A Breach in Plant Defences: Pseudomonas syringae pv. actinidiae Targets Ethylene Signalling to Overcome Actinidia chinensis Pathogen Responses

Ethylene interacts with other plant hormones to modulate many aspects of plant metabolism, including defence and stomata regulation. Therefore, its manipulation may allow plant pathogens to overcome the host’s immune responses. This work investigates the role of ethylene as a virulence factor for Pseudomonas syringae pv. actinidiae (Psa), the aetiological agent of the bacterial canker of kiwifruit. The pandemic, highly virulent biovar of this pathogen produces ethylene, whereas the biovars isolated in Japan and Korea do not. Ethylene production is modulated in planta by light/dark cycle. Exogenous ethylene application stimulates bacterial virulence, and restricts or increases host colonisation if performed before or after inoculation, respectively. The deletion of a gene, unrelated to known bacterial biosynthetic pathways and putatively encoding for an oxidoreductase, abolishes ethylene production and reduces the pathogen growth rate in planta. Ethylene production by Psa may be a recently and independently evolved virulence trait in the arms race against the host. Plant- and pathogen-derived ethylene may concur in the activation/suppression of immune responses, in the chemotaxis toward a suitable entry point, or in the endophytic colonisation.

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The Role of Ethylene Production in Virulence of Pseudomonas syringae pvs. glycinea and phaseolicola

Phytopathology ◽

10.1094/phyto.2001.91.5.511 ◽

2001 ◽

Vol 91 (5) ◽

pp. 511-518 ◽

Cited By ~ 60

Author(s):

Helge Weingart ◽

Henriette Ullrich ◽

Klaus Geider ◽

Beate Völksch

Keyword(s):

Pseudomonas Syringae ◽

Ethylene Production ◽

Type Strain ◽

Wild Type Strain ◽

Wild Type ◽

In Planta ◽

Population Sizes ◽

Soybean Plants ◽

Type Strains

The importance of ethylene production for virulence of Pseudomonas syringae pvs. glycinea and phaseolicola was assayed by comparing bacterial multiplication and symptom development in bean and soybean plants inoculated with ethylene-negative (efe) mutants and wild-type strains. The efe mutants of Pseudomonas syringae pv. glycinea were significantly reduced in their ability to grow in planta. However, the degree of reduction was strain-dependent. Population sizes of efe mutant 16/83-E1 that did not produce the phototoxin coronatine were 10- and 15-fold lower than those of the wild-type strain on soybean and on bean, and 16/83-E1 produced very weak symptoms compared with the wild-type strain. The coronatine-producing efe mutant 7a/90-E1 reached fourfold and twofold lower population sizes compared with the wild-type strain on soybean and bean, respectively, and caused disease symptoms typical of the wild-type strain. Experiments with ethylene-insensitive soybeans confirmed these results. The virulence of the wild-type strains was reduced to the same extent in ethylene-insensitive soybean plants as the virulence of the efe mutants in ethylene-susceptible soybeans. In contrast, the virulence of Pseudomonas syringae pv. phaseolicola was not affected by disruption of the efe gene.

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In planta bacterial multi-omics analysis illuminates regulatory principles underlying plant-pathogen interactions

10.1101/822932 ◽

2019 ◽

Cited By ~ 1

Author(s):

Tatsuya Nobori ◽

Yiming Wang ◽

Jingni Wu ◽

Sara Christina Stolze ◽

Yayoi Tsuda ◽

...

Keyword(s):

Gene Regulation ◽

Pseudomonas Syringae ◽

Protein Level ◽

Plant Pathogens ◽

Plant Immunity ◽

Bacterial Pathogen ◽

Bacterial Virulence ◽

In Planta ◽

Bacterial Gene ◽

Global Food Security

AbstractUnderstanding how gene expression is regulated in plant pathogens is crucial for pest control and thus global food security. An integrated understanding of bacterial gene regulation in the host is dependent on multi-omic datasets, but these are largely lacking. Here, we simultaneously characterized the transcriptome and proteome of a foliar bacterial pathogen, Pseudomonas syringae, in Arabidopsis thaliana and identified a number of bacterial processes influenced by plant immunity at the mRNA and the protein level. We found instances of both concordant and discordant regulation of bacterial mRNAs and proteins. Notably, the tip component of bacterial type III secretion system was selectively suppressed by the plant salicylic acid pathway at the protein level, suggesting protein-level targeting of the bacterial virulence system by plant immunity. Furthermore, gene co-expression analysis illuminated previously unknown gene regulatory modules underlying bacterial virulence and their regulatory hierarchy. Collectively, the integrated in planta bacterial omics approach provides molecular insights into multiple layers of bacterial gene regulation that contribute to bacterial growth in planta and elucidate the role of plant immunity in controlling pathogens.

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Identification of Loci of Pseudomonas syringae pv. actinidiae Involved in Lipolytic Activity and Their Role in Colonization of Kiwifruit Leaves

Phytopathology ◽

10.1094/phyto-10-16-0360-r ◽

2017 ◽

Vol 107 (6) ◽

pp. 645-653 ◽

Cited By ~ 2

Author(s):

Hitendra Kumar Patel ◽

Patrizia Ferrante ◽

Meng Xianfa ◽

Sree Gowrinadh Javvadi ◽

Sujatha Subramoni ◽

...

Keyword(s):

Pseudomonas Syringae ◽

Plant Pathogens ◽

Lipid A ◽

Lipolytic Activity ◽

Genetic Screen ◽

Economic Losses ◽

In Planta ◽

Tn5 Transposon ◽

Tn5 Mutants ◽

Transposon Mutants

Bacterial canker disease caused by Pseudomonas syringae pv. actinidiae, an emerging pathogen of kiwifruit plants, has recently brought about major economic losses worldwide. Genetic studies on virulence functions of P. syringae pv. actinidiae have not yet been reported and there is little experimental data regarding bacterial genes involved in pathogenesis. In this study, we performed a genetic screen in order to identify transposon mutants altered in the lipolytic activity because it is known that mechanisms of regulation, production, and secretion of enzymes often play crucial roles in virulence of plant pathogens. We aimed to identify the set of secretion and global regulatory loci that control lipolytic activity and also play important roles in in planta fitness. Our screen for altered lipolytic activity phenotype identified a total of 58 Tn5 transposon mutants. Mapping all these Tn5 mutants revealed that the transposons were inserted in genes that play roles in cell division, chemotaxis, metabolism, movement, recombination, regulation, signal transduction, and transport as well as a few unknown functions. Several of these identified P. syringae pv. actinidiae Tn5 mutants, notably the functions affected in phosphomannomutase AlgC, lipid A biosynthesis acyltransferase, glutamate–cysteine ligase, and the type IV pilus protein PilI, were also found affected in in planta survival and/or growth in kiwifruit plants. The results of the genetic screen and identification of novel loci involved in in planta fitness of P. syringae pv. actinidiae are presented and discussed.

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Insights into the cell-cell signaling and iron homeostasis in Xanthomonas virulence and lifestyle

Phytopathology ◽

10.1094/phyto-11-20-0513-rvw ◽

2021 ◽

Author(s):

Sheo Shankar Pandey ◽

Subhadeep Chatterjee

Keyword(s):

Cell Signaling ◽

Plant Pathogens ◽

Iron Homeostasis ◽

Yield Loss ◽

Iron Availability ◽

In Planta ◽

Xanthomonas Species ◽

Associated Functions ◽

Cell Cell

The Xanthomonas group of phytopathogens causes economically important diseases, which cause severe yield loss in major crops. Some Xanthomonas species are known to have an epiphytic and in planta lifestyle which are coordinated by several virulence-associated functions, cell-cell signaling (DSF; diffusible signaling factor), and environmental conditions, including iron availability. In this review, we described the role of cell-cell signaling by the DSF molecule and iron in the regulation of virulence-associated functions. Although DSF and iron are involved in the regulation of several virulence-associated functions, members of the Xanthomonas group of plant pathogens exhibit atypical patterns of regulation. Atypical patterns contribute to the adaptation to different lifestyles. Studies on DSF and iron biology indicate that virulence-associated functions can be regulated in completely contrasting fashions by the same signaling system in closely related xanthomonads.

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Characterization of the RND-Type Multidrug Efflux Pump MexAB-OprM of the Plant Pathogen Pseudomonas syringae

Applied and Environmental Microbiology ◽

10.1128/aem.02866-07 ◽

2008 ◽

Vol 74 (11) ◽

pp. 3387-3393 ◽

Cited By ~ 45

Author(s):

Savina O. Stoitsova ◽

Yvonne Braun ◽

Matthias S. Ullrich ◽

Helge Weingart

Keyword(s):

Pseudomonas Syringae ◽

Plant Pathogens ◽

Efflux Pump ◽

Blot Hybridization ◽

In Planta ◽

Multidrug Efflux ◽

Dot Blot ◽

Multidrug Efflux Pump

ABSTRACT In gram-negative bacteria, transporters belonging to the RND family are the transporters most relevant for resistance to antimicrobial compounds. In Pseudomonas aeruginosa, a clinically important pathogen, the RND-type pump MexAB-OprM has been recognized as one of the major multidrug efflux systems. Here, homologues of MexAB-OprM in the plant pathogens Pseudomonas syringae pv. phaseolicola 1448A, P. syringae pv. syringae B728a, and P. syringae pv. tomato DC3000 were identified, and mexAB-oprM-deficient mutants were generated. Determination of MICs revealed that mutation of MexAB-OprM dramatically reduced the tolerance to a broad range of antimicrobials. Moreover, the ability of the mexAB-oprM-deficient mutants to multiply in planta was reduced. RNA dot blot hybridization revealed growth-dependent regulation of the mexAB-oprM operon in P. syringae; the expression of this operon was maximal in early exponential phase and decreased gradually during further growth.

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Perturbations of a Kinase-Pseudokinase Module Activate Plant Immunity

10.1101/531665 ◽

2019 ◽

Author(s):

D. Patrick Bastedo ◽

Derek Seto ◽

Alexandre Martel ◽

Madiha Khan ◽

Inga Kireeva ◽

...

Keyword(s):

Immune Response ◽

Arabidopsis Thaliana ◽

Immune Responses ◽

Pseudomonas Syringae ◽

Molecular Mechanisms ◽

Kinase Domain ◽

Host Cells ◽

In Planta ◽

Plant Host ◽

Model Plant

ABSTRACTThe Pseudomonas syringae acetyltransferase HopZ1a is delivered directly into host cells by the type III secretion system to promote bacterial growth. However, in the model plant host Arabidopsis thaliana, HopZ1a activity results in an effector-triggered immune response (ETI) that limits bacterial proliferation. HopZ1a-triggered immunity requires the nucleotide-binding, leucine-rich repeat domain (NLR) protein, ZAR1, and the ZED1 pseudokinase. Here we demonstrate that HopZ1a can acetylate members of a family of ‘receptor-like cytoplasmic kinases’ (RLCK family VII; also known as PBS1-like kinases, or PBLs) and promote their interaction with ZED1 and ZAR1 to form a ZAR1/ZED1/PBL ternary complex. Interactions between ZED1 and PBL kinases are determined by the pseudokinase features of ZED1, and mutants designed to restore ZED1 kinase motifs can (1) bind to PBLs, (2) recruit ZAR1, and (3) trigger immunity in planta, all independently of HopZ1a. Our results suggest that interactions between these two RLCK families are promoted by perturbations of structural features that distinguish active from inactive kinase domain conformations. We propose that effector-induced interactions between ZED1/ZRK pseudokinases (RLCK family XII) and PBL kinases (RLCK family VII) provide a sensitive mechanism for detecting perturbations of either kinase family and activating ZAR1-mediated ETI.AUTHOR SUMMARYAll plants must ward off potentially infectious microbes, and those grown in large-scale crop operations are especially vulnerable to the rapid spread of disease by successful pathogens. Although many bacteria and fungi can supress plant immune responses by producing specialized virulence proteins called ‘effectors’, these effectors can also trigger immune responses that render plants resistant to infection. We studied the molecular mechanisms underlying one such effector-triggered immune response elicited by the bacterial effector HopZ1a in the model plant host Arabidopsis thaliana. We have shown that HopZ1a promotes binding between a ZED1, a ‘pseudokinase’ required for HopZ1a-triggered immunity, and several ‘true kinases’ (known as PBLs) that are likely targets of HopZ1a activity in planta. HopZ1a-induced ZED1-PBL interactions also recruit ZAR1, an Arabidopsis ‘resistance protein’ previously implicated in HopZ1a-triggered immunity. Importantly, ZED1 mutants that restore degenerate kinase motifs can bridge interactions between PBLs and ZAR1 (independently of HopZ1a) and trigger immunity in planta. Our results suggest that equilibria between active and inactive kinase domain conformations regulate ZED1-PBL interactions and formation of ternary complexes with ZAR1. Improved models describing molecular interactions between immunity determinants, effectors and effector targets will inform efforts to exploit natural diversity for development of crops with enhanced disease resistance.

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Phevamine A, a small molecule that suppresses plant immune responses

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1803779115 ◽

2018 ◽

Vol 115 (41) ◽

pp. E9514-E9522 ◽

Cited By ~ 10

Author(s):

Erinn M. O’Neill ◽

Tatiana S. Mucyn ◽

Jon B. Patteson ◽

Omri M. Finkel ◽

Eui-Hwan Chung ◽

...

Keyword(s):

Immune Responses ◽

Small Molecules ◽

Pseudomonas Syringae ◽

Small Molecule ◽

Virulence Factor ◽

Plant Pathogens ◽

Crop Damage ◽

Host Interactions ◽

Potentiation Effect ◽

Reactive Oxygen Species Burst

Bacterial plant pathogens cause significant crop damage worldwide. They invade plant cells by producing a variety of virulence factors, including small-molecule toxins and phytohormone mimics. Virulence of the model pathogen Pseudomonas syringae pv. tomato DC3000 (Pto) is regulated in part by the sigma factor HrpL. Our study of the HrpL regulon identified an uncharacterized, three-gene operon in Pto that is controlled by HrpL and related to the Erwinia hrp-associated systemic virulence (hsv) operon. Here, we demonstrate that the hsv operon contributes to the virulence of Pto on Arabidopsis thaliana and suppresses bacteria-induced immune responses. We show that the hsv-encoded enzymes in Pto synthesize a small molecule, phevamine A. This molecule consists of l-phenylalanine, l-valine, and a modified spermidine, and is different from known small molecules produced by phytopathogens. We show that phevamine A suppresses a potentiation effect of spermidine and l-arginine on the reactive oxygen species burst generated upon recognition of bacterial flagellin. The hsv operon is found in the genomes of divergent bacterial genera, including ∼37% of P. syringae genomes, suggesting that phevamine A is a widely distributed virulence factor in phytopathogens. Our work identifies a small-molecule virulence factor and reveals a mechanism by which bacterial pathogens overcome plant defense. This work highlights the power of omics approaches in identifying important small molecules in bacteria–host interactions.

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Diurnal down-regulation of ethylene biosynthesis mediates biomass heterosis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1722068115 ◽

2018 ◽

Vol 115 (21) ◽

pp. 5606-5611 ◽

Cited By ~ 12

Author(s):

Qingxin Song ◽

Atsumi Ando ◽

Dongqing Xu ◽

Lei Fang ◽

Tianzhen Zhang ◽

...

Keyword(s):

Biological Networks ◽

Ethylene Production ◽

Molecular Mechanisms ◽

Ethylene Biosynthesis ◽

Superior Performance ◽

F1 Hybrids ◽

Down Regulation ◽

Negative Role ◽

Exogenous Ethylene

Heterosis is widely applied in agriculture; however, the underlying molecular mechanisms for superior performance are not well understood. Ethylene biosynthesis and signaling genes are shown to be down-regulated in Arabidopsis interspecific hybrids. Ethylene is a plant hormone that promotes fruit ripening and maturation but inhibits hypocotyl elongation. Here we report that application of exogenous ethylene could eliminate biomass vigor in Arabidopsis thaliana F1 hybrids, suggesting a negative role of ethylene in heterosis. Ethylene biosynthesis is mediated by the rate-limiting enzyme, 1-aminocyclopropane-1-carboxylate synthase (ACS). Down-regulation of ACS genes led to the decrease of ethylene production, which was associated with the high-vigor F1 hybrids, but not with the low-vigor ones. At the mechanistic level, expression of ACS genes was down-regulated diurnally and indirectly by Circadian Clock Associated 1 (CCA1) during the day and directly by Phyotochrome-Interacting Factor 5 (PIF5) at night. Consistent with the negative role of ethylene in plant growth, biomass vigor was higher in the acs mutants than in wild-type plants, while increasing endogenous ethylene production in the hybridizing parents reduced growth vigor in the hybrids. Thus, integrating circadian rhythms and light signaling into ethylene production is another regulatory module of complex biological networks, leading to biomass heterosis in plants.

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Re-evaluation of ethylene role in Arabidopsis cauline leaf abscission induced by water stress and rewatering

10.1101/2021.09.27.462018 ◽

2021 ◽

Author(s):

Shimon Meir ◽

Sonia Philosoph-Hadas ◽

Shoshana Salim ◽

Adi Segev ◽

Joseph Riov

Keyword(s):

Water Stress ◽

Ethylene Production ◽

Leaf Abscission ◽

Wild Type ◽

Cauline Leaf ◽

Arabidopsis Mutants ◽

Endogenous Ethylene ◽

Exogenous Ethylene ◽

Established Role

ABSTRACTPatharkar and Walker (2016) reported that cauline leaf abscission in Arabidopsis is induced by a cycle of water stress and rewatering, which is regulated by the complex of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), HAESA (HAE), and HAESA-LIKE2 (HSL2) kinases. However, they stated without presenting experimental results that ethylene is not involved in this process. Since this statement contradicts the well-established role of ethylene in organ abscission induced by a cycle of water stress and rewatering, our present study was aimed to re-evaluate the possible involvement of ethylene in this process. For this purpose, we examined the endogenous ethylene production during water stress and following rewatering, as well as the effects of exogenous ethylene and 1-methylcyclopropene (1-MCP), on cauline leaf abscission of Arabidopsis wild type. Additionally, we examined whether this stress induces cauline leaf abscission in ethylene-insensitive Arabidopsis mutants. The results of the present study demonstrated that ethylene production rates increased significantly in cauline leaves at 4 h after rewatering of stressed plants, and remained high for at least 24 h in plants water-stressed to 40 and 30% of system weight. Ethylene treatment applied to well-watered plants induced cauline leaf abscission, which was inhibited by 1-MCP. Cauline leaf abscission was also inhibited by 1-MCP applied during a cycle of water stress and rewatering. Finally, no abscission occurred in two ethylene-insensitive mutants, ein2-1 and ein2-5, following a cycle of water stress and rewatering. Taken together, these results clearly indicate that ethylene is involved in Arabidopsis cauline leaf abscission induced by water stress.One sentence summaryUnlike Patharker and Walker (2016), our results show that ethylene is involved in Arabidopsis cauline leaf abscission induced by water stress and rewatering, similar to leaf abscission in other plants.

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Perception of structurally distinct effectors by the integrated WRKY domain of a plant immune receptor.

10.1101/2021.07.28.454147 ◽

2021 ◽

Author(s):

Nitika Mukhi ◽

Hannah Brown ◽

Danylo Gorenkin ◽

Pingtao Ding ◽

Adam R Bentham ◽

...

Keyword(s):

Crystal Structure ◽

Immune Responses ◽

Pseudomonas Syringae ◽

Effector Proteins ◽

Dna Binding Domain ◽

Binding Affinities ◽

Wrky Domain ◽

In Planta ◽

Integrated Domains

Plants use intracellular immune receptors (NLRs) to detect pathogen-derived effector proteins. The Arabidopsis NLR pair RRS1-R/RPS4 confers disease resistance to different bacterial pathogens by perceiving structurally distinct effectors AvrRps4 from Pseudomonas syringae pv. pisi and PopP2 from Ralstonia solanacearum via an integrated WRKY domain in RRS1-R. How the WRKY domain of RRS1 (RRS1WRKY) perceives distinct classes of effector to initiate an immune response is unknown. We report here the crystal structure of the in planta processed C-terminal domain of AvrRps4 (AvrRps4C) in complex with RRS1WRKY. Perception of AvrRps4C by RRS1WRKY is mediated by the β2-β3 segment of RRS1WRKY that binds an electronegative patch on the surface of AvrRps4C. Structure-based mutations that disrupt AvrRps4C/RRS1WRKY interactions in vitro compromise RRS1/RPS4-dependent immune responses. We also show that AvrRps4C can associate with the WRKY domain of the related but distinct RRS1B/RPS4B NLR pair, and the DNA binding domain of AtWRKY41, with similar binding affinities. This work demonstrates how integrated domains in plant NLRs can directly bind structurally distinct effectors to initiate immunity.

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