How to catch the N – An inter‐species exchange with the right chemistry

Abstract

While classical breeding traits have focussed on above-ground tissues, it is becoming clear that underground aspects of plant life are a hidden treasure of tools applicable for resilient crop production. Plants of the legume family develop specialized organs, called nodules, which serve as hosts for Rhizobium bacteroids. A highly specialized symbiotic relationship exists deep inside the nodules. In exchange for carbohydrates, host-specific rhizobia bacteroids can assimilate nitro- gen from the air and fix it into a form that can be used by plants in a process known as biological nitrogen fixation. While we understand certain aspects of how this inter-species relationship is established, the exact biochemistry of this exchange remains dogmatic. In their recent work, Christen and colleagues (Flores-Tinoco et al, 2020) challenge the current model of nitrogen exchange and argue that that an expanded model is needed to fit experi- mental findings related to nitrogen fixa- tion. The authors perform an elegant set of experiments and highlight that rather than a single-way flow of nitrogen, the N-fixing process is in fact an elaborate metabolic exchange between the nodule- dwelling bacteroids and the host plant. Importantly, this work provides an updated theoretical framework with the “catchy” name CATCH-N which delivers up to 25% higher yields of nitrogen than clas- sical models and is suitable for rational bioengineering and optimization of nitro- gen fixation in microorganisms.