A Putative Effector CcSp84 of Cytospora chrysosperma Localizes to the Plant Nucleus to Trigger Plant Immunity

Abstract

Cytospora chrysosperma is the main causal agent of poplar canker disease in China, especially in some areas with poor site conditions. Pathogens secrete a large number of effectors to interfere the plant immunity and promote their infection and colonization. Nevertheless, the roles of effectors in C. chrysosperma remain poorly understood. In this study, we identified and functionally characterized a candidate effector CcSp84 from C. chrysosperma, which contained a nuclear localization signal motif at the C-terminal and was highly induced during infection stages. Transient expression of CcSp84 in Nicotiana benthamiana leaves could trigger cell death. Additionally, deletion of CcSp84 significantly reduced fungal virulence to the polar twigs, while no obvious defects were observed in fungal growth and sensitivity to H2O2. Confocal microscopy revealed that CcSp84 labeled with a green fluorescent protein (GFP) was mainly accumulated in the plant nucleus. Further analysis revealed that the plant nucleus localization of CcSp84 was necessary to trigger plant immune responses, including ROS accumulation, callose deposition, and induced expression of jasmonic acid and ethylene defense-related genes. Collectively, our results suggest that CcSp84 is a virulence-related effector, and plant nucleus localization is required for its functions.

The mitogen-activated protein kinase module CcSte11-CcSte7-CcPmk1 regulates pathogenicity via the transcription factor CcSte12 in Cytospora chrysosperma

“…XEG1 from Phytophthora sojae , which exhibits xyloglucanase activity and promotes infection by degrading plant cell walls (Ma et al 2015 ). Additionally, GME8128_g , a GH61 family gene, has been characterized in C. chrysosperma and was named CcSp84 , which was essential for fungal pathogenicity (Xu et al 2022 ). Importantly, CcSp84 contains the element TGAAACA in its promoter, which is a sequence interaction with the Ste12 protein in S. cerevisiae (Yuan and Fields 1991 ).…”

“…In addition, FoEG1 contributes to the pathogenicity of F. oxysporum as well. Moreover, CcSp84 was critical for fungal pathogenicity and could also induce cell death and immune responses in N. benthamiana (Xu et al 2022 ). And the plant nucleus localization of CcSp84 was essential to trigger the plant defense responses (Xu et al 2022 ).…”

“…Moreover, CcSp84 was critical for fungal pathogenicity and could also induce cell death and immune responses in N. benthamiana (Xu et al 2022 ). And the plant nucleus localization of CcSp84 was essential to trigger the plant defense responses (Xu et al 2022 ). Importantly, CcSp84 contain the element TGAAACA in its promoter and CcSte12 interacts with the CcSp84 -promoter.…”