FoEG1, a secreted glycoside hydrolase family 12 protein from Fusariumoxysporum, triggers cell death and modulates plant immunity

Abstract

Fusarium oxysporum is an important soilborne fungal pathogen with many different formae speciales that can colonize the plant vascular system and cause serious crop wilt disease worldwide. We found a glycoside hydrolase family 12 protein FoEG1, secreted by F. oxysporum, that acted as a pathogen‐associated molecular pattern (PAMP) targeting the apoplast of plants to induce cell death. Purified FoEG1 protein triggered cell death in different plants and induced the plant defence response to enhance the disease resistance of plants. The ability of FoEG1 to induce cell death was mediated by leucine‐rich repeat (LRR) receptor‐like kinases BAK1 and SOBIR1, and this ability was independent of its hydrolase activity. The mutants of cysteine residues did not affect the ability of FoEG1 to induce cell death, and an 86 amino acid fragment from amino acid positions 144 to 229 of FoEG1 was sufficient to induce cell death in Nicotiana benthamiana. In addition, the expression of FoEG1 was strongly induced in the early stage of F. oxysporum infection of host plants, and FoEG1 deletion or loss of enzyme activity reduced the virulence of F. oxysporum. Therefore, our results suggest that FoEG1 can contribute to the virulence of F. oxysporum depending on its enzyme activity and can also act as a PAMP to induce plant defence responses.

Secreted Glycoside Hydrolase Proteins as Effectors and Invasion Patterns of Plant-Associated Fungi and Oomycetes

“…Another example of a secreted GH12 protein that is recognized as a MAMP by plants is FoEG1 from F. oxysporum ( Zhang et al, 2021d ). During infection of cotton and tomato roots, FoEG1 is most highly expressed during the early stages of infection, from 24 to 48 hpi ( Zhang et al, 2021d ). Deletion mutants (Δ foeg1 ) demonstrated reduced virulence on cotton plants ( Zhang et al, 2021d ).…”

“…During infection of cotton and tomato roots, FoEG1 is most highly expressed during the early stages of infection, from 24 to 48 hpi ( Zhang et al, 2021d ). Deletion mutants (Δ foeg1 ) demonstrated reduced virulence on cotton plants ( Zhang et al, 2021d ). This reduction in virulence was also observed for Δ foeg1 mutants complemented with a catalytically-inactivated version of the gene, indicating that the enzymatic activity of FoEG1 is required for full virulence of the pathogen ( Zhang et al, 2021d ).…”

The Role of Glycoside Hydrolases in Phytopathogenic Fungi and Oomycetes Virulence

“…FoEG1 is an apoplastic cell death-inducing protein, which is similar to VdEG1 from V. dahliae [20] and could be a PAMP to trigger plant cell death mediated by PRR-RLKs, BAK1, and SOBIR1 (Table 1). Thus, the results show that FoEG1 in F. oxysporum is an important virulence factor during infection and colonization by the fungus [51].…”

“…Recently, five proteins with GH12 domains have been found in the soil-borne vascular phytopathogenic fungus, F. oxysporum, among which, FoEG1 plays a crucial role in fungal pathogenicity as a virulence factor during interaction with its host [51]. FoEG1 is an apoplastic cell death-inducing protein, which is similar to VdEG1 from V. dahliae [20] and could be a PAMP to trigger plant cell death mediated by PRR-RLKs, BAK1, and SOBIR1 (Table 1).…”

Versatile effectors of phytopathogenic fungi target host immunity

“…In addition, SOBIR1 and BAK1 are required for V. dahliae VdEG1 and VdEG3 (GH12) to induce immunity in N. benthamiana , respectively, suggesting that both CWDEs may be recognized as pathogen‐associated molecular patterns (PAMPs) by different receptors (Gui et al, 2017). Generally, the cell death‐inducing CWDEs are categorized into two groups: one group of CWDEs including Fusarium oxysporium FoEG1 (GH12), B. cinerea xyloglucanase BcXYG1 (GH12) and xylanase BcXyl1 likely function as PAMPs to induce plant cell death, which is independent of their enzymatic activity (Zhu et al, 2017; Yang et al, 2018b; Zhang et al, 2021) (Figure 1); and another group including the putative endo‐β‐1,3 glucanases CfGH17‐1 and CfGH17‐5 in the biotrophic pathogen C. fulvum induce cell death, which is dependent of their enzymatic activity, suggesting that the cell wall products released by these CWDEs are recognized as danger‐associated molecular patterns (DAMPs) (Ökmen et al, 2019). In addition, multiple putative apoplastic effectors in the biotrophic Ustilaginoidea virens and hemibiotrophic M. oryzae induce cell death in plants (Chen et al, 2013; Fang et al, 2016).…”