Distinct response of <i>Medicago</i> suspension cultures and roots to Nod factors and chitin oligomers in the elicitation of defense‐related responses

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<jats:p>The induction of plant defense‐related responses by chitin oligomers and the <jats:italic>Rhizobium meliloti</jats:italic> lipo‐chito‐oligosaccharide nodulation signals (Nod factors) in <jats:italic>Medicago</jats:italic> cell cultures and roots was investigated by following the expression of genes encoding enzymes of the isoflavonoid biosynthetic pathway, such as chalcone synthase, chalcone reductase, isoflavone reductase, as well as genes encoding a pathogenesis‐related protein and a peroxidase. In suspension‐cultured cells, all genes except the peroxidase gene were induced by both the <jats:italic>R. meliloti</jats:italic> Nod factor NodRm‐IV(C16:2,S) and chitin oligomers with a minimum of three sugar residues. However, activation of these genes was not elicited by the symbiotically inactive, desulfated NodRm‐IV(C16:2). Moreover, the cells were more sensitive to the chitin oligosaccharides than to the Nod factor. Analysis of flavonoids in <jats:italic>Medicago</jats:italic> microcallus cultures revealed differences between cells treated with <jats:italic>N</jats:italic>‐acetyl‐chitotetraose and those treated with Nod factor and demonstrated increased production of the phytoalexin medicarpin in the presence of Nod factor. In <jats:italic>Medicago</jats:italic> roots, none of the tested genes was activated by the <jats:italic>N</jats:italic>‐acetylchitotetraose, whereas the Nod factor at micro‐molar concentration enhanced transient expression of the isoflavonoid biosynthetic genes. The differential responses to Nod factors and chitin oligomers suggest that <jats:italic>Medicago</jats:italic> cells possess distinct perception systems for these related molecules.</jats:p>

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