Nitrogen is essential for plant growth. Plants cannot directly assimilate the abundant nitrogen gas available in our atmosphere; instead, they rely on the uptake of inorganic forms of nitrogen. Approximately, half of the N fertilizer used in agriculture is lost through volatilization into the atmosphere, increasing the N 2 O concentrations in the atmosphere, contributing to greenhouse gas emissions and global warming. N fertilizers also leach from the soil profile to underground water systems, contributing to the eutrophication of water bodies. Nitrate contamination of public water resources has significantly increased with the use of N fertilizers and may pose serious health challenges to the general population. There is a growing need to develop sustainable alternative agricultural practices that reduce the extensive use of inorganic nitrogen fertilizers and improving Biological Nitrogen Fixation (BNF) in cereal crops is a long-sought objective, however no successful modification of cereal crops showing increased BNF has been reported. Here, we described a novel approach in which rice and wheat plants were genetically modified to increase the production of compounds that stimulated biofilm formation in soil diazotrophic bacteria, improving BNF with increased grain yield at limiting soil nitrogen contents. We first used a chemical screening to identify plant-produced compounds that induced biofilm formation in nitrogen-fixing bacteria and demonstrated that some flavones induced BNF. We then used CRISPR-based gene editing targeting pathways for flavones breakdown in cereals, increasing the flavone plant contents and root exudation. When grown at limiting soil nitrogen conditions, modified rice plants displayed increased grain yield. Biofilm production also modified the root microbiome structure, favoring the enrichment of diazotrophic bacteria recruitment. Our results support the manipulation of plant biosynthetic pathways as a feasible strategy for the induction of biological nitrogen fixation in cereals and a reduction in the use of inorganic nitrogen fertilizers.
Eduardo Blumwald — Blumwald's research program is multidisciplinary in nature, combining physiology, biochemistry, molecular biology, genomics and proteomics. The general objectives of his work are: (i) the cellular and molecular mechanisms that regulate ion homeostasis in plants; (ii) the cellular and molecular mechanisms mediating the response(s) of plants to abiotic stress (salt, drought, heat, etc.); (iii) the biochemical and molecular basis of sugar and acid accumulation in citrus fruits; and (iv) the development of genomic and proteomic resources for the improvement of fruit quality.