Polyamine uptake transporter 2 is essential for systemic acquired resistance establishment in Arabidopsis.

Plants have evolved a tightly regulated and inducible immune system to resist pathogen attack. After the initial contact with the pathogen, plants are significantly more resistant to future challenges, even from unrelated pathogens, an event known as systemic acquired resistance (SAR). In plants polyamines are involved in the regulation and establishment of the defense response by modulating their metabolism, specifically their biosynthesis, conjugation and catabolism. However, it is not known whether polyamine transport is involved in the plant defense response. Herein, we demonstrate that the PUT2/LAT4 transporter is required to establish local immunity and systemic defense responses in the A. thaliana-Pseudomonas syringae pv. tomato DC3000 (Pst) pathosystem. Our data revealed a dual phenotype in the put2-1 mutant after Pst inoculation, on one side, SAR was abolished in the systemic leaves while on the other, basal resistance to Pst was enhanced. Remarkably, this phenotype persisted even upon inoculation with unrelated pathogens such as Botrytis cinerea, highlighting a broad-spectrum SAR deficiency. To gain deeper insights into the involvement of PA transport in SAR, transcriptomic and metabolomic data of the put2-1 mutant were obtained. To investigate the participation of the polyamine uptake transporter 2 (PUT2) gene in SAR, we used six-week-old plants and selected the lower leaves [8, 9 and 10; for mock or local priming with Pseudomonas syringae pv. tomato DC30000 (Pst)] and collected the upper leaves of Arabidopsis thaliana rosette (13, 14, and 15; non-inoculated or systemically challenged with Pst). Therefore four conditions were established: native plant status (a), local priming (b), systemic challenge (c), and both local priming and systemic challenge (d). Three biological replicates were submitted for standard mRNA sequencing. We then performed gene expression profiling analysis of RNAseq data from the WT and the put2-1 mutant line under native or SAR conditions. Samples of the native plant status (a) and local priming (b) were obtained from the upper leaves, 24 h after mock or Pst inoculation of the lower leaves. Sampleas of the systemic challenge (c), and both local priming and systemic challenge (d), were obtained from the upper leaves 24 h after inoculation of the upper leaves with Pst. This second inoculation was performed 48 h after the first inoculation in local leaves. Comparative gene expression analysis of SAR vs. native conditions between WT and the put2-1 mutant were performed.