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Suppression of PAMP-triggered immunity by coffee rust effectors may be attributed to their localization in the plant cell nucleus

Sérgio Brommonschenkel: Universidade Federal de Viçosa/Departamento de Fitopatologia

<div>Although studies have indicated that pathogen effectors may target a wide range of plant subcellular organelles in order to suppress host immunity, little is known about the function of effectors of rust fungi and their targets inside plant cells. Heterologous expression in <em>Nicotiana benthamiana</em> cells is an alternative approach to analyze <em>Hemileia vastatrix</em> candidate effectors (HvECs) due to the limited availability of molecular genetic tools to perform functional studies in this fungus. The present study aimed at performing a functional analysis of HvECs, through the evaluation of the ability of the candidate effectors to suppress PTI responses as well as by determining HvECs subcellular localization. Gene sequences encoding for 54 HvECs were individually cloned into pEDV6 vector (without signal peptide) and mobilized to <em>Pseudomonas fluorescens</em> EtHAn for transient expression in <em>N. benthamiana</em>. We found that 15 HvECs suppressed PTI with high reproducibility in different coinfiltration experiments with <em>Pseudomonas syringae</em> pv. <em>tomato</em> DC3000. We further designed a fluorescence-imaging-based screen to assess their subcellular localization. Confocal microscopy revealed that seven HvECs target the nucleus whereas only one effector accumulated in chloroplasts. <em></em>Coffee rust effectors may manipulate nuclear host immunity in order to suppress plant defense response and promote susceptibility.</div>