Fig. 4: Enhanced BSB synthesis correlates with an AM symbiosis permissive state.

a Increased transcript level of the SL biosynthesis genes, MpaD27, MpaCCD7, MpaCCD8A, MpaCCD8B and MpaMAX1, of M. paleacea, and AaCCD8 of Anthoceros agrestis under phosphate starvation. Plants were grown on half-strength Gamborg’s B5 medium with (+P) or without (−P) phosphate. Data are means ± SD (n = 3 biologically independent samples) and p values in Welch’s t-test, two tailed are indicated. b Identification of DEGs under phosphate starvation and in Mpaccd8a/8b mutants by RNA-seq analysis. Left: Venn diagram of genes down-regulated in −P condition compared to +P condition in WT (blue) and up-regulated in Mpaccd8a/8b compared to WT (pink). Right: Venn diagram of genes up-regulated in −P compared to +P condition in WT (blue) and down-regulated in Mpaccd8a/8b compared to WT (pink). c Heatmap of gene transcript level under phosphate deficiency in M. paleacea. DEGs (logFC > 1) up-regulated under –P are underlined. d Increase in the stimulation activity of the exudate of M. paleacea on seed germination of Orobanche minor under phosphate starvation. Exudates from M. paleacea grown on +P and −P medium were used for analysis. Data are means ± SD (n = 4 biologically independent samples). e Low phosphate allows mycorrhizal colonization. M. paleacea inoculated with Rhizophagus irregularis were watered with long ashton solutions containing 0.015, 0.5, 1 or 2.5 mM phosphate. Right: Cleared thalli of M. paleacea grown in low phosphate (bottom right) show a higher level of fungal colonization (marked by a natural purple pigment) than thalli grown at high phosphate (upper right). The exclusion zone which is the distance between the notch (harrow) and the end of the colonized zone (yellow asterisk) was measured (n ≥ 15 biologically independent plants). Box plot shows first quartile, median, third quartile, whiskers 1.5 interquartile. p values (one-way ANOVA, post hoc Tukey) are shown. f Developmental stage-dependent induction of MpaCCD8B transcript level in response to low phosphate conditions. Gemmalings of 1–3 weeks after inoculation (wai) were transferred to media containing different concentrations of phosphate. Data are means ± SD (n = 3 biologically independent samples) and the HSD test was used for multiple comparisons. Statistical differences (p values < 0.05) are indicated by different letters.