Role of flavins in the resistance of Sinorhizobium meliloti – alfalfa association to Aphanomyces root rot

Priority area:

Novel approaches to disease and fertility management that transcend traditional organic approaches and seek to exploit and integrate biological and chemical processes.

Flavins (riboflavin, FMN and FAD; vitamin B2) are bioactive molecules that have a beneficial effect on plant growth and soil quality. Recently we found that mutations in the riboflavin biosynthetic pathway affect the abundant flavin secretion by the nitrogen-fixing plant symbiont Sinorhizobium meliloti. We also have found that flavins play a critical role in the ability of S. meliloti to promote plant-host adaptation to environmental stresses – the features defining the efficiency of bacterial inoculums used as a part of Rhizobium-Legume crop system. However, the impact of rhizobia on the ability of the associated alfalfa to resist a pathogen attack or the effect of disease on symbiotic performance has not been evaluated. The goal of this research is to test the interaction of S. meliloti and Aphanomyces euteiches root rot on alfalfa. We speculate that the rhizobia will affect resistance/susceptibility of alfalfa and will evaluate the role of bacteria produced flavins on alfalfa resistance to the pathogen.


Grant Information

  • Project ID: 126
  • Project Status: Complete


  • Principal Investigator(s): Yurgel, S.
  • Grant Amount: $39,000



Sinorhizobium meliloti flavin secretion and bacteria-host interaction: role of the bifunctional RibBA protein. Yurgel SN, Rice J, Domreis E, Lynch J, Sa N, Qamar Z, Rajamani S, Gao M, Roje S, Bauer WD. Mol Plant Microbe Interact. 2014 May; 27(5):437-45.

Protocols published:

Assay for GTP cyclohydrolase II activity in bacterial extracts. Yurgel SN, Sa N, Rice J and Roje. 2014.

Quantification of flavin production by bacteria. Yurgel SN, Lynch J, Rice, Adhikari N, Roje S. 2014.

Abstract/Poster: Sinorhizobium meliloti flavin secretion and bacteria-host interaction: role of the bifunctional RibBA protein. Yurgel SN, Rice J, Lynch J, Sa N, Roje S, Bauer WD. Plant Biology 2014. Annual scientific meeting of the American Society of Plant Biologists, July 12-16, 2014, Portland.

Additional Funds Leveraged

Five applications for alternative sources of competitive non-university funds have been submitted through CAHNRS Office of Research/ARC: (1) Full proposal to USDA AFRI (2013), (2-3) Pre-proposal to NSF (2013 and 2014), and (4-5) R21 proposal (2013) and R01 (2014) to NIH-NIAID.


  • Short-Term: Two assays to study alfalfa/S. meliloti/A. euteiche interaction have been developed. The comparison of these assay showed that the greenhouse experiments are more reliable for detection of the effect of A. euteiche infection on S. meliloti-alfalfa association.  However the sterile growth-chamber experiments could be used to study the effect of S. meliloti inoculation on the development of Aphanomyces root rot.  Our data showed that (i) inoculation with rhizobia could improve the ability of the associated host-plant to resist a pathogen attack and (ii) A. euteiche infection adversely impacts the S. meliloti–alfalfa symbiosis. We did not detect a significant role of bacteria-derived flavins in the improved resistance of rhizobia associated alfalfa plants to A. euteiche infection.  The manuscript describing this research is in preparation.
  • Intermediate-Term:  The data obtained in this research provide a foundation for comprehensive investigation of mechanisms of anti-fungal effect Sinorhizobium symbiosis on Medicago-A. euteiche association and for a search for alfalfa-Sinorhizobium combination with high level of symbiotic nitrogen fixation and improved resistance to fungal infection (see recommendations for future research).
  • Long-Term:  The results obtained in this research could promote the creation of rhizobial inoculums, which provide host-plant with both (i) sufficient nitrogen for growth and (ii) antifungal protection under A. euteiche attack.