How legumes create an environment for nitrogen fixation: control of oxygen permeation into nodules

• Applicant: Professorin Dr. Macarena Marin
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 325528135

Legumes host symbiotic rhizobia inside root structures called nodules where they create an environment suitable for nitrogen fixation. Understanding how this environment emerges is critical for optimizing this symbiosis in legumes and engineering nodulation in other crops. In the first funding period we explored the natural diversity of the symbiotic phenotypes of Lotus using comparative transcriptomics. Thereby we identified genes that were specifically upregulated in infected nodules and thus might mediate the accommodation of rhizobia inside these structures. Phylogenetic and expression analysis of two nodule induced suberin biosynthesis genes encoding Fatty acyl-CoA reductases (FARs) revealed diversification in their expression pattern. Spatiotemporal analysis of promoter activity controlling the expression of these and other suberin-related genes showed distinct activation in the root and nodule endodermis. Mutant lines in the nodule specific FAR3.2 gene, showed an increase in nodule permeability, impaired nitrogen fixation, and reduced shoot growth. Our results support a model in which nodule-specific suberin related genes mediate the formation of a permeation barrier in the nodule periphery. The control of oxygen permeation into the nodule is essential to protect the oxygen-sensitive nitrogenase and is thus crucial for nitrogen fixation. In this project we will investigate the function and regulation of genes with suberin-related functions, as they are promising molecular markers for the establishment of the nodule barrier, which controls oxygen permeation. To this end we will create mutant lines by CRISPR/Cpf1 gene editing and phenotypically characterize them, we will generate reporter lines to determine the ontogeny of the nodule barrier, and will investigate the regulation of suberin-related genes at a molecular level. This work will advance our understanding of how the nodule barrier is formed, a key adaptation enabling nitrogen fixation in legumes.

• DFG Programme: Research Grants
• International Connection: Switzerland