FIG 4 .

Phenotypes of praR and/or rebR mutants. S. rostrata plants were inoculated with the WT or ΔpraR, ΔrebR, or ΔpraR ΔrebR mutant strains and grown at 30°C, and stem nodules were analyzed at 14 dpi. (A) Hand-cut images (upper) and ARAs (lower) of stem nodules. Values are presented as means ± standard deviations from five separate plants. Different letters indicate significant differences (P < 0.05, Tukey-Kramer). (B) OM observations of infected host cells in stem nodules and TEM observations of harbored bacterial cells. (C) Relative expression levels of the reb operon in stem nodules and free-living cultures. Total RNAs were isolated from bacteria residing in stem nodules and from bacterial cultures after growth to an OD₆₀₀ of approximately 1.0 at 38°C. Expression levels of the reb operon were estimated using quantitative RT-PCR and were normalized to 16S rRNA. Data are presented as means ± standard deviations of three replicate cultures and plants and are expressed relative to mRNA levels in free-living WT cultures. Statistical analyses were carried out for stem nodules and free-living cultures, respectively. Different letters indicate significant differences (P < 0.05; Tukey-Kramer).