Transcriptome Differences in Response Mechanisms to Low-Nitrogen Stress in Two Wheat Varieties

Nitrogen plays a crucial role in wheat growth and development. Here, we analyzed the tolerance of wheat strains XM26 and LM23 to low-nitrogen stress using a chlorate sensitivity experiment. Subsequently, we performed transcriptome analyses of both varieties exposed to low-nitrogen (LN) and normal (CK) treatments. Compared with those under CK treatment, 3534 differentially expressed genes (DEGs) were detected in XM26 in roots and shoots under LN treatment (p < 0.05, and |log2FC| > 1). A total of 3584 DEGs were detected in LM23. A total of 3306 DEGs, including 863 DEGs in roots and 2443 DEGs in shoots, were specifically expressed in XM26 or showed huge differences between XM26 and LM23 (log2FC ratio > 3). These were selected for gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. The calcium-mediated plant–pathogen interaction, MAPK signaling, and phosphatidylinositol signaling pathways were enriched in XM26 but not in LM23. We also verified the expression of important genes involved in these pathways in the two varieties using qRT-PCR. A total of 156 transcription factors were identified among the DEGs, and their expression patterns were different between the two varieties. Our findings suggest that calcium-related pathways play different roles in the two varieties, eliciting different tolerances to low-nitrogen stress.

Unravelling the genetic architecture of grain quality traits under optimum and low-nitrogen stress conditions using tropical maize (Zea mays L.) germplasm

Soils in sub-Saharan Africa are nitrogen deficient due to low fertilizer use and inadequate soil fertility management practices. This has resulted in a significant yield gap for the major staple crop maize, which is undermining nutritional security and livelihood sustainability across the region. Dissecting the genetic basis of grain protein, starch and oil content under nitrogen-starved soils can increase our understanding of the governing genetic systems and improve the efficacy of future breeding schemes. An association mapping panel of 410 inbred lines and four bi-parental populations were evaluated in field trials in Kenya and South Africa under optimum and low nitrogen conditions and genotyped with 259,798 SNP markers. Genetic correlations demonstrated that these populations may be utilized to select higher performing lines under low nitrogen stress. Furthermore, genotypic, environmental and GxE variations in nitrogen-starved soils were found to be significant for oil content. Broad sense heritabilities ranged from moderate (0.18) to high (0.86). Under low nitrogen stress, GWAS identified 42 SNPs linked to grain quality traits. These significant SNPs were associated with 51 putative candidate genes. Linkage mapping identified multiple QTLs for the grain quality traits. Under low nitrogen conditions, average prediction accuracies across the studied genotypes were higher for oil content (0.78) and lower for grain yield (0.08). Our findings indicate that grain quality traits are polygenic and that using genomic selection in maize breeding can improve genetic gain. Furthermore, the identified genomic regions and SNP markers can be utilized for selection to improve maize grain quality traits.

Glucose-6-Phosphate Dehydrogenase Is Involved in the Tolerance of Soybean Seedlings to Low Nitrogen Stress

Nitrogen (N) deficiency affects plant growth and crop yield. In this study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in response to N availability in three soybean cultivars, JINDOU 19 (JD19), LONGHUANG 3 (LH3), and LONGDOU 2 (LD2), that have different tolerances to low-N stress. The results showed that the leaf area and primary root length of JD19 and LH3 were greater than that of LD2 under low-N stress, suggesting that the growth of JD19 and LH3 were impaired less than LD2, and thus are more tolerant to low-N stress than LD2 is. Interestingly, the G6PDH expression showed different degrees of change in these soybean cultivars under low-N conditions, and the G6PDH activity in JD19 and LH3 was higher than that in LD2. When G6PDH was inhibited by glucosamine (GlcN), the contents of malondialdehyde (MDA) and H2O2 were dramatically increased under low-N stress. Meanwhile, the activities of N metabolism-related enzymes were inhibited. These results indicate that G6PDH is involved in the tolerance of soybean cultivars to low-N stress through affecting the N metabolism. Furthermore, under low-N conditions, the contents of NADP+ and reduced glutathione (GSH) in JD19 and LH3 were increased more than that in LD2. In contrast, the activity of the plasma membrane (PM), NADPH oxidase, and the NADPH content in JD19 and LH3 were lower than that in LD2. In conclusion, G6PDH reduces the accumulation of ROS in plant cells by modulating NADPH/NADP+ and GSH levels to maintain the growth of soybeans under low-N conditions.