*4.2. Bacterial Strain and Growth Conditions*

*Pseudomonas syringae* van Hall 1902, CECT321 (Pph) was grown for two days at 30 ◦C on liquid King's B (KB) medium at 220 rpm. For infection experiments, a final concentration of 10<sup>8</sup> CFU/mL Pph was used. The Pph solution for inoculation was prepared by removing the media by centrifugation and resuspending in the same volume of sterile water, as indicated in De la Rubia et al. (2021) [47].

#### *4.3. Elicitation, Pathogen Inoculation, and Sample Preparation*

Leaves from common bean plants at V1 stage (with two cotyledonary leaves expanded, but not the true leaves developed) were sprayed with 2 mL per leaf of 100 μM 2,6-dichloropyridine-4-carboxylic acid (INA, Alfa Aesar, LOT: 10160271) (INA) or sterile water (Mock), as described in Martínez-Aguilar et al. [49]. After 7 days, some plants previously treated or not with INA were sprayed with 2 mL of the Pph solution on foliage leaves, resulting in Mock + Pph and INA + Pph treatments. All plants were grown for 7 more days and then the foliage leaves of 10 plants per treatment were collected and homogenized with liquid nitrogen to form a pool for each condition. All pools were stored at −80 ◦C until their use. Three complete independent experiments (*n* = 3) were performed (see Supplementary Figure S1A).

#### *4.4. Reactive Oxygen Species Detection*

The ROS production was determined in V1 plants leaf disks using the luminol assay [100] in a Multi-Detection Microplate Reader Synergy HT (BioTek). Leaf disks were transferred to a multi-well plate (see Supplementary Figure S1B), containing 200 μL water or 100 μM INA, and they were incubated overnight. Afterwards, the previous solution was removed, and 100 μL per well of a solution containing 20 μM luminol L-012 (Wako) and 100 μg/mL peroxidase from horseradish type VI.A (Sigma, P6782) were added, and incubated in the dark for 30 min. Then, the reactions were started by adding 100 μL of water (Mock condition) as negative control, 100 μL of 2 μM flg22 (flg22 condition) as positive control, 100 μL of 200 μM INA (INA condition), and 100 μL of 2 μM flg22 to those disks previously incubated overnight with 100 μM INA (preINA + flg22). The ROS production, measured as relative luminescent units (RLUs), was measured over 90 min, with an integration time of 0.6 s. Data shown represent mean ± SE from one representative experiment of three independent ones performed with similar results (see Supplementary Figure S1A). The total areas under the kinetic curves were integrated, and the resulting values were statistically analyzed by One way ANOVA (*p* < 0.05), post hoc Tukey test.
