. In the first funding period we have shown that i) although Lotus nodules from different species and soil inoculums are dominated by Rhizobiales bacteria, the diversity and exact composition can vary greatly, ii) nodule composition largely depends on the inoculum, but the host genotype and health status also contribute, iii) L. burttii is more promiscuous than other Lotus plants, which can lead to the formation of ineffective nodules, iv) healthy L. burttii nodules are enriched in Pseudomonas, and v) co-isolated nodule endophytes promote growth in a host specific manner. In the second funding period we aim to elucidate how nodule endophytes impact nodule function through interactions with rhizobia and the host. To investigate this, we will apply a reductionist approach based on the reconstruction of synthetic microbial communities in gnotobiotic systems. In an interdisciplinary study including microbiology, computational biology and genetics we will i) identify and characterise nodule endophytes promoting formation of effective nodules and ii) find the genetic determinants underlaying host specific growth promotion by nodule endophytes. This interdisciplinary and collaborative project will help us understand the formation of effective nodules so in the future we can improve agricultural practices to avoid the establishment of ineffective root nodule symbioses.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2125: Deconstruction and Reconstruction of the Plant Microbiota "DECRyPT"
• International Connection: Switzerland