The oomycete Aphanomyces euteiches is a root pathogen infecting legumes which causes important yield losses. The cell wall of A.euteiches contains 10% N-acetylglucosamine (NAG) in the form of non-crystalline chitosaccharides, which are associated to cell wall glucans. To study their biological activity, a root elicitation bioassay on the host plant Medicago truncatula has been set up using a preparation of chitin fragments as a control elicitor. The purification of hydrolysed cell wall fractions enriched in NAG yielded glycan fragments which were composed of glucose and NAG. These heteropolymers possess a novel structure, which has never been described before. The root elicitation bioassay showed a biological activity of the cell wall fractions different from the one of chitin fragments, on M.truncatula. Interestingly, one fraction induced nuclear calcium oscillations in epidermal cells of M.truncatula root cultures, which are different from the response evoked by pure chitotetramers.
Structural characterization and perception by the host plant Medicago truncatula of the cell wall chitosaccharides of the legume parasite Aphanomyces euteiches.