Lipochitooligosaccharide recognition: an ancient story

Abstract

SummaryChitin is the second most abundant polysaccharide in nature, found in crustacean shells, insect exoskeletons and fungal cell walls. The action of chitin and chitin derivatives on plants has become a very interesting story of late. Chitin is a b1-4-linked polymer of N-acetyl-Dglucosamine (GlcNAc). In this unmodified form, chitooligosaccharides (degree of polymerization (dp) = 6-8)) are strong inducers of plant innate immunity. By contrast, when these chitooligosaccharides are acylated (so-called lipochitooligosaccharides, LCOs) and further modified, they can act as Nod factors, the key signaling molecules that play an important role in the initiation of the legume-rhizobium symbiosis. In a similar form, these molecules can also act as Myc factors, the key signaling molecules involved in the arbuscular mycorrhizal (AM) symbiosis. It has been proposed that Nod factor perception might have evolved from the more ancient AM symbiosis. Increasing evidence now suggests that LCO perception might have evolved from plant innate immunity signaling. In this review, we will discuss the evolutionary origin of symbiotic LCO recognition.

Rhizobium–legume symbiosis in the absence of Nod factors: two possible scenarios with or without the T3SS

“…It is therefore tempting to speculate that the triggering of the symbiotic program involves a direct contact between the plant and the bacterium, probably through the perception of a bacterial surface component by a plant receptor. Increasing evidence now suggests that NFs perception might have evolved from plant innate immunity signaling and the possibility has been evocated that the first function of Nod factors was to suppress defense reaction (Liang et al, 2014). The presented results that non-photosynthetic bradyrhizobia can interact symbiotically in the absence of NFs but through a T3SS which is also known to interfere with the plant immunity reinforces the hypothesis that the suppression of the MAMP-triggered immunity constituted the first evolutionary step towards symbiosis.…”

A micromolar concentration of lipo-chitooligosaccharide (Nod Bj V [C18:1, MeFuc]) regulates the emergence and seed productivity of rapid cycling canola (Brassica napus [L.]) plants

“…LCOs may represent a novel class of plant growth regulator involved in plant developmental processes. In a smaller brassicaceous plant, which is often used as a model of B. napus, Arabidopsis, lysin motif (LysM) proteins have been shown to bind GlcNAc residues as demonstrated by their precipitation using chitin beads (Liang et al 2014). LysM domains associated with a receptor-like kinase (RLK) domain form a LysM-RLK, termed CERK1 or LysM-RLK1 (Liang et al 2014).…”

“…In a smaller brassicaceous plant, which is often used as a model of B. napus, Arabidopsis, lysin motif (LysM) proteins have been shown to bind GlcNAc residues as demonstrated by their precipitation using chitin beads (Liang et al 2014). LysM domains associated with a receptor-like kinase (RLK) domain form a LysM-RLK, termed CERK1 or LysM-RLK1 (Liang et al 2014). Recently published work indicates that Arabidopsis responded to chitin signals by the induction of immune responses at the micromolar range, but suppressed immune responses at the nanomolar range (Liang et al 2014).…”

“…LysM domains associated with a receptor-like kinase (RLK) domain form a LysM-RLK, termed CERK1 or LysM-RLK1 (Liang et al 2014). Recently published work indicates that Arabidopsis responded to chitin signals by the induction of immune responses at the micromolar range, but suppressed immune responses at the nanomolar range (Liang et al 2014).…”

“…LysM domains associated with a receptor-like kinase (RLK) domain form a LysM-RLK, termed CERK1 or LysM-RLK1 (Liang et al 2014). Recently published work indicates that Arabidopsis responded to chitin signals by the induction of immune responses at the micromolar range, but suppressed immune responses at the nanomolar range (Liang et al 2014).Treatment with LCO can increase abscisic acid (10.19 %) and salicylic acid (15.00 %), and decrease indolylacetic acid (¡49.68 %), cytokinin (¡36.24 %), gibberellic acid (¡19.41 %), and jasmonic acid (¡33.66 %) total content of Arabidopsis rosettes, 24 h post treatment (Subramanian 2014). These levels of salicylic acid accumulation are somewhat less than the 100 to 200 % increase over background levels that would be expected to be induced at the primary leaf due to second stage systemic acquired resistance (SAR).…”