An unbiased nuclear proteomics approach reveals novel nuclear protein components that participates in MAMP-triggered immunity

ABSTRACT: (MAMP)-triggered immunity (MTI) is the first layer of molecular defense encountered by pathogens. Genetic screens have contributed to our knowledge of MTI, but are limited to phenotype-causing mutations. Here we attempt to identify novel factors involved in the early event leading to plant MTI by comparing the nuclear proteomes of two Arabidopsis genotypes treated with chitosan. Our approach revealed that following chitosan treatment, cerk1 plants had many nuclear accumulating proteins in common, but also some unique ones, when compared with Col-0 plants. Analysis of the identified proteins revealed a nuclear accumulation of DNA-modifying enzymes, RNA-binding proteins and ribosomal proteins. Our results demonstrate that nuclear proteomic is a valid, phenotype-independent approach to uncover factor involved in cellular processes. © 2016 The Author(s). Published with license by Taylor & Francis

Infection assays in Arabidopsis reveal candidate effectors from the poplar rust fungus that promote susceptibility to bacteria and oomycete pathogens

Fungi of the Pucciniales order cause rust diseases which, altogether, affect thousands of plant species worldwide and pose a major threat to several crops. How rust effectors—virulence proteins delivered into infected tissues to modulate host functions— contribute to pathogen virulence remains poorly understood. Melampsora larici-populina is a devastating and widespread rust pathogen of poplar, and its genome encodes 1184 identified small secreted proteins that could potentially act as effectors. Here, following specific criteria, we selected 16 candidate effector proteins and characterized their virulence activities and subcellular localizations in the leaf cells of Arabidopsis thaliana. Infection assays using bacterial (Pseudomonas syringae) and oomycete (Hyaloperonospora arabidopsidis) pathogens revealed subsets of candidate effectors that enhanced or decreased pathogen leaf colonization. Confocal imaging of green fluorescent protein-tagged candidate effectors constitutively expressed in stable transgenic plants revealed that some protein fusions specifically accumulate in nuclei, chloroplasts, plasmodesmata and punctate cytosolic structures. Altogether, our analysis suggests that rust fungal candidate effectors target distinct cellular components in host cells to promote parasitic growth. © 2016 BSPP AND JOHN WILEY & SONS LTD

The 124202 candidate effector of <i>Melampsora larici-populina</i> interacts with membranes in <i>Nicotiana</i> and <i>Arabidopsis</i>

<p><i>Melampsora larici-populina</i> (<i>Mlp</i>) is a parasitic fungus causing poplar leaf rust, a disease that threatens poplar plantations worldwide. Like other phytopathogens, <i>Mlp</i> translocates specialized proteins, called effectors, into host tissues and cells to eventually divert host resources. 124202 is a hypothetical <i>Mlp</i> effector selected through an <i>in silico</i> secretome analysis. It shares about 30% identity with the <i>M. lini</i> AvrM effector. Using heterologous systems, the objectives of this work were to assess if 124202 could mitigate <i>Arabidopsis</i> defence or potentiate <i>Pseudomonas</i> virulence and investigate its putative interaction partners in plants. Yeast two-hybrid screens identified three potential 124202 interactors in plants: lipoxygenase 2, synaptotagmin A and quinolinate synthase. Expression of a fluorescently tagged 124202 protein in <i>Nicotiana benthamiana</i> and <i>Arabidopsis thaliana</i> showed that it could be associated with membranes but may also be found in the cytoplasm of host cells. Bacterial infection assays in wild-type and 124202-expressing <i>Arabidopsis</i> lines indicate that 124202 does not alter the susceptibility of <i>Arabidopsis</i> to <i>Pseudomonas syringae</i> pv. <i>tomato</i> DC3000. Overall, our results suggest that the function of 124202 might involve vesicle-mediated trafficking but is unlikely to quantifiably contribute to the suppression of plant immunity.</p