Transcriptome Analysis Reveals Differences in Key Genes and Pathways Regulating Carbon and Nitrogen Metabolism in Cotton Genotypes under N Starvation and Resupply

Nitrogen (N) is the most important limiting factor for cotton production worldwide. Genotype-dependent ability to cope with N shortage has been only partially explored in cotton, and in this context, the comparison of molecular responses of cotton genotypes with different nitrogen use efficiency (NUE) is of particular interest to dissect the key molecular mechanisms underlying NUE. In this study, we employed Illumina RNA-Sequencing to determine the genotypic difference in transcriptome profile using two cotton genotypes differing in NUE (CCRI-69, N-efficient, and XLZ-30, N-inefficient) under N starvation and resupply treatments. The results showed that a large genetic variation existed in differentially expressed genes (DEGs) related to amino acid, carbon, and nitrogen metabolism between CCRI-69 and XLZ-30. Further analysis of metabolic changes in cotton genotypes under N resupply showed that nitrogen metabolism and aromatic amino acid metabolism pathways were mainly enriched in CCRI-69 by regulating carbon metabolism pathways such as starch and sucrose metabolism, glycolysis/gluconeogenesis, and pentose phosphate pathway. Additionally, we performed an expression network analysis of genes related to amino acid, carbon, and nitrogen metabolism. In total, 75 and 33 genes were identified as hub genes in shoots and roots of cotton genotypes, respectively. In summary, the identified hub genes may provide new insights into coordinating carbon and nitrogen metabolism and improving NUE in cotton.