The atypical myrosinase PEN2 is required for broad-spectrum invasion resistance to filamentous plant pathogens. Previous localization studies suggested PEN2-GFP association with peroxisomes. Here we show that PEN2 is a tail-anchored protein with dual-membrane targeting to peroxisomes and mitochondria and that PEN2 has the capacity to form homo-oligomer complexes. We demonstrate pathogen-induced recruitment and immobilization of mitochondrial subpopulations at sites of attempted fungal invasion and show that mitochondrial arrest is accompanied by peripheral accumulation of GFP-tagged PEN2. PEN2 substrate production by the cytochrome P450 monooxygenase CYP81F2 is localized to the surface of the Endoplasmic Reticulum which focally reorganizes close to the immobilized mitochondria. Exclusive targeting of PEN2 to the outer membrane of mitochondria complements the pen2 mutant phenotype corroborating the functional importance of the mitochondrial PEN2 protein subpool for controlled local production of PEN2 hydrolysis products at subcellular plant-microbe interaction domains. Moreover, live cell imaging shows that mitochondria arrested at these domains exhibit a pathogen-induced redox imbalance which may lead to production of intracellular signals.

Non‐host resistance of Arabidopsis thaliana against Phytophthora infestans, the causal agent of late blight disease of potato, depends on efficient extracellular pre‐ and post‐invasive resistance responses. Pre‐invasive resistance against P. infestans requires the myrosinase PEN2. To identify additional genes involved in non‐host resistance to P. infestans, a genetic screen was performed by re‐mutagenesis of pen2 plants. Fourteen independent mutants were isolated that displayed an enhanced response to Phytophthora (erp) phenotype. Upon inoculation with P. infestans, two mutants, pen2‐1 erp1‐3 and pen2‐1 erp1‐4, showed an enhanced rate of mesophyll cell death and produced excessive callose deposits in the mesophyll cell layer. ERP1 encodes a phospholipid:sterol acyltransferase (PSAT1) that catalyzes the formation of sterol esters. Consistent with this, the tested T‐DNA insertion lines of PSAT1 are phenocopies of erp1 plants. Sterol ester levels are highly reduced in all erp1/psat1 mutants, whereas sterol glycoside levels are increased twofold. Excessive callose deposition occurred independently of PMR4/GSL5 activity, a known pathogen‐inducible callose synthase. A similar formation of aberrant callose deposits was triggered by the inoculation of erp1 psat1 plants with powdery mildew. These results suggest a role for sterol conjugates in cell non‐autonomous defense responses against invasive filamentous pathogens.

PCS1 is a moonlighting protein that functions in abiotic stress response and is indispensable for proper extracellular immune responses and pathogen-triggered g

The obligate biotrophic oomycete Plasmopara viticola causes tremendous problems in viticulture by evoking grapevine downy mildew. P. viticola, like other plant pathogens, achieves infection by suppression of plant innate immunity by secretion of effector molecules into its host plant. An ever-expanding family of proteins with effector-like characteristics is formed by the “Necrosis and Ethylene inducing peptide 1 (Nep1)-like proteins” (NLPs). NLPs can be divided into two groups by their ability to induce necrosis. While cytotoxic NLPs may act as virulence factors for a necrotrophic or hemibiotrophic plant pathogen, the role of non-cytotoxic NLPs is so far unknown. In this study, we identified eight independent NLPs in P. viticola and selected three for functional analysis. While one was identified as a putative pseudo gene, two contain all so far described critical key elements for necrosis formation except for an N-terminal signal peptide. Further characterization revealed that none of the putative necrosis elicitors was able to actually induce necrosis, neither in several susceptible or resistant Vitis species nor in the dicot model plant Nicotiana benthamiana. This inability exists independently of the presence or absence of a signal peptide. However, any possible mechanism for the suppression of the ability to induce necrosis in planta was not detected. Interestingly, expression analysis of the presumed pseudo gene revealed remarkable differences between pure sporangia solution and sporangia in the presence of leaf material. To our knowledge, this is the first report of this kind of regulation that suggests an important function of so far nonfunctional “pseudo” NLP genes during the first hours of infection.

Grapevine downy mildew is one of the major diseases in viticulture. To control this disease, a more effective strategy has been developed and established based on growth and model data as well as on a combination of fungicides. For this purpose, the systemic plant protection product potassium phosphonate (PP) was combined with two contact fungicides. Treatments were carried out according to the different experimental conditions after the growth of 400 cm², 600 cm², and 800 cm² leaf area per primary shoot. PP increased the effectiveness of the preventive fungicides whenever high infection pressure was the case. The experiments also show that it is possible to extend the treatment intervals from 400 cm² to 600 cm² new leaf area when PP was added. However, none of the tested treatments were sufficient for the extension to intervals of 800 cm². These data show that PP can be a key factor in the reduction of the application of synthetic or copper-based fungicides.

Grapevine Pinot gris virus (GPGV) was first identified in northern Italy in 2012 on grapevine variety Pinot gris showing chlorotic mottling and leaf deformation (1). Since 2012 GPGV has been reported from other countries including Slovenia, Slovakia, Czech Republic, Greece, France, Korea, United States, Canada and China. Since its discovery the association of a specific symptomology with the presence of GPGV has been contradictory. GPGV was often reported in mixed viral infections, making it difficult to associate GPGV with disease etiology. Moreover, the virus was also detected in asymptomatic vines. These observations suggest the existence of latent isolates and/or variable susceptibility of grapevine genotypes. The pathogenesis of GPGV remains unclear, therefore the studies of GPGV molecular variability and epidemiology are still of great importance. During a field survey conducted in 2015 in the state of Baden-Württemberg (Germany), symptoms resembling those caused by a viral infection (short internodes, zigzag growth of shoots, disturbed berry development) were observed in Vitis vinifera cv. Riesling vines in a commercial vineyard. Thirty vines were analyzed and were positive by RT-PCR using the GPGV- specific primer pair DetF/DetR (2). The RT-PCR amplicons from three vines were cloned and sequenced. The three amplicons were highly identical. Sequence analysis results revealed a 99% nucleotide sequence identity with the Slovak isolate SK30 of GPGV (GenBank accession number KF134123.1). Symptomatic leaves of these plants tested negative for Grapevine leafroll-associated viruses (GLRaV-1, -2, -3,- 4, and 7), Grapevine fanleaf virus, Raspberry ringspot virus, Grapevine fleck virus, Arabis mosaic virus, Strawberry latent ringspot, Tomato black ring virus, Tomato ringspot virus, Tobacco ringspot virus and Grapevine red blotch-associated virus by ELISA and/or PCR. In order to check the presence of other viral pathogens or undetected divergent viral variants, small interfering RNAs isolated from one symptomatic Riesling plant were analysed using Next Generation Sequencing (NGS) performed by the Illumina platform. Besides GPGV, this analysis identified three other infecting agents (Grapevine rupestris stem pitting-associated virus, Hop stunt viroid and Grapevine yellow speckle viroid 1). The full-length genome sequence of GPGV was obtained by combining the results of mapping of the Illumina reads on a reference GPGV genome, Sanger sequencing and RACE PCR. This genome sequence, showing 94-98% nt identity to complete genome sequences (KF686810, KF134124, KF134125, KM491305, NC _15782.1) was deposited in the GenBank database (GenBank accession number KX522755). To our knowledge, this is the first official report of GPGV in Germany.