A LysM effector protein from the basidiomycete Rhizoctonia solani contributes to virulence through suppression of chitin-triggered immunity

Fredrik Dölfors,Louise Holmquist,Georgios Tzelepis,Christina Dixelius

doi:10.1007/s00438-019-01573-9

Fredrik Dölfors, Louise Holmquist + Show 2 more

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https://doi.org/10.1007/s00438-019-01573-9

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Abstract

Rhizoctonia solani is a fungal species that belongs to the fungal division Basidiomycota. It is a soil-borne pathogen that attacks a broad range of plant species and crops. Disease symptoms are commonly seen as damping off of seedlings and root rot, although it can infect plants at any developmental stage. Despite the severity of this disease, many aspects in R. solani infection biology remain unclear. Here we investigated the role of a LysM effector, previously predicted from the genome of a R. solani AG2-2IIIB strain that has sugar beet as a host. Gene expression analysis showed that RsLysM was highly induced upon sugar beet infection. When RsLysM was heterologously expressed in Cercospora beticola, necrotic lesion size and fungal colonization ability were increased, indicating a role in virulence. RsLysM displayed chitin-binding affinity and suppression of chitin-triggered immunity but could not protect hyphae from hydrolysis. Overall, this study is the first characterization of a LysM effector from Basidiomycota, suggesting that this necrotrophic fungal species relies on perturbation of chitin-triggered immunity to establish a successful infection.

Highlights

Rhizoctonia species are important soil-borne pathogens causing substantial yield losses in a wide range of crops including cereals, soybean, potato and sugar beet (Anderson 1982; Adams 1988)
No other domains were predicted, suggesting that the RsLysM has a modular structure similar to the already characterized homologs from filamentous ascomycetes. To test if this effector candidate is involved in virulence, we heterologously expressed it in the sugar beet hemibiotroph fungal pathogen C. beticola
Rhizoctonia solani is a fungus commonly described as a saprophyte, thriving on dead or dying plant debris/cells that is able to switch to a pathogenic endotrophic growth

Summary

Introduction

Rhizoctonia species (in Greek “root-killer”) are important soil-borne pathogens causing substantial yield losses in a wide range of crops including cereals, soybean, potato and sugar beet (Anderson 1982; Adams 1988). The sexual stage (Thanatephorus cucumeris) is extremely rare (Adams and Butler 1983) and conidia formation is lacking. This pathogen is classified into different anastomosis groups (AGs) based on hyphal cell wall fusion between different isolates. A general view is that R. solani hyphae adhere to the host plant surface and enter the outer cell layers by the formation of penetration cushions (Gonzalez et al 2011), a process followed by the growth of invasive hyphae that ramify through the host tissue. Genomic data are presently available from five different R. solani strains with cereal and dicot plant hosts (Zheng et al 2013; Cubeta et al 2014; Hane et al 2014; Wibberg et al 2013, 2016a, b), but hypotheses on

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