Broccoli
Similar to Arabidopsis, inoculation of Broccoli roots with each of the
three rhizobacterial strains resulted in substantial alteration of the
shoot metabolome. From the 1908 detected metabolites, 933 (49%) were
significantly different between at least two treatments. For this set of
metabolites, HCA revealed eight distinct metabolite clusters of the host
metabolome. PCA further showed that the metabolome of Broccoli seedlings
inoculated with different rhizobacteria is clearly different from the
control and from each other. The first three PCs explained 84% of the
total variance (Figure 2c1 ). PC1, representing 47% of the
total variance, was associated with metabolites that discriminate both
the control and MB samples from the Pbg and Pf SS101
samples. These metabolites were either significantly increased or
decreased in plants inoculated by Pbg or Pf SS101
(Figure 2c2 decreased cluster 3 and induced clusters6 and 7 ) that represent effective and ineffective
partnerships with the host, respectively. The indole glucosinolate
glucobrassicin also showed a significant increase in plants inoculated
with Pbg and Pf SS101. PC2 explained 22% of the total
variance and corresponded to metabolites that were either specifically
altered in the Pbg or Pf SS101 treatments (Figures
2c1 and 2c2 induced (clusters 8 (Pf SS101) and9 (Pbg )) or reduced by Pbg inoculation (cluster4 )). Metabolites that were specifically induced in the
ineffective partnership between Pf SS101 and the host were
dominated by flavonoids such as kaempferol, quercetin glycosides and
glucosinolates including glucoibervirin, neoglucobrassicin and
4-methoxyglucobrassicin. Furthermore, several hydroxycinnamates
conjugated or not with quinic acid, including chlorogenic acid
(caffeoyl-quinic acid), coumaroyl quinic acid, sinapic acid and ferulic
acid, were predominant in those metabolite clusters (clusters 7and 8 ). PC3 explained 15% of the total variation and
corresponded to MB-induced metabolites represented in cluster 1and induced metabolites by all three rhizobacteria in cluster2 . Hexose 1-phosphate in cluster 1 showed a
MB-specific increase. Meanwhile, some of the putatively annotated
metabolites in cluster 2 including tryptophan, a precursor of
indole glucosinolates, was reduced by all three rhizobacterial
treatments.