Grapevine colonization by endophytic bacteria shifts secondary metabolism and suggests activation of defense pathways

Aims The colonization pattern of three grapevine endophytes (families Sphingomonadaceae and Enterobacteriaceae) and their putative metabolic signature in plants were analyzed on Vitis vinifera L. cv. Pinot noir to determine the behavior of endophytic strains inside plants as well as how plants respond to such microsymbionts. Methods Strains Enterobacter ludwigii EnVs6, Pantoea vagans PaVv7 and Sphingomonas phyllosphaerae SpVs6, were root inoculated on micropropagated grapevine plantlets and colonization was determined by double labeling of oligonucleotide probes-fluorescence in situ hybridization (DOPE-FISH) coupled with confocal microscopy. After inoculation, the metabolic signature in plants colonized by Enterobacter ludwigii EnVs6 was further studied using UPLC//tandem mass spectrometry analysis. Results E. ludwigii EnVs6 and P. vagans PaVv7 colonized the plantlets and were both observed on the root surfaces and as endophytes in the cortex and inside the central cylinder up to xylem vessels, but not in the systemic plant parts. Strain SpVs6 also efficiently colonized the root surface, but not the endorhiza and was therefore not detected as an endophyte. A metabolic signature in plants inoculated with E. ludwigii EnVs6 was depicted, resulting in a significant increase in vanillic acid and a decrease in the concentration of catechin, esculin, arbutin, astringin, pallidol, ampelopsin, D-quadrangularin and isohopeaphenol. Changes in the concentration of epicatechin, procyanidin 1, taxifolin and the sum of quercetin-3-glucoside and quercetin-3-galactoside, in roots and stems were also detected, showing that the effect of colonization of plants is most prominent in the stems. Conclusions Colonization patterns in endophytes are divergent according to the strains used. A metabolic signature suggests the activation of pathways involved in plant defense but also modulation of the production of metabolites that are keys for colonization.