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

• Arabidopsis polyamine uptake transporter 2 ( At PUT2) is required for systemic acquired resistance (SAR). • Putrescine transport is key for polyamine-mediated systemic immune responses. • At PUT2 is essential for putrescine-systemic induction of ICS1 and FMO1 genes. • At PUT2-mediated putrescine transport regulates systemic salicylic acid and ROS levels. • put2-1 mutant exhibited attenuated responsiveness to stomata closure induced by flg22 • The proper timing of SA, ROS, and polyamine accumulation is crucial for SAR establishment. The study of polyamine transport in plants has become increasingly important due to the central role of these amines in regulating growth, development, adaptation, and stress responses. This research focused on the Arabidopsis thaliana Polyamine Uptake Transporters gene family under conditions of systemic acquired resistance. We evaluated all single mutants of this gene family and found that the put2-1 mutant abolished systemic acquired resistance while enhancing basal resistance to Pseudomonas syringae pv. tomato DC3000. In contrast, the 35S::PUT2 overexpression lines showed improved resistance and reduced bacterial titers compared to wild-type plants. RNA-seq analysis revealed that the put2-1 mutant had deregulated expression of genes involved in the biosynthesis, signaling, and inactivation of salicylic acid and N-hydroxypipecolic acid. Most of these genes were transcriptionally upregulated by putrescine in wild-type plants, but not in the put2-1 mutant. Putrescine supplementation increased endogenous putrescine and salicylic acid levels in wild-type plants but not in put2-1 , highlighting the essential role of this transporter in facilitating putrescine mobilization and regulating salicylic acid in distal tissues. We found that the defective systemic acquired resistance phenotype in the put2-1 mutant was linked to changes in the timing of polyamines, ROS, phenolic compound accumulation, and alterations in stomatal immunity. Our study emphasizes the key role of the Polyamine Uptake Transporter 2 (PUT2/LAT4) in establishing systemic acquired resistance in Arabidopsis , while also maintaining the plant’s intrinsic basal resistance mechanisms. These findings offer valuable insights into the complex mechanisms of plant resistance, positioning polyamine transport as a central hub in systemic responses.