Drought-mitigating Pseudomonas putida Strain Modulates Polyamine Catabolism in Arabidopsis thaliana

Plant growth-promoting rhizobacteria often play a significant role in alleviating drought stress in plants by colonizing the rhizosphere through myriad mechanisms. We have previously reported that the drought-mitigating rhizobacterium, Pseudomonas putida GAP-P45, modulates polyamine biosynthetic gene expression and cellular accumulation of polyamines (putrescine, spermidine, and spermine) in water-stressed Arabidopsis thaliana (Sen et al. in Plant Physiol Biochem 129:180-188, 2018). In continuation, here, we report the effect of the aforementioned strain on the expression of polyamine catabolic genes (CuAO1-3, PAO1-5), activities of catabolic enzymes (copper amine oxidase and polyamine oxidase), and accumulation of catabolic by-product, gamma-amino butyric acid (GABA) in water-stressed A. thaliana. Similar to the previously reported increase in polyamine biosynthesis and accumulation, P. putida GAP-P45 inoculation under water stress led to significant upregulation of most polyamine catabolic genes at most time points of study. GAP-P45 inoculation of water-stressed A. thaliana increased mostly copper amine oxidase activity in the plants, while polyamine oxidase activity showed either similar or slightly increased levels as compared to the non-inoculated, water-stressed seedlings. The accumulation of GABA in A. thaliana was differentially impacted under these conditions. We conclude that P. putida GAP-P45 tightly regulates polyamine metabolism at least at the transcriptional level under water stress. Taken together with our previous study, the data obtained from the current study point towards GAP-P45 mediated enhanced putrescine turnover and a possible feedback inhibition of polyamine back-conversion due to net accumulation of free putrescine in A. thaliana under water stress.

Automated summary

The study reveals that the plant growth-promoting rhizobacterium Pseudomonas putida GAP-P45 tightly regulates polyamine metabolism in water-stressed Arabidopsis thaliana, impacting both biosynthesis and catabolism of polyamines. The inoculation of GAP-P45 led to the upregulation of polyamine catabolic genes and increased activity of copper amine oxidase, indicating enhanced putrescine turnover in water-stressed plants. Additionally, the accumulation of GABA was differentially impacted under these conditions, suggesting a complex interplay of polyamine metabolism under water stress.