Melatonin promotes nodule development enhancing soybean nitrogen metabolism under low nitrogen levels

Nitrogen availability profoundly impacts crop productivity, especially for soybeans, which exhibit a substantial demand for nitrogen. In response to the over-reliance on nitrogen fertilizers, which poses both inefficiencies and environmental concerns, the potential of melatonin in enhancing nitrogen uptake and utilization in soybeans through root irrigation was investigated. Melatonin significantly increased the activity of ammonium assimilating enzymes, thereby enhancing plant tolerance to low nitrogen levels, particularly at a concentration of 10 μM. This phenomenon has been conclusively linked to the augmented nitrogen fixation and utilization capacity, attributed to the facilitating rhizobial infection. Notably, melatonin influenced flavonoid content, specifically inducing genistein levels, essential for rhizobial infection. The malonyltransferase-encoding gene GmMaT2, which modifies isoflavones, was found to be crucial for the effects of melatonin on nodulation and nitrogen metabolism. The silence of GmMaT2 hindered the beneficial effects of melatonin on nodule development and attenuated its ability to enhance aspects of low nitrogen tolerance in soybean. It was elucidated that the potential of melatonin as a sustainable strategy for enhancing nitrogen utilization efficiency in soybeans. It provided insights into the underlying mechanisms and underscored the significance of GmMaT2 in mediating the beneficial effects induced by melatonin under low nitrogen conditions. The findings present a promising solution for mitigating agricultural costs and environmental impacts.