Fig. 5
Isoquinoline alkaloids are involved in CSR disease suppression. a Heatmap showing the expression trends of genes involved in the selected functional pathways. * represents a significant difference (P < 0.05) compared to the CK group. b Relative expression levels of maize TYDC1, as determined by RT-qPCR. The values are means ± SDs (n = 3). Significant differences (P < 0.05) were calculated by one-way ANOVA and are shown with different lowercase letters. c PCoA based on Bray–Curtis distance matrices of maize RS (left) and RE (right) metabolites in CSR-resistant and CSR-susceptible groups. d Normalized concentrations of berberine (BBR), isoquinoline, and l-phenylalanine in RE compartment, as determined by LC–MS/MS. e Inhibitory effects of 5% (v/v) DMSO (CK) and 5, 25, 50, and 100 µg/mL berberine on mycelial growth (upper panels) and 25 µg/mL berberine on disease severity (lower panels). f Disease severity (as mean ± SD) of maize seedlings treated with Fg (105 spores/mL, CK) and additional berberine (25 µg/mL, BBR). g Proposed model of the microbial assembly across different CSR resistance and compartments challenged with Fusarium CSR. Maize cultivars resistant to CSR reshape the microbiota and recruit three types of Bacillus species (SC-I, inhibition by pre-emption; SC-II, inhibition by potential secretion of antimicrobial compounds; and SC-III, no direct inhibition but induction of berberine biosynthesis by the host), conferring benefits in disease suppression. SC-III facilitates berberine biosynthesis by inducing the expression of TYDC, encoding an enzyme that catalyzes the production of dopamine from l-dopa and tyramine. These beneficial Bacillus can be recruited from the rhizosphere soil (RS) compartment via the root endosphere (RE) compartment to the stem endosphere (RE) compartment, but not to the grain endosphere (GE) compartments