Physiological and transcriptomic response of soybean seedling roots to variable nitrate levels

Nitrate is the main nitrogen source for plant growth and development. Increasing evidence indicates that nitrate plays an important role in root growth and development. However, the effects of different concentrations of nitrate on the physiological and transcriptional response of soybean [Glycine max (L.) Merr.] root development at the seedling stage are not well understood. In this study, we found that both high and low concentrations of nitrate inhibited the growth and development of the soybean root system compared with optimal nitrate supply at the seedling stage. Using transcriptome sequencing technology, we identified 1,654, 1,283, and 2,083 significantly differentially expressed genes in soybean root grown under the low nitrate concentration, optimal nitrate concentration, and high nitrate concentration conditions, respectively. These genes were enriched in the Gene Ontology terms of metabolic process, catalytic activity, and membrane. The genes enriched in the pentose and glucuronate interconversions and glutathione metabolism pathways may play important roles during soybean root response to different concentrations of nitrate. In addition, the expression of 18 nitrate transporter genes changed significantly under different nitrate concentrations. Among them, the expression of two GmNPF6.3 genes was upregulated under the NL condition but downregulated under the NH condition, whereas six GmNPF7.3 genes exhibited opposite expression patterns. Taken together, our physiological data can enable a better understanding of the soybean root response under different nitrate concentrations, and the transcriptome data provide a list of candidate genes for further investigation of the mechanisms of root response under different nitrate concentrations.

Automated summary

Nitrate is essential for plant growth, but both high and low concentrations of nitrate inhibit soybean root development compared to optimal levels. Transcriptome analysis revealed differentially expressed genes related to metabolic processes, catalytic activity, and membrane function in response to different nitrate concentrations, providing insights into the molecular mechanisms of root response.