The Irish Potato Famine Pathogen Phytophthora infestans Translocates the CRN8 Kinase into Host Plant Cells

Mireille Van Damme,Alexandra M E Jones,Sebastian Schornack,Sophien Kamoun,Cahid Cakir,Tolga O Bozkurt,Jan Sklenar,Barbara J Howlett

doi:10.1371/journal.ppat.1002875

Abstract

Phytopathogenic oomycetes, such as Phytophthora infestans, secrete an arsenal of effector proteins that modulate plant innate immunity to enable infection. We describe CRN8, a host-translocated effector of P. infestans that has kinase activity in planta. CRN8 is a modular protein of the CRN effector family. The C-terminus of CRN8 localizes to the host nucleus and triggers cell death when the protein is expressed in planta. Cell death induction by CRN8 is dependent on its localization to the plant nucleus, which requires a functional nuclear localization signal (NLS). The C-terminal sequence of CRN8 has similarity to a serine/threonine RD kinase domain. We demonstrated that CRN8 is a functional RD kinase and that its auto-phosphorylation is dependent on an intact catalytic site. Co-immunoprecipitation experiments revealed that CRN8 forms a dimer or multimer. Heterologous expression of CRN8 in planta resulted in enhanced virulence by P. infestans. In contrast, in planta expression of the dominant-negative CRN8R469A;D470A resulted in reduced P. infestans infection, further implicating CRN8 in virulence. Overall, our results indicate that similar to animal parasites, plant pathogens also translocate biochemically active kinase effectors inside host cells.

Highlights

Phytopathogenic oomycetes, such as Phytophthora spp., cause some of the most destructive plant diseases in the world [1]
The P. ramorum CRN8 paralog sequences share only 33% amino acid identity to CRN8 compared to 97–99% identity among the P. infestans kinase domains (Figure S1)
In this study, we functionally characterize the CRN8 effector, a secreted kinase from P. infestans previously shown to be delivered into plant cells via its N-terminal targeting motif [42]

Summary

Introduction

Phytopathogenic oomycetes, such as Phytophthora spp., cause some of the most destructive plant diseases in the world [1]. Phytophthora spp. are hemibiotrophic pathogens, meaning that they have a two-step infection process: an early biotrophic phase (the first 2–3 days after infection), followed by a second phase characterized by extensive host tissue necrosis which enables additional growth and sporulation of the pathogen [2]. To achieve this level of host colonization, plant and animal pathogens secrete molecules, termed effectors, that interfere with host immune pathways and enable host colonization [3,4,5]. Elucidating the molecular mechanisms underlying effector activity remains challenging and is dependent on identifying host targets of these effectors [10,11]

Methods

Results

Conclusion