Project description:Rhizobia are soil bacteria that induce nodule formation on leguminous plants. In the nodules, they reduce dinitrogen to ammonium that can be utilized by plants. Besides nitrogen fixation, rhizobia have other symbiotic functions in plants including phosphorus and iron mobilization and protection of the plants against various abiotic stresses including salinity. Worldwide, about 20% of cultivable and 33% of irrigation land is saline, and it is estimated that around 50% of the arable land will be saline by 2050. Salinity inhibits plant growth and development, results in senescence, and ultimately plant death. The purpose of this study was to investigate how rhizobia, isolated from Kenyan soils, relieve common beans from salinity stress. The yield loss of common bean plants, which were either not inoculated or inoculated with the commercial R. tropici rhizobia CIAT899 was reduced by 73% when the plants were exposed to 300 mM NaCl, while only 60% yield loss was observed after inoculation with a novel indigenous isolate from Kenyan soil, named S3. Expression profiles showed that genes involved in the transport of mineral ions (such as K+, Ca2+, Fe3+, PO43-, and NO3-) to the host plant, and for the synthesis and transport of osmotolerance molecules (soluble carbohydrates, amino acids, and nucleotides) are highly expressed in S3 bacteroids during salt stress than in the controls. Furthermore, genes for the synthesis and transport of glutathione and γ-aminobutyric acid were upregulated in salt-stressed and S3-inocculated common bean plants. We conclude that microbial osmolytes, mineral ions, and antioxidant molecules from rhizobia enhance salt tolerance in common beans.
Project description:Common bean (Phaseolus vulgaris L.) is the most consumed grain legume in developing countries in Latin America and Sub-Saharan Africa1. Like other legumes, common bean seeds are rich in protein, carbohydrates, fibers and other health-promoting phenolic compounds thus being vital for food security and income source for local small farmers2. Seed quality traits depend on accumulation of various storage molecules during the seed development (SD) process and influenced by the genotype and adaptive changes to environment3. Concerning common bean, there is still a lack of a deeper molecular knowledge of SD that is hampering the development of new biotech approaches for seed trait modulation and could timely address challenges of agriculture or industry. Our present work aims to unravel the molecular mechanisms underlying SD using a proteomic approach. To achieve this goal, we characterized SD in terms biomass, seed length and weight in the genotype SER16, one of the most promissory drought-resistant release of the CIAT-CGIAR. Seed samples were collected at the 4 main SD stages: Late-Embryogenesis (10 days after anthesis, d.a.a.), Early (20 d.a.a.) and Late Maturation (30 d.a.a.) and Desiccation (40 d.a.a.). The analysis of bean proteome was conducted using a gel-free proteomic analysis (LC-MS/MS) under the scope of EU-FP7-PRIME-XS project. A total of 410 unique proteins were differentially expressed throughout the 4 major seed development stages, in which most of the identified proteins belong in the ‘protein metabolism’ (31,98%) functional category, that includes synthesis, regulation, folding. Other functional categories are represented such as carbohydrate and lipid metabolism (11,26%) and stress/defense and redox metabolism (11,04%). We identified 93 proteins were unique to the first (10-20 d.a.a.), 22 to the second (20-30 d.a.a.) and 40 to the last (30-40 d.a.a.) phase transition, reflecting the major biological processes occurring at this specific seed developmental stage. This study will contribute to reveal key metabolic pathways and mechanisms with potential role in modulating common bean seed development and quality traits.