A putative auxin efflux carrier FgAec1 contributes to the pathogenicity of Fusarium graminearum.

BACKGROUND: Auxin is crucial for plant growth and influences plant-pathogen interactions. Pathogen-produced indole-3-acetic acid (IAA) is crucial for pathogenicity; however, the role of plant-derived or pathogen-derived IAA in regulating plant defense responses remains poorly understood. RESULTS: In this study, two putative auxin efflux carrier (AEC) proteins, FgAec1 and FgAec2, were identified in Fusarium graminearum. To study the effects of the pathogen-derived auxins on Fusarium head blight (FHB), knockout mutants of FgAec1 or FgAec2 showed no effect on vegetative growth or conidia morphology. However, the Δfgaec1 mutant (but not the Δfgaec2 mutant) exhibited reduced growth and development in wheat spikes, indicating that FgAec1 is a key pathogenic factor. Deletion of FgAec1 reduced auxin efflux during the wheat-F. graminearum interaction, whereas exogenous auxin restored the pathogenicity of Δfgaec1 in wheat spikes. Knockout of FgAec1 enhanced the salicylic acid (SA)-mediated defense signaling pathway in response to F. graminearum. Additionally, deletion of a nitrilase FgNIT2 gene, involved in IAA synthesis in F. graminearum, reduced fungal pathogenicity and affected the expression of the SA-responsive genes in wheat treated with F. graminearum. The SA-deficient taics-AB mutant plant inoculated with Δfgaec1 demonstrated that a reduction in the auxin pool may increase the plant's resistance to the Δfgaec1 strain by disrupting the balance of auxin-SA crosstalk. CONCLUSIONS: These results indicate that FgAec1 may act as a putative AEC, regulating auxin transport in F. graminearum and mediating F. graminearum-wheat interactions. These findings provide new insights into the role of auxin biosynthesis in F. graminearum in suppressing host plant defenses.