Egg box conformation of oligogalacturonides: The time-dependent stabilization of the elicitor-active conformation increases its biological activity

Abstract

Circular dichroism spectrometry was used on oligogalacturonides (OGAs) and showed the existence of a calcium/sodium-induced conformational state that is intermediate between single-isolated chains and calcium-associated multimer chains. This conformation is interpreted as being egg box dimers. Using the 2F4 monoclonal antibody that specifically binds such an egg box dimer conformation of pectin, the stability of OGA dimers was investigated over a period of 24 hours. The extent to which egg box dimers were recognized by the antibody was dependent on the temperature and duration of preincubation of the OGA. This suggests a "maturation" process of the egg-box structure that consists in a progressive increase in the length of the junction sequences between two chains that slide along each other in order to form a maximum number of calcium bridges and dimer ends. The maturation of egg boxes induced both a significant increase in their binding to wall-associated kinase 1 (WAK1) and an increased extracellular alkalinization when applied to Arabidopsis thaliana cell suspensions. The chemical modification of the reducing end of the OGAs largely diminished their elicitating activity but did not hinder either dimerization or binding of these end-reduced egg boxes to WAK1. We conclude that there are at least two different perception systems for egg box dimers. One binds egg box junctions and the other binds egg box ends. The relevance of these results is discussed in terms of pectic signal perception and plant-pathogen interaction.

Arabidopsis PECTIN METHYLESTERASEs Contribute to Immunity against Pseudomonas syringae

“…Degradation of pectin by pectin-degrading enzymes requires a certain level of pectin deesterification. Pectin fragments with a low degree of esterification and a size between 10 and 15 GalA residues show the highest elicitor activity (Cabrera et al, 2008;Ferrari et al, 2013). Perhaps increased PME activity triggers the production of OGs with more elicitor activity, resulting in increased induction of defense responses.…”

“…Moreover, in wheat (Triticum aestivum) near-isogenic lines, a blockwise distribution of methylesters was detected in lines susceptible to Puccinia graminis compared with a more random distribution in resistant lines (Wiethölter et al, 2003). In addition, the elicitor activity of OGs is dependent on the degree and distribution of methylesters (Cabrera et al, 2008;Osorio et al, 2008). Thus, it is likely that patterns of methylesterification affect plant-pathogen interactions.…”

“…Recognition of OGs activates downstream defense responses including reactive oxygen species production, ethylene production, and callose deposition (Ferrari et al, 2013). Deesterified OGs show increased elicitor activity and binding to WAK1 when in the egg-box conformation (Cabrera et al, 2008).…”

Plant Cell Wall Polymers: Function, Structure and Biological Activity of Their Derivatives

“…The increase in cytosolic free Ca 2+ has been proposed to mediate the regulation of stomatal aperture and production of hydrogen peroxide in the guard cells of tomato (Licopersicon esculentum L.) and Commelina communis L. [55]. Calcium may also directly interact with long-sized OGAs promoting the formation of structures with an "egg-box" conformation, which may potentiate their biological activity [56]. Nevertheless the promotion of vegetative shoot formation in Nicotiana tabacum explants has been observed to be independent of exogenous Ca 2+ [57].…”

A domain swap approach reveals a role of the plant wall-associated kinase 1 (WAK1) as a receptor of oligogalacturonides

“…Like hyaluronan fragments, OGs are regarded as host-or damage-associated molecular patterns (HAMPs or DAMPs) and their biological activity is related to their molecular size because OGs with a degree of polymerization (DP) between 10 and 15 are the most active (13,14). Notably, the "egg box" conformation is necessary for the biological activity of OGs (5,15).…”