Diversification of cytokinin phosphotransfer signaling genes in Medicago truncatula and other legume genomes

• Published in: BMC genomics 2019-05, Vol.20 (1), p.373-373, Article 373
• Main Authors: Tan, Sovanna, Debellé, Frédéric, Gamas, Pascal, Frugier, Florian, Brault, Mathias
• Format: Article
• Language: English
• Subjects: Alfalfa; Amino acids; Arabidopsis; Arabidopsis thaliana; Asparagine; Aspartate; Bacteria; Brain; Cell division; Chickpeas; Cytokinin signaling; Cytokinins; Cytoplasm; Deoxyribonucleic acid; DNA; DNA binding proteins; Gene expression; Genes; Genetic aspects; Genomes; Genomics; Gibberellins; Glutamate; Glycine; Glycine max; Grapes; Growth; Histidine; Histidine kinase; Kinases; Legumes; Life Sciences; Medicago truncatula; Negative feedback; Nitrogen fixation; Nodulation; Nodules; Organs; Phaseolus vulgaris; Phosphorelay; Phosphors; Phylogenetics; Phylogeny; Pigeonpeas; Plant hormones; Properties; Protein binding; Proteins; Receptors; Regulators; Response regulator; Root nodules; Signal transduction; Signaling; Signaling peptides and proteins; Soils; Soybeans; Symbiotic nitrogen-fixing nodulation; Transcription (Genetics); Transcription factors; Vegetal Biology
• ISSN: 1471-2164; 1471-2164
• DOI: 10.1186/s12864-019-5724-z

Legumes can establish on nitrogen-deprived soils a symbiotic interaction with Rhizobia bacteria, leading to the formation of nitrogen-fixing root nodules. Cytokinin phytohormones are critical for triggering root cortical cell divisions at the onset of nodule initiation. Cytokinin signaling is based on a Two-Component System (TCS) phosphorelay cascade, involving successively Cytokinin-binding Histidine Kinase receptors, phosphorelay proteins shuttling between the cytoplasm and the nucleus, and Type-B Response Regulator (RRB) transcription factors activating the expression of cytokinin primary response genes. Among those, Type-A Response Regulators (RRA) exert a negative feedback on the TCS signaling. To determine whether the legume plant nodulation capacity is linked to specific features of TCS proteins, a genome-wide identification was performed in six legume genomes (Cajanus cajan, pigeonpea; Cicer arietinum, chickpea; Glycine max, soybean; Phaseolus vulgaris, common bean; Lotus japonicus; Medicago truncatula). The diversity of legume TCS proteins was compared to the one found in two non-nodulating species, Arabidopsis thaliana and Vitis vinifera, which are references for functional analyses of TCS components and phylogenetic analyses, respectively. A striking expansion of non-canonical RRBs was identified, notably leading to the emergence of proteins where the conserved phosphor-accepting aspartate residue is replaced by a glutamate or an asparagine. M. truncatula genome-wide expression datasets additionally revealed that only a limited subset of cytokinin-related TCS genes is highly expressed in different organs, namely MtCHK1/MtCRE1, MtHPT1, and MtRRB3, suggesting that this "core" module potentially acts in most plant organs including nodules. Further functional analyses are required to determine the relevance of these numerous non-canonical TCS RRBs in symbiotic nodulation, as well as of canonical MtHPT1 and MtRRB3 core signaling elements.