Arabidopsis
Inoculation of Arabidopsis roots with each of the three rhizobacteria resulted in significant changes in the shoot metabolome. From the 725 detected metabolites, 465 (64%) were significantly different between at least two treatments. In the PCA, the first three principal components explained 89% of the total variance (Figure 2a1 ). The first principal component (PC1), representing 56% of the total variance, was associated with metabolites that were highly induced (Figure 2a2 clusters 5 ; 291 metabolites and 6 ; 10 metabolites) or reduced in the ineffective partnership betweenPbg and Arabidopsis (clusters 3 ; 82 metabolites and4 ; 33 metabolites). Pbg -induced metabolites in cluster5 primarily encompassed flavonoids including anthocyanins (cyanidin rutinoside, delphinidin rutinoside), tryptophan and its derivatives such as IAA, defense or stress-associated metabolites such as salicylic acid, dihydroxybenzoic acid glucosides, copoline and camalexin. The second principal component (PC2) explained 21% of the total variance and corresponded to metabolites that were increased (Figures 2a1 and a2 clusters 2 ; 18 metabolites and6 ; 9 metabolites) or decreased (cluster 7 ; 10 metabolites) in the effective partnership of Arabidopsis with PfSS101 and MB. Among the identified metabolites, the long-chain aliphatic glucosinolate glucohirsutin (8-(methylsulfinyl)octyl glucosinolate) was significantly increased in Arabidopsis shoot after inoculation with Pf SS101 or MB. From the same group of glucosinolates, 8-(methylthio) octyl glucosinolate was significantly increased after inoculation with Pf SS101 (Supplementary Material, Table S4 ). The third principal component (PC3) explained 12% of the total variation and was represented by metabolites that accumulated only after inoculation with either Pf SS101 or MB (Figures 2a1 and 2a2 cluster 1 ; 8 metabolites and cluster 9 ; 7 metabolites, respectively). A fatty acyl glycoside demonstrated Pf SS101-specific accumulation while fumaric acid displayed MB-specific increases.