Integrated Transcriptomic and Metabolomic Analyses Reveal Leaf Regulatory Mechanisms Underlying Low-Nitrogen Tolerance in Oat (Avena sativa L.)

Nitrogen deficiency limits oat growth and productivity, but the molecular basis of contrasting low-nitrogen responses among oat germplasms remains poorly understood. This study compared the low-nitrogen-tolerant germplasm Jiayan No.2 with the low-nitrogen-sensitive germplasm ZNY256 after 15 days of hydroponic cultivation under normal nitrogen (10 mM NH4NO3) or low nitrogen (1.25 mM NH4NO3). Growth traits, plant nitrogen content, nitrogen-metabolism-related enzyme activities, soluble sugar content, transcriptomes, and untargeted metabolomes were analyzed. Low nitrogen reduced plant height and plant nitrogen content in both germplasms, with more pronounced changes in ZNY256. Root length was unaffected, whereas root dry weight decreased only in ZNY256. ZNY256 also showed a larger transcriptional response than Jiayan No.2. Functional analyses highlighted phenylpropanoid and flavonoid biosynthesis, glutathione and nitrogen metabolism, ribosome biogenesis, and plant MAPK signaling. Metabolomic profiling identified changes in amino acid-, lipid-, secondary metabolite-, and antioxidant-related features. Integrated analysis and qRT-PCR validation further identified candidate genes associated with these responses. These findings characterize transcriptional and metabolic changes associated with the contrasting responses of the two oat germplasms to nitrogen deficiency and provide candidate genes, metabolites, and pathways for further investigation of low-nitrogen adaptation in oat.