MECHANISMS ASSOCIATED WITH PROLINE METABOLISM AND REDOX BALANCE IN PEANUT MICROSYMBIONTS EXPOSED TO WATER STRESS

VILLA, JUAN FRANCISCO; BECKER, DONALD; CASTRO, STELLA; FURLAN, ANA LAURA; BIANUCCI, ELIANA

Congreso; LVI SAIB Meeting and XV SAMIGE Meeting; 2020

The exposure of microorganisms to adverse environmental conditions can affect the possibility of establishing interaction with plants. Proline, an osmoprotective amino acid and determinant of cellular redox balance, could increase tolerance to drought stress. Thus, proline addition to peanut inoculants would mitigate drought stress in crops. The objective was to elucidate the fundamental mechanisms of protection against water stress mediated by proline in peanut microsymbionts, exploring the participation of its metabolism in the cellular redox balance. To evaluate whether the addition of proline activates the catabolism of the enzyme and the antioxidant system, we used the microsymbionts recommended as peanut inoculants, Bradyrhizobium sp. SEMIA6144 and Bradyrhizobium sp. C-145. Cultures in exponential phase were treated with different proline doses (0 - 50 mM) for 0 - 60 min to determine viability (CFU ml-1), the transcription of genes from proline catabolism (putA) and antioxidants, catalase (cat) and thioredoxins (trx). Next, we analyzed the effect of proline on growth and redox metabolism of microsymbionts exposed to water stress. Proline concentrat viability and priming effect on peanut seeds. The drought stress condition was imposed by Polyethylene glycol (PEG) addition, whose concentration was selected in viability tests. The treatments were: I) control; II) 50 mM proline; III) 30 mM PEG 6000; IV) 30 mM PEG 6000 + 50 mM proline. Bacterial response was determined through viability, proline content, production of a reactive oxygen species (hydrogen peroxide, H2O2), oxidative damage to lipids by thiobarbituric acid reactive substances (TBARs) and specific activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). The results showed that activation of proline degradation, revealed by elevated putA transcript´s levels, was related to up-regulation of transcripts coding for antioxidants (cat and trx). The addition of 50 mM proline increased the viability of PEG-treated Bradyrhizobium sp. C-145, reaching control values. In the presence of water stress, bacterial cells revealed an increase in proline content and SOD and CAT activities, while upon exogenous proline addition they showed basal levels. In PEG-treated Bradyrhizobium sp. SEMIA 6144, the amino acid addition did not modify the decreased viability and elevated H2O2 and specific activities of SOD and CAT. In conclusion, the transcription of genes coding for the bifunctional enzyme of proline catabolism (putA) could be associated with the generation of excess electrons that react with oxygen, activating a redox-dependent transcription factor, and enhancing the antioxidant response of bacterial cells (cat and trx). Besides, the addition of proline to the culture medium had a protective effect on Bradyrhizobium sp. C-145 growth in the presence of stress, which can be associated with the maintenance of redox balance.