Commonly studied in the context of legume-rhizobia symbiosis, biological nitrogen fixation (BNF) is a key component of the nitrogen cycle in nature. Despite its potential in plant breeding and many years of research, information is still lacking as to the regulation of hundreds of genes connected with plant-bacteria interaction, nodulation, and nitrogen fixation. Here, we compared root nodule transcriptomes of red clover (Trifolium pratense L.) genotypes with contrasting nitrogen fixation efficiency, and we found 491 differentially expressed genes (DEGs) between plants with high and low BNF efficiency. The annotation of genes expressed in nodules revealed more than 800 genes not yet experimentally confirmed. Among genes mediating nodule development, four nod-ule-specific cysteine-rich (NCR) peptides were confirmed in the nodule transcriptome. Gene duplication analyses revealed that genes originating from tandem and dispersed duplication are significantly over-represented among DEGs. Weighted correlation network analysis (WGCNA) organized expression profiles of the transcripts into 16 modules linked to the analyzed traits, such as nitrogen fixation efficiency or sample-specific modules. Overall, the results obtained broaden our knowledge about transcriptomic landscapes of red clover's root nodules and shift the phenotypic description of BNF efficiency on the level of gene expression in situ.

• Keywords
• differentially expressed gene, gene duplication, nodule-specific cysteine-rich peptide, transcriptome,
• Publication type
• Journal Article MeSH

Legumes have played an important part in cropping systems since the dawn of agriculture, both as human food and as animal feed. The legume family is arguably one of the most abundantly domesticated crop plant families. Their ability to symbiotically fix nitrogen and improve soil fertility has been rewarded since antiquity and makes them a key protein source. The pea was the original model organism used in Mendel's discovery of the laws of inheritance, making it the foundation of modern plant genetics. This Special Issue provides up-to-date information on legume biology, genetic advances, and the legacy of Mendel.

• Keywords
• genomics, legumes, nitrogen fixation, proteins,
• MeSH
• Heredity MeSH
• History, 19th Century MeSH
• History, Ancient MeSH
• History, Medieval MeSH
• Fabaceae genetics   metabolism   MeSH
• Phenotype MeSH
• Nitrogen Fixation genetics   physiology   MeSH
• Genetic Variation MeSH
• Genomics * MeSH
• Humans MeSH
• Models, Genetic MeSH
• Crops, Agricultural genetics   history   metabolism   MeSH
• Check Tag
• History, 19th Century MeSH
• History, Ancient MeSH
• History, Medieval MeSH
• Humans MeSH
• Publication type
• Historical Article MeSH
• Introductory Journal Article MeSH
• Editorial MeSH