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Plant nitrogen (N) fertilization is known to affect disease; however, the underlying mechanisms remain mostly unknown. We investigated the impact of N supply on the Arabidopsis thaliana-Botrytis cinerea interaction. A. thaliana plants grown in low nitrate were more tolerant to all wild-type B. cinerea strains tested. We determined leaf nitrate concentrations and showed that they had a limited impact on B. cinerea growth in vitro. For the first time, we performed a dual RNA-Seq of infected leaves of plants grown with different nitrate concentrations. Transcriptome analysis showed that plant and fungal transcriptomes were marginally affected by plant nitrate supply. Indeed, only a limited set of plant (182) and fungal (22) genes displayed expression profiles altered by nitrate supply. The expression of selected genes was confirmed by quantitative reverse transcription PCR at 6 hr postinfection (hpi) and analysed at a later time point (24 hpi). We selected three of the 22 B. cinerea genes identified for further analysis. B. cinerea mutants affected in these genes were less aggressive than the wild-type strain. We also showed that plants grown in ammonium were more tolerant to B. cinerea. Furthermore, expression of the selected B. cinerea genes in planta was altered when plants were grown with ammonium instead of nitrate, demonstrating an impact of the nature of N supplied to plants on the interaction. Identification of B. cinerea genes expressed differentially in planta according to plant N supply unveils two novel virulence functions required for full virulence in A. thaliana: a secondary metabolite (SM) and an acidic protease (AP)., (© 2020 The Authors. Molecular Plant Pathology published by British Society for Plant Pathology and John Wiley & Sons Ltd.)

Few secreted proteins involved in plant infection common to necrotrophic bacteria, fungi and oomycetes have been identified except for plant cell wall-degrading enzymes. Here we study a family of iron-binding proteins that is present in Gram-negative and Gram-positive bacteria, fungi, oomycetes and some animals. Homolog proteins in the phytopathogenic bacterium Dickeya dadantii (IbpS) and the fungal necrotroph Botrytis cinerea (BcIbp) are involved in plant infection. IbpS is secreted, can bind iron and copper, and protects the bacteria against H 2 O 2 -induced death. Its 1.7 Å crystal structure reveals a classical Venus Fly trap fold that forms dimers in solution and in the crystal. We propose that secreted Ibp proteins binds exogenous metals and thus limit intracellular metal accumulation and ROS formation in the microorganisms.

Mature grapevine berries at the harvesting stage (MB) are very susceptible to the gray mold fungus Botrytis cinerea, while veraison berries (VB) are not. We conducted simultaneous microscopic and transcriptomic analyses of the pathogen and the host to investigate the infection process developed by B. cinerea on MB versus VB, and the plant defense mechanisms deployed to stop the fungus spreading. On the pathogen side, our genome-wide transcriptomic data revealed that B. cinerea genes upregulated during infection of MB are enriched in functional categories related to necrotrophy, such as degradation of the plant cell wall, proteolysis, membrane transport, reactive oxygen species (ROS) generation, and detoxification. Quantitative-polymerase chain reaction on a set of representative genes related to virulence and microscopic observations further demonstrated that the infection is also initiated on VB but is stopped at the penetration stage. On the plant side, genome-wide transcriptomic analysis and metabolic data revealed a defense pathway switch during berry ripening. In response to B. cinerea inoculation, VB activated a burst of ROS, the salicylate-dependent defense pathway, the synthesis of the resveratrol phytoalexin, and cell-wall strengthening. On the contrary, in infected MB, the jasmonate-dependent pathway was activated, which did not stop the fungal necrotrophic process.