About this Research Topic
This Research Topic aims to address the development of new molecular tools to boost research progresses in the field that studies nitrogen fixation during the symbiotic interaction between legume species and bacteria of the Rhizobium genus (Rhizobia). A focus is put on genome editing technologies that allow to create mutants in various legumes species.
The ca. 19,000 known legume species (Leguminosae, commonly known as the pea, or bean family) are a large family of flowering plants. Some species are important agricultural and food plants, such as soybean, bean, pea, chickpea, alfalfa, and peanut. Many legumes can host bacteria within structures called root nodules. These bacteria, known as rhizobia, convert nitrogen gas (N2) into ammonia, which is then assimilated into amino acids, nucleotides, and other plant cellular constituents. In return, plant hosts supply carbohydrates and other nutrients to the bacteria to sustain the biological nitrogen fixation. Legumes are convenient species in agriculture as they require very few nitrogen fertilizer and can be used in a crop rotation to replenish soil that has been depleted of organic nitrogen.
The rhizobia and their hosts recognize each other for nodule initiation and organogenesis. During the last two decades, dozens of genes involved in the nodulation process have been identified. Among those were genes coding nodulation factor receptors, nuclear cation channels, calcium-dependent and calmodulin-dependent protein kinases, transcription factors, and proteins involved in hormone pathways. However, our understanding of the molecular mechanisms of nodule formation and of the maintenance of the nitrogen fixation activity within nodules is still limited. This is largely due to the limited number of available mutants and to the lack of sophisticated tools for detailed analyses of nodulation process at cellular and molecular levels.
This Research Topic welcomes articles focusing on the molecular mechanisms of the legume-rhizobia interactions and on development of appropriate tools to boost research progress in this field. We particularly welcome manuscripts aimed at developing:
- targeted gene knockout technologies (e.g., CRISPR/Cas9) in model legumes species such as Glycine max, Medicago truncatula, and Lotus japonicas, as well as in corresponding rhizobia species
- new methods for creating mutant library in legumes or rhizobia and high throughput screening of their interactions
- omics tools for large scale analyses of dynamic changes of epigenome, RNAs (mRNA, small RNA, lncRNA, etc), proteins, and metabolites in nodules
- biochemical tools for the separation of microcompartments within nodules (e.g. symbiosome membrane, peribacteroid space) and for the quantification or in vivo real-time monitoring of key molecules and biomarkers associated with nodule organogenesis or functioning (e.g. calcium spiking, pH, oxygen, carbon dioxide, nitric oxide, reactive oxygen/nitrogen species)
- bioinformatic tools to assess the complex traits involved in legume-rhizobia symbiosis (e.g. transcriptomics/proteomics/metabolomics analytical methods, CRISPR-Cas9 guide RNA design and gRNA library construction, genome-wide association studies)
- mathematical modelling of the determinate or indeterminate nodules development, distribution of essential hormones (e.g. auxin, cytokinin) and simulation the physiological responses.
Keywords: CRISPR-Cas9, legume, rhizobia, symbiosis, nitrogen fixation
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