Nonhost Resistance of Arabidopsis thaliana Against Alternaria alternata Involves both Pre- and Postinvasive Defenses but Is Collapsed by AAL-Toxin in the Absence of LOH2

The tomato pathotype of Alternaria alternata causes Alternaria stem canker on tomato depending upon the production of the host-specific AAL-toxin. Host defense mechanisms to A. alternata, however, are largely unknown. Here, we elucidate some of the mechanisms of nonhost resistance to A. alternata using Arabidopsis mutants. Wild-type Arabidopsis showed either no symptoms or a hypersensitive reaction (HR) when inoculated with both strains of AAL-toxin-producing and non-producing A. alternata. Yet, when these Arabidopsis penetration (pen) mutants, pen2 and pen3, were challenged with both strains of A. alternata, fungal penetration was possible. However, further fungal development and conidiation were limited on these pen mutants by postinvasion defense with HR-like cell death. Meanwhile, only AAL-toxin-producing A. alternata could invade lag one homologue (loh)2 mutants, which have a defect in the AAL-toxin resistance gene, subsequently allowing the fungus to complete its life cycle. Thus, the nonhost resistance of Arabidopsis thaliana to A. alternata consists of multilayered defense systems that include pre-invasion resistance via PEN2 and PEN3 and postinvasion resistance. However, our study also indicates that the pathogen is able to completely overcome the multilayered nonhost resistance if the plant is sensitive to the AAL-toxin, which is an effector of the toxin-dependent necrotrophic pathogen A. alternata.

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Sphingosine-related mycotoxins in plant and animal diseases

Canadian Journal of Botany ◽

10.1139/b95-283 ◽

1995 ◽

Vol 73 (S1) ◽

pp. 459-467 ◽

Cited By ~ 33

Author(s):

David G. Gilchrist ◽

Richard M. Bostock ◽

Hong Wang

Keyword(s):

Cell Death ◽

Alternaria Alternata ◽

Fusarium Moniliforme ◽

Cellular Response ◽

Stem Canker ◽

Ceramide Synthase ◽

Sucrose Transport ◽

Aal Toxin ◽

Aal Toxins ◽

Alternaria Stem Canker

The AAL-toxins and fumonisins are a group of chemically related phytotoxic congeners produced by Alternaria alternata f. sp. lycopersici and Fusarium moniliforme, respectively, that also are widespread mycotoxins with important health implications. These mycotoxins, which bear a structural relationship to the sphingoid base, sphingosine, also incite maladies in animals ranging from neoplasms to renal, neural, and hepatic necrosis. A. alternata f. sp. lycopersici causes the Alternaria stem canker disease in tomatoes, while F. moniliforme causes pink ear rot of maize and is associated with post-harvest contamination of many different food staples. These toxins are potent inhibitors of ceramide synthase in plants and animals. Sphingoid bases are mediators of signal transduction leading to neoplasms and necrosis in animals. Significant inhibition of ceramide synthase in microsomal preparations of tomato occurs at 20 nM with an I50 in the range of 35–40 nM for both AAL-toxin, TA, and fumonisin, FB1. In plants, specific alterations of physiological processes associated with cellular response to these toxins appears to be required for cell death. A net decrease in sucrose influx to treated leaves occurs within 4 h of AAL-toxin treatment. Untreated leaves of toxin-resistant and -sensitive isolines of tomato show significant differences in sucrose transport capacity. Exogenous application of sucrose transport inhibitors mimicked AAL-toxin symptoms and enhanced cell death in susceptible lines of tomato. Conversely, the accumulation of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACQ occurred in 1 h and increased rapidly during the next 6 h after exposure to AAL-toxin. ACC accumulation is followed by a burst in ethylene within 12 h. Application of specific inhibitors of ethylene synthesis or ethylene action results in a decrease in toxin-induced cell death. These toxins appear to be useful tools for defining biochemical and molecular features common to induced cell death in both plants and animals. Key words: AAL-toxins, fumonisins, mycotoxins, host-selective toxins, Alternaria stem canker, Alternaria alternata, Fusarium moniliforme.

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AAL-Toxin-Deficient Mutants of Alternaria alternata Tomato Pathotype by Restriction Enzyme-Mediated Integration

Phytopathology ◽

10.1094/phyto.1997.87.9.967 ◽

1997 ◽

Vol 87 (9) ◽

pp. 967-972 ◽

Cited By ~ 97

Author(s):

H. Akamatsu ◽

Y. Itoh ◽

M. Kodama ◽

H. Otani ◽

K. Kohmoto

Keyword(s):

Restriction Enzyme ◽

Alternaria Alternata ◽

Restriction Enzymes ◽

Toxin Production ◽

Molecular Genetic Analysis ◽

Transformation Frequency ◽

Fungal Genome ◽

Plasmid Integration ◽

Tomato Pathotype ◽

Aal Toxin

Host-specific toxins are produced by three pathotypes of Alternaria alternata: AM-toxin, which affects apple; AK-toxin, which affects Japanese pear; and AAL-toxin, which affects tomato. Each toxin has a role in pathogenesis. To facilitate molecular genetic analysis of toxin production, isolation of toxin-deficient mutants utilizing ectopic integration of plasmid DNA has been attempted. However, the transformation frequency was low, and integration events in most transformants were complicated. Addition of a restriction enzyme during transformation has been reported to increase transformation frequencies significantly and results in simple plasmid integration events. We have, therefore, optimized this technique, known as restriction enzyme-mediated integration (REMI), for A. alternata pathotypes. Plasmid pAN7-1, conferring resistance to hygromycin B, with no detectable homology to the fungal genome was used as the transforming DNA. Among the three restriction enzymes examined, HindIII was most effective, as it increased transformation frequency two-to 10-fold depending on the pathotype, facilitating generation of several hundred transformants with a 1-day protocol. BamHI and XbaI had no significant effect on transformation frequencies in A. alternata pathotypes. Furthermore, the transforming plasmid tended to integrate as a single copy at single sites in the genome, compared with trials without addition of enzyme. Libraries of plasmid-tagged transformants obtained with and without addition of restriction enzyme were constructed for the tomato pathotype of A. alternata and were screened for toxin production. Three AAL-toxin-deficient mutants were isolated from a library of transformants obtained with addition of enzyme. These mutants did not cause symptoms on susceptible tomato, indicating that the toxin is required for pathogenicity of the fungus. Characterization of the plasmid integration sites and rescue of flanking sequences are in progress.

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Mutations Found in the Asc1 Gene That Confer Susceptibility to the AAL-Toxin in Ancestral Tomatoes from Peru and Mexico

Plants ◽

10.3390/plants10010047 ◽

2020 ◽

Vol 10 (1) ◽

pp. 47

Author(s):

Rin Tsuzuki ◽

Rosa María Cabrera Pintado ◽

Jorge Andrés Biondi Thorndike ◽

Dina Lida Gutiérrez Reynoso ◽

Carlos Alberto Amasifuen Guerra ◽

...

Keyword(s):

Phylogenetic Tree ◽

Solanum Lycopersicum ◽

Alternaria Alternata ◽

Stem Canker ◽

Pathogenic Factor ◽

Canker Disease ◽

Nucleotide Deletion ◽

History Of ◽

Aal Toxin

Tomato susceptibility/resistance to stem canker disease caused by Alternaria alternata f. sp. lycopersici and its pathogenic factor AAL-toxin is determined by the presence of the Asc1 gene. Several cultivars of commercial tomato (Solanum lycopersicum var. lycopersicum, SLL) are reported to have a mutation in Asc1, resulting in their susceptibility to AAL-toxin. We evaluated 119 ancestral tomato accessions including S. pimpinellifolium (SP), S. lycopersicum var. cerasiforme (SLC) and S. lycopersicum var. lycopersicum “jitomate criollo” (SLJ) for AAL-toxin susceptibility. Three accessions, SP PER018805, SLC PER018894, and SLJ M5-3, were susceptible to AAL-toxin. SLC PER018894 and SLJ M5-3 had a two-nucleotide deletion (nt 854_855del) in Asc1 identical to that found in SLL cv. Aichi-first. Another mutation (nt 931_932insT) that may confer AAL-toxin susceptibility was identified in SP PER018805. In the phylogenetic tree based on the 18 COSII sequences, a clade (S3) is composed of SP, including the AAL-toxin susceptible PER018805, and SLC. AAL-toxin susceptible SLC PER018894 and SLJ M5-3 were in Clade S2 with SLL cultivars. As SLC is thought to be the ancestor of SLL, and SLJ is an intermediate tomato between SLC and SLL, Asc1s with/without the mutation seem to have been inherited throughout the history of tomato domestication and breeding.

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Horizontal Chromosome Transfer, a Mechanism for the Evolution and Differentiation of a Plant-Pathogenic Fungus

Eukaryotic Cell ◽

10.1128/ec.00135-09 ◽

2009 ◽

Vol 8 (11) ◽

pp. 1732-1738 ◽

Cited By ~ 105

Author(s):

Yasunori Akagi ◽

Hajime Akamatsu ◽

Hiroshi Otani ◽

Motoichiro Kodama

Keyword(s):

Fragment Length Polymorphism ◽

Pathogenic Fungus ◽

Stem Canker ◽

Hybrid Strain ◽

Dispensable Chromosome ◽

Tomato Pathotype ◽

Aal Toxin ◽

Cdc Genes ◽

Restriction Fragment Length ◽

Alternaria Stem Canker

ABSTRACT The tomato pathotype of Alternaria alternata produces host-specific AAL toxin and causes Alternaria stem canker on tomato. A polyketide synthetase (PKS) gene, ALT1, which is involved in AAL toxin biosynthesis, resides on a 1.0-Mb conditionally dispensable chromosome (CDC) found only in the pathogenic and AAL toxin-producing strains. Genomic sequences of ALT1 and another PKS gene, both of which reside on the CDC in the tomato pathotype strains, were compared to those of tomato pathotype strains collected worldwide. This revealed that the sequences of both CDC genes were identical among five A. alternata tomato pathotype strains having different geographical origins. On the other hand, the sequences of other genes located on chromosomes other than the CDC are not identical in each strain, indicating that the origin of the CDC might be different from that of other chromosomes in the tomato pathotype. Telomere fingerprinting and restriction fragment length polymorphism analyses of the A. alternata strains also indicated that the CDCs in the tomato pathotype strains were identical, although the genetic backgrounds of the strains differed. A hybrid strain between two different pathotypes was shown to harbor the CDCs derived from both parental strains with an expanded range of pathogenicity, indicating that CDCs can be transmitted from one strain to another and stably maintained in the new genome. We propose a hypothesis whereby the ability to produce AAL toxin and to infect a plant could potentially be distributed among A. alternata strains by horizontal transfer of an entire pathogenicity chromosome. This could provide a possible mechanism by which new pathogens arise in nature.

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Fungal growth and in planta distribution of host-specific AAL-toxin in tomato plants infected with the tomato pathotype of Alternaria alternata

JSM Mycotoxins ◽

10.2520/myco.62.7 ◽

2012 ◽

Vol 62 (1) ◽

pp. 7-13 ◽

Cited By ~ 1

Author(s):

Ahmed A. KHEDER ◽

Yasunori AKAGI ◽

Kazumi TAKAO ◽

Hajime AKAMATSU ◽

Motoichiro KODAMA

Keyword(s):

Alternaria Alternata ◽

Fungal Growth ◽

In Planta ◽

Tomato Plants ◽

Tomato Pathotype ◽

Aal Toxin

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TMT-based quantitative proteomics analyses reveal novel defense mechanisms of Brassica napus against the devastating necrotrophic pathogen Sclerotinia sclerotiorum

Journal of Proteomics ◽

10.1016/j.jprot.2016.03.006 ◽

2016 ◽

Vol 143 ◽

pp. 265-277 ◽

Cited By ~ 14

Author(s):

Jia-Yi Cao ◽

You-Ping Xu ◽

Xin-Zhong Cai

Keyword(s):

Brassica Napus ◽

Sclerotinia Sclerotiorum ◽

Quantitative Proteomics ◽

Defense Mechanisms ◽

Necrotrophic Pathogen

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EDS1 Contributes to Nonhost Resistance of Arabidopsis thaliana Against Erwinia amylovora

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-05-11-0111 ◽

2012 ◽

Vol 25 (3) ◽

pp. 421-430 ◽

Cited By ~ 33

Author(s):

Manon Moreau ◽

Alexandre Degrave ◽

Régine Vedel ◽

Frédérique Bitton ◽

Oriane Patrit ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Protein Synthesis ◽

Erwinia Amylovora ◽

Gene Activation ◽

Negative Regulator ◽

Nonhost Resistance ◽

Callose Deposition ◽

In The Wild ◽

Increased Sensitivity ◽

Main Components

Erwinia amylovora causes fire blight in rosaceous plants. In nonhost Arabidopsis thaliana, E. amylovora triggers necrotic symptoms associated with transient bacterial multiplication, suggesting either that A. thaliana lacks a susceptibility factor or that it actively restricts E. amylovora growth. Inhibiting plant protein synthesis at the time of infection led to an increase in necrosis and bacterial multiplication and reduced callose deposition, indicating that A. thaliana requires active protein synthesis to restrict E. amylovora growth. Analysis of the callose synthase–deficient pmr4-1 mutant indicated that lack of callose deposition alone did not lead to increased sensitivity to E. amylovora. Transcriptome analysis revealed that approximately 20% of the genes induced following E. amylovora infection are related to defense and signaling. Analysis of mutants affected in NDR1 and EDS1, two main components of the defense-gene activation observed, revealed that E. amylovora multiplied ten times more in the eds1-2 mutant than in the wild type but not in the ndr1-1 mutant. Analysis of mutants affected in three WRKY transcription factors showing EDS1-dependent activation identified WRKY46 and WRKY54 as positive regulators and WRKY70 as a negative regulator of defense against E. amylovora. Altogether, we show that EDS1 is a positive regulator of nonhost resistance against E. amylovora in A. thaliana and hypothesize that it controls the production of several effective defenses against E. amylovora through the action of WRKY46 and WRKY54, while WRKY70 acts as a negative regulator.

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An Investigation into the Involvement of Defense Signaling Pathways in Components of the Nonhost Resistance of Arabidopsis thaliana to Rust Fungi Also Reveals a Model System for Studying Rust Fungal Compatibility

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2003.16.5.398 ◽

2003 ◽

Vol 16 (5) ◽

pp. 398-404 ◽

Cited By ~ 86

Author(s):

Denny G. Mellersh ◽

Michèle C. Heath

Keyword(s):

Arabidopsis Thaliana ◽

Rust Fungus ◽

Fungal Growth ◽

Rust Fungi ◽

Nonhost Resistance ◽

Wild Type ◽

Pr Genes ◽

Hypersensitive Cell Death ◽

Defense Signaling ◽

Infection Hypha

Seventeen accessions of Arabidopsis thaliana inoculated with the cowpea rust fungus Uromyces vignae exhibited a variety of expressions of nonhost resistance, although infection hypha growth typically ceased before the formation of the first haustorium, except in Ws-0. Compared with wild-type plants, there was no increased fungal growth in ndr1 or eds1 mutants defective in two of the signal cascades regulated by the major class of Arabidopsis host resistance genes. However, in the Col-0 background, infection hyphae of U. vignae and two other rust fungi were longer in sid2 mutants defective in an enzyme that synthesizes salicylic acid (SA), in npr1 mutants deficient in a regulator of the expression of SA-dependent pathogenesis related (PR) genes, and in NahG plants containing a bacterial salicylate hydroxylase. Infection hyphae of U. vignae and U. appendiculatus but not of Puccinia helianthi were also longer in jar1 mutants, which are defective in the jasmonic acid defense signaling pathway. Nevertheless, haustorium formation increased only for the Uromyces spp. and only in sid2 mutants or NahG plants. Rather than the hypersensitive cell death that usually accompanies haustorium formation in nonhost plants, Arabidopsis typically encased haustoria in calloselike material. Growing fungal colonies of both Uromyces spp., indicative of a successful biotrophic relationship between plant and fungus, formed in NahG plants, but only U. vignae formed growing colonies in the sid2 mutants and cycloheximide-treated wild-type plants. Growing colonies did not develop in NahG tobacco or tomato plants. These data suggest that nonhost resistance of Arabidopsis to rust fungi primarily involves the restriction of infection hypha growth as a result of defense gene expression. However, there is a subsequent involvement of SA but not SA-dependent PR genes in preventing the Uromyces spp. from forming the first haustorium and establishing a sufficient biotrophic relationship to support further fungal growth. The U. vignae-Arabidopsis combination could allow the application of the powerful genetic capabilities of this model plant to the study of compatibility as well as nonhost resistance to rust fungi.

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Pathogen Genetic Control of Transcriptome Variation in the Arabidopsis thaliana – Botrytis cinerea Pathosystem

Genetics ◽

10.1534/genetics.120.303070 ◽

2020 ◽

Vol 215 (1) ◽

pp. 253-266 ◽

Cited By ~ 2

Author(s):

Nicole E. Soltis ◽

Celine Caseys ◽

Wei Zhang ◽

Jason A. Corwin ◽

Susanna Atwell ◽

...

Keyword(s):

Gene Expression ◽

Arabidopsis Thaliana ◽

Botrytis Cinerea ◽

Gene Expression Regulation ◽

Expression Regulation ◽

Necrotrophic Pathogen ◽

Control Of Gene Expression ◽

Genome Wide ◽

Pathogen Control ◽

Transcriptome Variation

In plant–pathogen relations, disease symptoms arise from the interaction of the host and pathogen genomes. Host–pathogen functional gene interactions are well described, whereas little is known about how the pathogen genetic variation modulates both organisms’ transcriptomes. To model and generate hypotheses on a generalist pathogen control of gene expression regulation, we used the Arabidopsis thaliana–Botrytis cinerea pathosystem and the genetic diversity of a collection of 96 B. cinerea isolates. We performed expression-based genome-wide association (eGWA) for each of 23,947 measurable transcripts in Arabidopsis (host), and 9267 measurable transcripts in B. cinerea (pathogen). Unlike other eGWA studies, we detected a relative absence of locally acting expression quantitative trait loci (cis-eQTL), partly caused by structural variants and allelic heterogeneity hindering their identification. This study identified several distantly acting trans-eQTL linked to eQTL hotspots dispersed across Botrytis genome that altered only Botrytis transcripts, only Arabidopsis transcripts, or transcripts from both species. Gene membership in the trans-eQTL hotspots suggests links between gene expression regulation and both known and novel virulence mechanisms in this pathosystem. Genes annotated to these hotspots provide potential targets for blocking manipulation of the host response by this ubiquitous generalist necrotrophic pathogen.

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