Figure 4.

C. tofieldiae Colonization Induces Expression of A. thaliana Pht1 Pi Transporter Genes

(A) Transcript profiling of 19 A. thaliana phosphate transporter genes and PHF1 in colonized and mock-treated roots under Pi-limiting (low P: [50 μM]) or Pi-sufficient (high P: [625 μM]) conditions at 6, 10, 16, and 24 dpi. Overrepresented (yellow to red) and underrepresented transcripts (yellow to blue) are shown as log2 fold changes relative to the mean expression measured across all stages. Log2-transformed expression levels (white to red) are also depicted for each sample. Significantly regulated genes (|log2FC| >1, FDR <0.05) are highlighted in purple (upregulated) to green (downregulated). Note that two Pht transporter genes were strongly induced at late stages of C. tofieldiae (Ct) colonization (asterisks).

(B) Quantitative analysis of shoot fresh weight (SFW) of PSR regulatory mutants under Pi-deficient conditions. SFW was measured at 30 dpi from at least 15 plants per treatment, per experiment. Results of three independent experiments were combined. An ANOVA and subsequent Tukey HSD test were conducted to evaluate whether the fold-change in SFW between Ct- and mock-inoculated (M) plants (calculated as SFW Ct/SFW Mock) was significantly different (^∗p < 0.01) between genotypes (Col-0: 1.45-fold versus phf1: 1.23-fold).

(C) Transcript profiling of 61 Ct genes significantly regulated between Ct- and mock-inoculated roots under Pi-deficient (low Pi: [50 μM]) or Pi-sufficient (high Pi: [625 μM]) conditions at 6, 10, 16, and 24 dpi. Overrepresented (yellow to red) and underrepresented transcripts (yellow to blue) are shown as log2 fold changes relative to the mean expression measured across all stages. Significantly regulated genes (|log2FC| >1, FDR <0.05) are highlighted in purple (upregulated) to green (downregulated). Arrows indicate the two most highly upregulated genes: phosphate H⁺symporter (CT04_05366, gray) and acid phosphatase (CT04_08450, black). The right part of the heatmap depicts the functional categories to which genes belong. CSEPs, candidate secreted effector proteins; CAZymes, carbohydrate active enzymes.

See also Figure S4.