AUXIN SIGNALING IN ARABIDOPSIS THALIANA EXPOSED TO MICROBACTERIUM SP.

BURGOS HERRERA, GONZALO; CURATTI LEONARDO; DO NASCIMENTO, MAURO; PAGNUSSAT, L.A.

Congreso; SAMIGE 2022; 2022

We showed previously that inoculation with the bacterium Microbaterium sp. exerted a dose-dependent effect on Arabidopsis thaliana seedlings, from growth promotion at low doses to strong inhibition at higher doses. The bacterium produces the effect by producing diffusible volatile and non-volatile substances. In the presence of the bacterium, A. thaliana seedlings displayed a dose-dependent more branched root-architecture and a significant increase in the number of root hairs, suggesting the bacterium might activate auxin signaling in the seedlings.In this report we investigated further this working hypothesis by means of inoculating A. thaliana mutant varieties. Using a transgenic line expressing the reporter gene GUS under the control of an auxin-responsive promoter (DR5-GUS), indicated that diffusible substances produced by the bacterium altered the cell specific pattern of DR5-GUS activation, producing patches of expression in regions beyond the root elongation zone, where DR5-GUS is not express in the absence of the bacterium. The bacterium also altered the characteristic expression of DR5-GUS at the root tips by making it more circumscribed to the root tips, producing noticeable more intense signals, and labeling in an increased number of cells, apparently from which lateral roots would develop. In other experiments, the bacterium also promoted growth of the auxin-insensitive A. thaliana triple mutant line tir1-1afb2,3 at a similar level that that of the wt seedlings. Taking together, these results suggest that although both, volatile and non-volatile substances alter auxin signaling in the seedlings, it appears that auxin signaling is not the more prominent mechanisms of A. thaliana growth promotion by Microbacterium sp. We are currently conducting a proteomic analysis to continue unraveling the mechanism underlying growth promotion and inhibition of this plant-microbe interaction at the molecular level.