Transcriptomic and metabolomic analysis reveals that symbiotic nitrogen fixation enhances drought resistance in common bean.

Common bean (Phaseolus vulgaris L.), one of the most important legume crops, use atmospheric nitrogen through symbiosis with soil rhizobia reducing the nitrogen fertilization needs. However, this legume is particularly sensitive to drought conditions, prevalent in arid regions where this crop is cultured. Therefore, studying the response to drought is important to sustain crop productivity. We have used integrated transcriptomic and metabolomic analysis to understand the molecular responses to water deficit in a marker-class common bean accession cultivated under N2-fixation or fertilized with nitrate (NO3-). RNA-seq revealed more transcriptional changes in the plants fertilized with NO3- than in the N2-fixing plants. However, changes in N2-fixing plants were more associated with drought tolerance than in the NO3- fertilized ones. N2-fixing plants accumulated more ureides in response to drought and GC/MS and LC/MS analysis of primary and secondary metabolites profiles revealed that N2-fixing plants also had higher levels of ABA, proline, raffinose, amino acids, sphingolipids and triacylglycerols than the NO3- fertilized ones. Moreover, plants grown under nitrogen fixation recovered from drought better than plants fertilized with NO3-. Altogether we show that common bean plants grown under symbiotic nitrogen fixation were more protected against drought than the plants fertilized with nitrate.