A rapid visual detection system for nitrogen-fixation activity in soybean root nodules

Nitrogenase plays a critical role in biological nitrogen fixation. However, current methods for detecting nitrogenase activity are labor-intensive and unsuitable for large-scale applications. To address this issue, we developed a real-time visual detection system for nitrogen-fixation ability in soybean ( Glycine max ) nodules using reporter gene-tagged rhizobial strains. Among the four reporters tested, the LUX reporter gene provided the most promising results for deep-tissue imaging because, unlike GFP and RFP, it suffers no autofluorescence interference, and unlike GUS, it does not require exogenous substrate. Further screening identified the nitrogenase-correlative promoter pc16350, which drove LUX expression with high sensitivity at levels strongly correlated to nitrogenase activity. This system enables the rapid, non-invasive monitoring of nitrogen-fixation activity in soybean nodules.