The RsRlpA Effector Is a Protease Inhibitor Promoting Rhizoctonia solani Virulence through Suppression of the Hypersensitive Response

Abstract

Rhizoctonia solani (Rs) is a soil-borne pathogen with a broad host range. This pathogen incites a wide range of disease symptoms. Knowledge regarding its infection process is fragmented, a typical feature for basidiomycetes. In this study, we aimed at identifying potential fungal effectors and their function. From a group of 11 predicted single gene effectors, a rare lipoprotein A (RsRlpA), from a strain attacking sugar beet was analyzed. The RsRlpA gene was highly induced upon early-stage infection of sugar beet seedlings, and heterologous expression in Cercospora beticola demonstrated involvement in virulence. It was also able to suppress the hypersensitive response (HR) induced by the Avr4/Cf4 complex in transgenic Nicotiana benthamiana plants and functioned as an active protease inhibitor able to suppress Reactive Oxygen Species (ROS) burst. This effector contains a double-psi beta-barrel (DPBB) fold domain, and a conserved serine at position 120 in the DPBB fold domain was found to be crucial for HR suppression. Overall, R. solani seems to be capable of inducing an initial biotrophic stage upon infection, suppressing basal immune responses, followed by a switch to necrotrophic growth. However, regulatory mechanisms between the different lifestyles are still unknown.

Unveiling the Core Effector Proteins of Oil Palm Pathogen Ganoderma boninense via Pan-Secretome Analysis

“…Besides that, several differentially expressed CEP genes were also linked to the modulation of HR. The downregulated CEP genes encoding the papain inhibitor and guanyl-specific ribonuclease were suggested to suppress HR by inhibiting the protease involved in HR induction and binding to the host’s ribosome-inactivating proteins, respectively [ 85 , 86 ] ( Supplementary Table S7 ). This was also coupled with the upregulation of the cell death-associated NLP-class CEP that was previously reported in G. boninense [ 14 , 15 ].…”

Effectors of Plant Necrotrophic Fungi

“…VdPDA1 is highly expressed early in infection and likely contributes to a successful biotrophic phase of V. dahlia infection, as PDA1 knockout mutants had severely reduced virulence (Gao et al, 2019). Another R. solani AG2-2IIIB effector protein, RsRlpA, encodes a rare lipoprotein A-like that has immunity suppressing activity (Charova et al, 2020). RsRlpA is highly induced during early infection of sugar beets, and its overexpression in N. benthamiana suppresses HR imposed by C. fulvum Avr4 (Charova et al, 2020).…”

“…Another R. solani AG2-2IIIB effector protein, RsRlpA, encodes a rare lipoprotein A-like that has immunity suppressing activity (Charova et al, 2020). RsRlpA is highly induced during early infection of sugar beets, and its overexpression in N. benthamiana suppresses HR imposed by C. fulvum Avr4 (Charova et al, 2020). RsRlpA shares sequence homology to papain-like inhibitors which are known for blocking activity of papain-like cysteine proteases (PL) that help induce PCD and other immune responses in plants (reviewed by Misas-Villamil et al, 2016).…”

Unveiling the Core Effector Proteins of Oil Palm Pathogen <i>Ganoderma boninense</i> via Pan-secretome Analysis

“…Besides that, several differentially expressed CEP genes were also linked to the modulation of HR. The downregulated CEP genes encoding papain inhibitor and guanyl-specific ribonuclease were suggested to suppress HR by inhibiting the protease involved in HR induction and binding to the host ribosome-inactivating proteins, respectively [84,85] (Supplementary Table 7). This is also coupled with the upregulation of cell death-associated NLP-class CEP that was previously reported in G. boninense [14,15].…”