The microbiome of the leaf surface protects against disease. Leaf microbiome

We explored the importance of bacteria from the phyllosphere in the resistance of plants to pathogens. Cuticle mutants of Arabidopsis thaliana that are highly resistant to the fungal pathogen Botrytis cinerea were inoculated under gnotobiotic conditions. Under non-sterile natural conditions, bdg (bodyguard) or lacs-2 (long chain fatty acid synthase2) display a strong resistance to the fungal pathogen Botrytis cinerea. Under gnotobiotic conditions, bdg mutants were equally susceptible as WT (wild type) plants whereas lacs-2 mutants retained the resistance. When bacteria were washed off leaf surfaces and sprayed on the corresponding sterile plants prior to inoculation, the resistance of bdg mutants could be restored whereas lacs2.3 plants remained resistant. Thus, microbes present on the surface of bdg mutants are likely to play a role in the resistance to B. cinerea, whereas the resistance of lacs-2 mutants results from an endogenous mechanism. Applying bacteria from washed surfaces of WT, bdg or lacs2.3 on non-sterile WT Col-0 plants could also increase resistance, providing a high concentration of bacteria was applied. The bacterial population harbored on the surface of WT, bdg and lacs-2 mutants was compared using 16S ribosomal DNA sequencing and showed distinct populations between WT plants and cuticle mutants, but the populations on the cuticle mutants could not be distinguished. One bacterium was isolated fro surface washes of bdg and high coverage sequencing identified it as a P. x. When applied alone, P. x. provided resistance to WT Col-0 plants under gnotobiotic conditions as well under natural non-sterile conditions. These results open new perspectives on our perception of the phyllosphere in the resistance of plants.