Interactions between zinc and Phomopsis longicolla infection in the roots of Glycine max
Abstract To reveal the role of zinc in plant-pathogen interactions, soybean seedlings were grown hydroponically with a range of Zn concentrations, 0.06 (deficient, Zn0), 0.4 (optimal growth), 1.5, 4, 12 and 38 μM (toxic), and were subsequently inoculated with Phomopsis longicolla via the roots. P. longicolla is a hemi-biotroph fungus causing significant soybean yield loss worldwide. In vivo analyses of metal tissue-distribution by micro-X-ray fluorescence showed local Zn mobilization in the root maturation zone in all treatments 14 days post infection. Decreased root and pod biomass, and photosynthetic performance in infected Zn0.4 plants were accompanied by root Zn, jasmonoyl-L-isoleucine (JA-Ile), jasmonic acid, and cell wall-bound syringic acid (cwSyA) accumulation. In the Zn1.5 treatment, 7-fold higher root Zn concentration, JA-Ile, cwSyA, cell wall-bound vanilic acid and leaf jasmonates contributed to maintaining of photosynthesis and pod biomass under infection. Host-pathogen nutrient competition and phenolics accumulation could limit the infection in Zn-deficient plants. The low infection rate in Zn4-treated roots correlated with salicylic and 4-hydroxybenzoic acid, and cell wall-bound p-coumaric acid accumulation. Zn toxicity promoted pathogen invasion and depleted cell wall-bound phenolics. The results show that manipulation of Zn availability may improve soybean resistance to P. longicolla by stimulating phenolics biosynthesis and stress-inducible phytohormones.