Arabidopsis thalianaZn2+-efflux ATPases HMA2 and HMA4 are required for resistance to the necrotrophic fungusPlectosphaerella cucumerinaBMM

SUMMARY Zinc is an essential nutrient at low concentrations, but toxic at slightly higher ones. This could be used by plants to fight pathogens colonization. Elemental distribution in Arabidopsis thaliana leaves inoculated with the necrotrophic fungus Plectosphaerella cucumerina BMM ( PcBMM ) was determined and compared to mock-inoculated ones. Infection assays were carried out in wild type and long-distance zinc trafficking double mutant hma2hma4 , defective in root-to-shoot zinc partitioning. Expression levels of genes involved in zinc homeostasis or in defence phytohormone-mediated pathways were determined. Zinc and manganese levels increased at the infection site. Zinc accumulation was absent in hma2hma4. HMA2 and HMA4 transcription levels were upregulated upon PcBMM inoculation. Consistent with a role of these genes in plant immunity, hma2hma4 mutants were more susceptible to PcBMM infection, phenotype rescued upon zinc supplementation. Transcript levels of genes involved in the salicylic acid, ethylene and jasmonate pathways were constitutively upregulated in hma2hma4 plants. These data are consistent with a role of zinc in plant immunity not only of hyperaccumulator plants, but also of plants containing ordinary levels of zinc. This new layer of immunity seems to run in parallel to the already characterized defence pathways, and its removal has a direct effect on pathogen resistance.