Sweet specificities of the root extracellular trap of perennial ryegrass (Lolium perenne), a fructan accumulating plant.

Perennial ryegrass (Lolium perenne) is a fructan-accumulating plant constituting one of the most important grassland species with high herbage production, nutritive value and digestibility for grazing cattle. Although fructans were reported to be involved in plant defense acting as antioxidants or stress signals, their contribution in root protection is still to be explored. In roots, atypical defense is provided by the "Root Extracellular Trap" or "RET" at the root-soil interface. The molecular composition and structural organization of the RET are essential to provide root defense against pathogen attacks and abiotic stresses. The RET was reported to be mainly composed of polysaccharides (homogalacturonan, xylogalacturonan, xyloglucan) and proteoglycans such as arabinogalactan proteins (AGPs). Our aim is to characterize the RET composition of L. perenne using cell imaging techniques and a wide range of monoclonal antibodies directed against epitopes from cell wall glycomolecules and to investigate the potential presence of fructans. Interestingly, we found that both mucilage and cell wall surface of border cells were enriched in AGP epitopes. An increased amount of the AGP-containing mucilage was produced by L. perenne root tip in response to both elicitor and osmotic stress. Fructan epitopes were also detected in root cap cells and appeared to be released in the RET under stress conditions. Taken together our findings suggest that AGPs together with fructans are involved in root response of L. perenne to environmental stresses. • The root tip of perennial ryegrass produced border cells of different morphologies. • The root extracellular trap (RET) of perennial ryegrass contained abundant mucilage rich in arabinogalactan protein (AGP). • Fructan epitopes are released within the RET in response to PEG-induced osmotic stress and flagellin 22 elicitation. • Fructans, together with AGPs are promising candidates in root response to environmental stress in perennial ryegrass. [ABSTRACT FROM AUTHOR]