In oat production, the over-application of nitrogen (N) fertilizer in fields due to low N fertilizer use efficiency not only increases production costs but also causes environmental pollution. Currently, mining low N-tolerant oat varieties is an important way to promote sustainable agriculture. In this study, 30 oat varieties were grown in a seedling culture with two treatments of normal N (10 mM NH₄NO₃) and low N (1.25 mM NH₄NO₃), and the correlations between agronomic traits and plant N content and low N tolerance coefficients and indices were determined, which can be used as indicators for the evaluation of low N-tolerant oat varieties. Coefficient of variation, correlation analysis, principal component analysis, partial least-squares discrimination analysis, random forest analysis, least absolute shrinkage and selection operator regression and model evaluation, and membership function analysis were used for in-depth analysis of these indicators. Plant N content, root–crown ratio, and dry weight of aboveground plant parts were found to be important indicators of low N tolerance in oats. According to the membership function ranking of the 30 selected oat varieties, Jiayan 2, Qingyongjiu 035, and Qingyin 2 had strong tolerance to low N stress and Qingyongjiu 003, Qingyongjiu 021, and Qingyongjiu 016 had poor tolerance to low N stress. Thus, this study provides a reliable and comprehensive method for evaluating the low N tolerance of oat varieties as well as a reference for screening other low N-tolerant plants.

The GRAS protein family is involved in plant growth and development, plant disease resistance, and abiotic stress response. Although the GRAS protein family has been systematically studied and reported in many plants, it has not been reported in oat, an excellent foodstuff crop of Gramineae. We identified 90 AsGRAS genes and all of the AsGRAS genes were randomly distributed on 21 chromosomes with 6 tandem duplicated genes and 49 pairs of segmental duplications, which may be the main reason for the expansion of the GRAS gene family. According to the phylogenetic tree, 90 AsGRASs were classified into 10 distinct subfamilies. Gene structure revealed introns varying from zero to seven, and all genes have conserved motifs and GRAS structure domain. Protein–protein interaction and miRNA prediction analysis showed that AsGRAS proteins mainly interacted with GA signalling, cell division, etc., and that the AsGRAS genes were targeted by miRNA171. RNA-seq and qRT–PCR data showed that GRAS genes were expressed at different growth and developmental stages and under different abiotic stresses in oat, indicating the potential role of GRAS genes in promoting growth and stress tolerance in oat. Overall, our evolutionary and expression analysis of AsGRAS genes contributes to the elucidation of a theoretical basis for the GRAS gene family. Moreover, it helped reveal gene function and laid the foundation for future agricultural improvement of oats based on functional properties.

Background: Oat (Avena sativa L.) is a vital forage and cereal crop widely cultivated on the Qinghai–Tibet Plateau, known for its outstanding adaptability to barren soils. Nitrogen (N) is a critical macronutrient, and the excessive application of N fertilizers has triggered severe ecological crises. Identifying key genes regulating adaptation to low N stress is essential for breeding N-efficient oat varieties. The DNA-binding with one finger (Dof) transcription factors play crucial roles in plant stress responses, but their precise molecular mechanisms in oat N-deficiency adaptation remain largely unknown. Results: In this study, we conducted a comprehensive genome-wide identification and unveiled 54 AsDof genes in the oat genome. Phylogenetic, synteny, and promoter analyses revealed their high evolutionary conservation and complex potential roles in stress networks. Transcriptome profiling under low N stress pinpointed AsDof6.5 as a potential candidate. Ectopic expression of AsDof6.5 in Arabidopsis thaliana significantly enhanced plant adaptation to low N. This was morphologically manifested as enhanced primary root elongation, increased root hair number, and significantly higher fresh weight under N-deprived conditions. Physiological assays further demonstrated that AsDof6.5 overexpression efficiently reduced malondialdehyde (MDA) accumulation while simultaneously preserving soluble protein (SP) levels. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays demonstrated that AsDof6.5 has the potential to physically interact with the transcription factor AsWRKY3 and the cytokinin dehydrogenase AsCKX2 in the nucleus. Furthermore, AsDof6.5 overexpression caused a significant transcriptional suppression of downstream CKX2 homologs, which likely serves to fine tune local cytokinin homeostasis, thereby sustaining root developmental plasticity and vitality under severe low N stress. Conclusions: Our findings reveal a novel protein complex transcriptional regulatory hypothetical module. This module effectively enhances adaptation to low N by integrating nutrient starvation signaling with cytokinin homeostasis, providing a theoretical basis and valuable genetic resources for breeding N-efficient crops.