Lipo‐chitooligosaccharide signalling blocks a rapid pathogen‐induced ROS burst without impeding immunity

Abstract

Summary Molecular signals released by microbes at the surface of plant roots and leaves largely determine host responses, notably by triggering either immunity or symbiosis. How these signalling pathways cross‐talk upon coincident perception of pathogens and symbionts is poorly described in plants forming symbiosis. Nitrogen fixing symbiotic Rhizobia spp. and arbuscular mycorrhizal fungi produce lipo‐chitooligosaccharides (LCOs) to initiate host symbiotic programmes. In Medicago truncatula roots, the perception of LCOs leads to reduced efflux of reactive oxygen species (ROS). By contrast, pathogen perception generally triggers a strong ROS burst and activates defence gene expression. Here we show that incubation of M. truncatula seedlings with culture filtrate (CF) of the legume pathogen Aphanomyces euteiches alone or simultaneously with Sinorhizobium meliloti LCOs, resulted in a strong ROS release. However, this response was completely inhibited if CF was added after pre‐incubation of seedlings with LCOs. By contrast, expression of immunity‐associated genes in response to CF and disease resistance to A. euteiches remained unaffected by LCO treatment of M. truncatula roots. Our findings suggest that symbiotic plants evolved ROS inhibition response to LCOs to facilitate early steps of symbiosis whilst maintaining a parallel defence mechanisms toward pathogens.

A combination of chitooligosaccharide and lipochitooligosaccharide recognition promotes arbuscular mycorrhizal associations in Medicago truncatula

“…5c), a PR10 and a chitinase, revealed that co-treatment with Sm LCO inhibited CO8 induction of these genes (Fig. 5c), in disagreement with a recent report 56 . The combination of LCOs and COs inhibits defense-related gene expression, but these two signals act synergistically to enhance the degree of symbiotic gene expression, as measured using qRT-PCR of Vapyrin and HA1 (Fig.…”

Distinct genetic basis for root responses to lipo-chitooligosaccharide signal molecules from different microbial origins

“…Possibly linked to their roles as symbiotic signals, LCOs can interfere with immunity-related signaling in legumes (Rey et al, 2019) and suppress innate immune responses, even in the nonmycorrhizal plant Arabidopsis thaliana (Liang et al, 2013). How LCOs dampen legume immunity is still unclear as they can also induce defense gene expression (Nakagawa et al, 2011).…”

Liana T. Burghardt

“…Cu, Fe) to rhizobia housed in symbiosomes and thus influence N‐fixation (Senovilla et al , 2018; Lui et al , 2020). Similarly, recent papers highlight the complex crosstalk between legume immunity and rhizobial symbiosis (Berrabah et al , 2018; Rey et al , 2019; Sorroche et al , 2019).…”