Trichoderma gamsii affected herbivore feeding behaviour on Arabidopsis thaliana by modifying the leaf metabolome and phytohormones

Abstract

Plants can re-programme their transcriptome, proteome and metabolome to deal with environmental and biotic stress. It has been shown that the rhizosphere microbiome has influence on the plant metabolome and on herbivore behaviour. In the present study, Trichoderma gamsii was isolated from Arabidopsis thaliana rhizosphere soil. The inoculation of roots of Arabidopsis thaliana with T. gamsii significantly inhibited the feeding behaviour of Trichoplusia ni and affected the metabolome as well as the content of phytohormones in Arabidopsis leaves. T. gamsii-treated plant leaves had higher levels of amino acids and lower concentrations of sugars. In addition, T. gamsii-treated plant leaves had more abscisic acid (ABA) and lower levels of salicylic acid (SA) and indole-3-acetic acid (IAA) in comparison with the untreated plants. Furthermore, the inoculation with T. gamsii on different signalling mutants showed that the induction of defences were SA-dependent. These findings indicate that T. gamsii has potential as a new type of biocontrol agent to promote plant repellence to insect attacks.

Figure 1

Larval gained weight of Trichoplusia ni fed for 24 h on four‐week‐old Arabidopsis plants amended with soil microbiomes. The control treatment received only Hoagland's solution. Each treatment had 18 pots (repetitions) and each pot contained one plant. The values represent the means ± SEM. Bars with dissimilar letters are significantly different (P < 0.05; Tukey's honest significance test).

Figure 2

Larval gained weight of Trichoplusia ni fed for 24 h on four‐week‐old Arabidopsis Col‐0 plants amended with fungal isolate F18. The control treatment received only Hoagland's solution. Each treatment had 18 pots and each pot contained four plants. This experiment was repeated four times. All experiments showed the same trend. Data in this figure represent the results of one experiment. The values represent the means ± SEM. The asterisk above the bar indicates significance relative to the control at p < 0.05 level (t‐test).

Figure 3

Leaf metabolites of Arabidopsis analysed by GC‐MS. A. Principal Component Analysis (PCA) of the leaf metabolites of Arabidopsis inoculated with and without T. gamsii F18. B. Metabolomics features detected by GC‐MS were categorized into six groups to generate a cumulative peak height for each group. The six groups included sugar, sugar alcohols, amino acid, phenolics, other compounds (fatty acid, amide and amine) and unknown (uncategorized compounds). The values represent the means SEM. The asterisks above the bars indicate significance relative to the control at P < 0.05 level (t‐test). C. Fold change of amino acids in T. gamsii F18‐treated leaves compared with control plants.

Figure 4

Larval gained weight of Trichoplusia ni fed for 24 h on four‐week‐old Arabidopsis Col‐0, ein2‐1, NahG and sid2‐1 plants amended with T. gamsii F18 a week prior to insect herbivory. The control treatment received only Hoagland's solution. The values represent the means ± SEM. The asterisks above the bars indicate significance relative to the control at P < 0.05 level (t‐test).