Damage-associated molecular patterns (DAMPs) are endogenous molecules that can activate the plant innate immunity. DAMPs can derive from the plant cell wall, which is composed of a complex mixture of cellulose, hemicellulose, and pectin polysaccharides. Fragments of pectin, called oligogalacturonides (OG), can be released after wounding or by pathogen-encoded cell wall degrading enzymes (CWDEs) such as polygalacturonases (PGs). OG are known to induce innate immune responses, including the activation of mitogen-activated protein kinases (MAPKs), production of H2O2, defense gene activation, and callose deposition. Thus, we hypothesized that xyloglucans (Xh), derived from the plant cell wall hemicellulose, could also act as an endogenous elicitor and trigger a signaling cascade similar to OG. Our results indicate that purified Xh elicit MAPK activation and immune gene expression in grapevine (Vitis vinifera) and Arabidopsis (Arabidopsis thaliana) to trigger induced resistance against necrotrophic (Botrytis cinerea) or biotrophic (Hyaloperonospora arabidopsidis) pathogens. Xh also induce resveratrol production in grapevine cell suspension and callose deposition in Arabidopsis which depends on the callose synthase PMR4. In addition, we characterized some signaling components of Xh-induced immunity using Arabidopsis mutants. Our data suggest that Xh-induced resistance against B. cinerea is dependent on the phytoalexin, salicylate, jasmonate, and ethylene pathways.

SummaryIn a preceding microcosm study, we found huge differences in phosphorus (P) acquisition in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) sharing a common mycorrhizal network (CMN). Is the transcriptional regulation of arbuscular mycorrhizal (AM)-induced inorganic orthophosphate (Pi) transporters responsible for these differences?We characterized and analyzed the expression of Pi transporters of the Pht1 family in both plant species, and identified two new AM-inducible Pi transporters in flax.Mycorrhizal Pi acquisition was strongly affected by the combination of plant and AM fungal species. A corresponding change in the expression of two AM-inducible Pht1 transporters was noticed in both plants (SbPT9, SbPT10, LuPT5 and LuPT8), but the effect was very weak.Overall, the expression level of these genes did not explain why flax took up more Pi from the CMN than did sorghum. The post-transcriptional regulation of the transporters and their biochemical properties may be more important for their function than the fine-tuning of their gene expression.