Figure 1.

Hierarchical clustering of M. truncatula genes differentially regulated during symbiotic interactions with S. meliloti. The expression patterns of 539 genes found as differentially regulated in Mt6k-RIT macroarray hybridizations were analyzed under 10 symbiotic conditions, and ratios were calculated between the inoculated and the corresponding noninoculated samples. All genes exhibit a minimum 2-fold expression ratio with a P value ≤0.05 in at least one condition. Whole root systems from wild-type Jemalong A17 (J), supernodulating mutant TR122 (T), and nfp and hcl mutants were harvested at 3 or 6 dpi with either wild-type (W3, W6) or nodA (A3, A6) S. meliloti strains and compared to noninoculated material (0). Isolated nodules were collected at 4 (N4) and 10 dpi (N10) and compared to noninoculated roots (N0). Hierarchical clustering was carried out using average linkage values and Pearson correlations. The global clustering analysis is presented in (A), where five clusters (designated I–V) can be distinguished. Close-ups of clusters I and II, respectively, are shown in B and C, with corresponding MtC EST cluster numbers and annotations.