Nitrogen (N) is an essential macronutrient for plant growth. NIN–like protein (NLP) transcription factors play important roles in nitrate signaling and response in plants. However, a comprehensive analysis of the NLP gene family in sorghum is still lacking. In this study, we identified five NLP genes in sorghum, and a high collinearity of NLP was detected in sorghum, rice and maize. N deficiency decreased SbNLP3 and SbNLP4 expression levels in roots, and the expression of SbNLP1 and SbNLP2 declined in roots during nitrate resupply. Subcellular localization analysis revealed that SbNLP1 was mostly detected in nuclei and cytoplasm. Compared with wild–type rice ZH11 plants, SbNLP1 overexpression plants showed improved low nitrogen (LN) tolerance, with longer roots and shoots under LN conditions. Transcriptome analysis between overexpression lines OE1–5 and ZH11 showed that 773 and 967 differentially expressed genes (DEGs) were identified in roots and shoots under LN conditions, respectively. In contrast, 674 and 1283 DEGs were identified in roots and shoots under normal nitrogen (NN) conditions, respectively. Thirty–seven N–related DEGs were identified in roots through GO enrichment under LN conditions, and terms of plant hormone signal transduction, biosynthesis of secondary metabolites and plant–pathogen interaction were identified through KEGG enrichment. WGCNA analysis also revealed plant hormone signal transduction pathways and plant pathogen interaction pathways in OE1–5 under LN conditions. These results provide a basis for N use efficiency (NUE) improvement in sorghum and functional analysis of SbNLPs.

Sorghum is an important raw material for China’s baijiu (liquor) brewing industry, and the tannin content in its grains directly affects the quality and nutritional value of the liquor. Grain color is closely associated with tannin content, yet the genetic mechanism underlying grain color formation remains incompletely understood. In this study, we systematically observed grain development in the yellow-grained sorghum line GW605. The results showed that from 1 to 16 days after flowering (DAF), the grains underwent a rapid growth phase, after which the expansion rate slowed. On 25 DAF, the green color of the grains gradually faded, shifting from white to yellow and continuously deepening, ultimately turning dark yellow. A segregating population was subsequently constructed using GW605 (yellow grain) and 6E16 (white grain) as parents. Bulked segregant analysis (BSA) localized the gene controlling the yellow grain to chromosome 1. Through fine mapping based on recombinant individuals, the gene was narrowed to a 108 kb physical interval containing seven candidate genes. Sequencing and functional annotation of the candidate genes suggested that Yellow Seed 2 (Sobic.001G397900) is the candidate gene associated with yellow grain color difference between the two parental lines. Haplotype analysis of Yellow Seed 2 using resequencing data from 698 sorghum germplasm accessions detected a total of 11 SNP loci, forming four haplotypes, among which Hap1 was the predominant haplotype. Further analysis revealed that the haplotype diversity of Yellow Seed 2 increased considerably during the domestication process from Chinese landraces to Chinese cultivars, suggesting that this gene may have incorporated genetic lineages from foreign germplasm during domestication.

Leaf morphology influences photosynthesis, transpiration, and, ultimately, crop yield. To elucidate the molecular regulatory mechanisms underlying narrow leaves in Sorghum bicolor, we identified key DEGs (differentially expressed genes) influencing leaf morphology. The nal6 (the narrow-leaf mutant6) was obtained through 0.1% EMS (ethyl methane sulfonate) chemical mutagenesis of the WT (BTX623). Compared with the WT leaves, there were significant differences in leaf width and length at the flowering stage. A total of 1520 DEGs between the nal6 and WT were screened at the flowering stage based on the transcriptome analysis of sword leaves. KEGG and GO enrichment analyses revealed that DEGs were significantly enriched in pathways such as plant signal transduction, cytokinin biosynthesis, photosynthetic antenna proteins, and secondary metabolite biosynthesis. Further analysis indicated that four DEGs are involved in regulating auxin signaling transduction, thirteen DEGs are involved in regulating zeatin signal transduction, and two DEGs are involved in regulating zeatin biosynthesis. These genes are differentially expressed in nal6, directly affecting the signaling of auxin and zeatin and the biosynthesis of zeatin. Our findings provide a theoretical foundation for understanding the molecular regulation of narrow leaves and breeding ideal plant types in Sorghum bicolor.