Fig 1: Excess AAs in lht1 exudates combined with Ps WCS417r inhibit wild-type Arabidopsis growth. Across all panels, each dot represents an independent biological replicate. The median of all biological replicates is depicted as a bar. A two-sided Student’s t-test was performed for statistical comparison of two means or a Welch’s t-test for two means with unequal variances. For comparison of more than two means, a one-way ANOVA followed by Tukey’s posthoc test, or a Kruskal–Wallis test for unequal variances followed by Dunn’s posthoc test was performed. The p-values are represented as * ≤0.05, ** ≤0.01, *** ≤0.005, and **** ≤0.001. Further experimental and analysis details are described in Section 5. (A) The lht1 exudates inhibit the growth of wild-type Arabidopsis when inoculated with Ps WCS417r. Fifteen-day-old wild-type seedlings growing on 12-well plates with floating mesh on WT or lht1 exudate with or without Ps WCS417r OD600nm = 0.2. Each dot represents the median weight of ≥3 seedlings per condition. The experiment was repeated 6 times; the median of all biological replicates is depicted as a bar. (B) Gln-supplemented WT exudates combined with Ps WCS417r inhibit the growth of wild-type Arabidopsis. Assay was carried out as in (A), except that two different Ps WCS417r inoculum titters were used (OD600nm = 0.2 or 1.6) and that WT exudates were supplemented with Gln 1mM or 10 mM and either inoculated or not with Ps WCS417r (OD600nm = 0.2). (C) Ser-supplemented WT exudates directly inhibit the growth of wild-type Arabidopsis. Assay and controls are shown in (B), except for WT exudates that were supplemented with 1 mM or 10 mM Ser (instead of Gln). (D) Pathogen-responsive genes are not induced in plants concomitantly exposed to Ps WCS417r and lht1 exudates. Wild-type seedlings were exposed for 24 h to WT exudate (depicted as WT mock), WT exudate + Ps WCS417r (final OD600nm = 0.2), lht1 exudate (depicted as lht1 mock), or lht1 exudate + Ps WCS417r (final OD600nm = 0.2), as described here in (A) and in Methods. Gene expression in the roots was assessed using RT-qPCR. Fold change was calculated using ∂∂Ct. The specific comparisons are depicted in the X-axis. Each dot corresponds to an independent biological replicate (calculated based on 2 experimental replicates), and the median of the 3 biological replicates is depicted as a bar. (E) GH3.3, a mediator of the stress-triggered growth inhibition response, is induced in plants concomitantly exposed to Ps WCS417r and lht1 exudates. Expression of the gene encoding the auxin-conjugating enzyme GH3.3 is measured in the conditions described in (D). (F) Ps WCS417r produces more ammonia from lht1 than from wild-type exudates. Ammonia excreted by Ps WCS417r while incubated on WT or lht1 exudates was assessed at 0, 5, 10, 20, and 30 min. Exudates obtained in three independent experiments were assessed for ammonia independently but simultaneously. After the indicated times, the incubation media supernatants were harvested, filter sterilized, and their ammonia content was assessed using an ammonia assay kit (AbCam; Cat # ab102509) following manufacturer’s guidelines. Each dot represents the median ammonia concentration (µmol/mL), and error bars correspond to the SEM.