Nitrogen Fertilization Modulates Soybean Nodulation and Nitrogen Fixation via NO-Mediated S‑Nitrosylation

Soybean, a symbiotic nitrogen-fixing
crop, experiences
suppressed
nodule nitrogen fixation under excessive nitrogen fertilizer. Nitric
oxide (NO) is a key signaling molecule regulating development and
stress, primarily via protein S-nitrosylation, although its role in
soybeans is unclear. Using a unilateral nodulation system, treatments
with nitrogen, an NO scavenger, and an NO donor were applied. Results
showed that nitrogen application increased the NO content in the nodules
and reduced the nitrogen fixation capacity. Conversely, the NO scavenger
lowered the NO levels but enhanced fixation. Exogenous NO inhibited
fixation by damaging the nodule structure, reducing leghemoglobin,
and disrupting NO homeostasis. Quantitative proteomics with iodoTMT
labeling identified 287 S-nitrosylation sites on 238 nodule proteins.
Nitrogen-altered proteins were involved in nitrogenase activity, stress
response, and ABC transporters. This study establishes the ’nitrogen
level-NO signal-S-nitrosylation-nodule function’ pathway, offering
molecular insights into S-nitrosylation’s role in nodule regulation.