Chemical armed allies promote plant resistance to pathogen: The contribution of arbuscular mycorrhizal fungi to an invasive weed.

Invasive weeds often possess strong resistance to biotic stresses, which causes huge ecological problems. Both plant growth regulators (PGRs) and arbuscular mycorrhizal (AM) fungi contribute to plant growth and resistance. However, their combined interactions in invasive plants' defense remain poorly understood. To address this knowledge gap, the invasive weed Alternanthera philoxeroides was treated with gibberellins (GA) and paclobutrazol (PAC), inoculated with Clariodeoglous etunicatum to test its response to pathogenic fungi. We found that these two PGRs suppressed AM fungi colonization. Both GA and AM fungi significantly promoted aboveground plant growth, while the two PGRs and AM fungi reduced pathogen infection. Metabolite analysis revealed that AM fungi inoculation significantly elevated vanillic acid, gentisic acid, and pomiferin content. Moreover, flavone, organic acid, and amino acids were positively related with plant growth, while jasmonic acid and amino acids were correlated with plant resistance. Our findings provide direct evidence that, through PGRs and metabolites, AM fungi could be "chemical armed" and contribute to plant growth and resistance to pathogens. These findings offer new insights into how PGRs and AM fungi modulate metabolites to enhance invasive plants' resistance, which might contribute to understanding the mechanism of plant invasion and weed management in agro-ecosystem.