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Significance Statement Although potentiating resilience is foundational to crop improvement, and despite the notion that cell wall (CW) protects against pathogens, the extent of pathogen‐induced CW changes and the CW composition requirements for a successful defense are largely unknown. By investigating the bacteria‐induced impact on the Arabidopsis CW, we found changes exclusively in infected leaves with the remodeling of distinct CW polysaccharides, including arabinogalactan proteins, whose loss is detrimental to defense, highlighting specific requirements for antagonizing pathogens and potentiating plant defenses. 

The target of rapamycin (TOR) kinase is an evolutionarily conserved hub of nutrient sensing and metabolic signaling. In plants, a functional connection of TOR activation with glucose availability was demonstrated, while it is yet unclear whether branched-chain amino acids (BCAAs) are a primary input of TOR signaling as they are in yeast and mammalian cells. Here, we report on the characterization of an Arabidopsis mutant over-accumulating BCAAs. Through chemical interventions targeting TOR and by examining mutants of BCAA biosynthesis and TOR signaling, we found that BCAA over-accumulation leads to up-regulation of TOR activity, which causes reorganization of the actin cytoskeleton and actin-associated endomembranes. Finally, we show that activation of TOR is concomitant with alteration of cell expansion, proliferation and specialized metabolism, leading to pleiotropic effects on plant growth and development. These results demonstrate that BCAAs contribute to plant TOR activation and reveal previously uncharted downstream subcellular processes of TOR signaling.