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

Abstract

The induction of plant defense‐related responses by chitin oligomers and the Rhizobium meliloti lipo‐chito‐oligosaccharide nodulation signals (Nod factors) in Medicago 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 R. meliloti 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 Medicago microcallus cultures revealed differences between cells treated with N‐acetyl‐chitotetraose and those treated with Nod factor and demonstrated increased production of the phytoalexin medicarpin in the presence of Nod factor. In Medicago roots, none of the tested genes was activated by the N‐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 Medicago cells possess distinct perception systems for these related molecules.

The Root Hair “Infectome” of Medicago truncatula Uncovers Changes in Cell Cycle Genes and Reveals a Requirement for Auxin Signaling in Rhizobial Infection

“…In contrast, Nod factor and S. meliloti increased expression of VRC2 (encoding the second last step in the biosynthesis of the phytoalexin medicarpin) specifically at the sites of infection. This indicates that M. truncatula may produce antimicrobials in during infection and is consistent with the detection of medicarpin during nodulation (Savouré et al, 1997). This could limit opportunistic and/or pathogenic infections (Pandya et al, 2013).…”

“…Medicarpin is produced during nodulation and is induced by Nod factors and rhizobia (Dakora et al, 1993;Phillips et al, 1994;Savouré et al, 1997). S. meliloti also induced isoflavone 2'-hydroxylase (IF2'H), isoflavone reductase (IFR), and two vestitone reductases (VR), which catalyze the penultimate step of the pathway for medicarpin biosynthesis.…”

Molecular Basis of Symbiotic Promiscuity

“…Nevertheless, expression of a chitinase from Serratia marcescens by R. fredii USDA191 transconjugants resulted in delayed nodulation and a marked decrease in total nodule number on soybean cultivar McCall in comparison with the wild-type strain (146). What is undisputed, however, is that chitinases modulate the levels of Nod factors in the rhizosphere and, in so doing, help suppress defense responses stimulated by high concentrations of LCOs (231,260). Since defense reactions also occur in aborted infection threads (273), it is possible that plant hydrolases help regulate Nod factor levels even after the bacterium has entered the plant.…”

Sinorhizobium meliloti nifA mutant induces different gene expression profile from wild type in Alfalfa nodules

“…PAL catalyses the non-oxidative deamination of l-phenylalanine to trans-cinnamic acid. This enzyme is ubiquitous in plants and is involved in the production of phenylpropanoids such as lignin and phytoalexins [50,51]. The amino-acid permease (G37) is an integral membrane protein involved in the transport of amino acids into the cell.…”