Bacteria-originated AHL molecules prime Col-0 but not mutants deficient in JA-signaling. Roots of 6-week-old Arabidopsis plants were drenched three times with four AHL-producing bacteria: S. plymuthica HRO-C48, R. etli CFN42, B. graminis DSM17151, and S. meliloti Rm2011 (wild-type strains). AHL-negative strains, expressing the lactonase AttM from the plasmid pBBR2-attM, were used as bacterial control (attM strains) in addition to 10 mM MgCl2 used as solvent control. Leaves were subsequently infiltrated with Pst, OD600 = 0.01 (107 CFU/ml) in 10 mM MgCl2. Bacterial proliferation was assessed by enumeration of CFUs, 2 and 96 h after infiltration. Bacterial growth rate was calculated accordingly. Inoculation with AHL-producing bacteria enhanced resistance against Pst in Col-0 plants, as revealed by the lower pathogen growth rate, whereas AHL-negative bacteria could not induce this effect (A). However, lox2, jar1-1, tga2/5/6, and coi1-16 mutants revealed no difference in the bacterial growth rate. Boxes represent the interquartile range between the first and the third quartile and the middle line marks the median, whiskers indicate 1.5× interquartile range, points indicate outliers. Statistical analysis was performed by Student's t-test, *P < 0.05, **P < 0.01, ****P < 0.0001, n ≥ 3. Representative infected leaves of wild-type Col-0 and jar1-1 were collected 96 h after the Pst infiltration from all three treatments (B). The bar indicates 1 cm.
