The Ralstonia pseudosolanacearum Type III Effector RipL Delays Flowering and Promotes Susceptibility to Pseudomonas syringae in Arabidopsis thaliana

Cécile Segonzac,김완희,Hyelim Jeon,Kee Hoon Sohn 한국분자세포생물학회 2023 Molecules and cells Vol.46 No.11

The plant defense responses to microbial infection are tightly regulated and integrated with the developmental program for optimal resources allocation. Notably, the defense- associated hormone salicylic acid (SA) acts as a promoter of flowering while several plant pathogens actively target the flowering signaling pathway to promote their virulence or dissemination. Ralstonia pseudosolanacearum inject tens of effectors in the host cells that collectively promote bacterial proliferation in plant tissues. Here, we characterized the function of the broadly conserved R. pseudosolanacearum effector RipL, through heterologous expression in Arabidopsis thaliana . RipL-expressing transgenic lines presented a delayed flowering, which correlated with a low expression of flowering regulator genes. Delayed flowering was also observed in Nicotiana benthamiana plants transiently expressing RipL. In parallel, RipL promoted plant susceptibility to virulent strains of Pseudomonas syringae in the effector-expressing lines or when delivered by the type III secretion system. Unexpectedly, SA accumulation and SA-dependent immune signaling were not significantly affected by RipL expression. Rather, the RNA-seq analysis of infected RipL-expressing lines revealed that the overall amplitude of the transcriptional response was dampened, suggesting that RipL could promote plant susceptibility in an SA-independent manner. Further elucidation of the molecular mechanisms underpinning RipL effect on flowering and immunity may reveal novel effector functions in host cells.

[PF-0002] A new NLR mediates RipY recognition from Ralstonia solanacearum phylotype I in Nicotiana benthamiana

Boyoung Kim(Boyoung Kim),Hyein Yu(Hyein Yu),Cécile Segonzac(Cécile Segonzac ) 한국육종학회 2022 한국육종학회 공동학술발표집 Vol.2022 No.-

The Nuclear Immune Receptor <i>RPS4</i> Is Required for <i>RRS1^SLH1</i> -Dependent Constitutive Defense Activation in <i>Arabidopsis thaliana</i>

Sohn, Kee Hoon,Segonzac, Cé,cile,Rallapalli, Ghanasyam,Sarris, Panagiotis F.,Woo, Joo Yong,Williams, Simon J.,Newman, Toby E.,Paek, Kyung Hee,Kobe, Bostjan,Jones, Jonathan D. G. Public Library of Science 2014 PLoS genetics Vol.10 No.10

<▼1><P>Plant nucleotide-binding leucine-rich repeat (NB-LRR) disease resistance (R) proteins recognize specific “avirulent” pathogen effectors and activate immune responses. NB-LRR proteins structurally and functionally resemble mammalian Nod-like receptors (NLRs). How NB-LRR and NLR proteins activate defense is poorly understood. The divergently transcribed Arabidopsis <I>R</I> genes, <I>RPS4</I> (resistance to <I>Pseudomonas syringae</I> 4) and <I>RRS1</I> (resistance to <I>Ralstonia solanacearum</I> 1), function together to confer recognition of <I>Pseudomonas</I> AvrRps4 and <I>Ralstonia</I> PopP2. <I>RRS1</I> is the only known recessive NB-LRR <I>R</I> gene and encodes a WRKY DNA binding domain, prompting suggestions that it acts downstream of RPS4 for transcriptional activation of defense genes. We define here the early RRS1-dependent transcriptional changes upon delivery of PopP2 <I>via Pseudomonas</I> type III secretion. The Arabidopsis <I>slh1</I> (<I>sensitive to low humidity 1</I>) mutant encodes an RRS1 allele (RRS1<SUP>SLH1</SUP>) with a single amino acid (leucine) insertion in the WRKY DNA-binding domain. Its poor growth due to constitutive defense activation is rescued at higher temperature. Transcription profiling data indicate that RRS1<SUP>SLH1</SUP>-mediated defense activation overlaps substantially with AvrRps4- and PopP2-regulated responses. To better understand the genetic basis of RPS4/RRS1-dependent immunity, we performed a genetic screen to identify <I><U>su</U>ppressor of</I><U>s</U>l<U>h</U>1 <I><U>i</U>mmunity</I> (<I>sushi</I>) mutants. We show that many <I>sushi</I> mutants carry mutations in <I>RPS4</I>, suggesting that RPS4 acts downstream or in a complex with RRS1. Interestingly, several mutations were identified in a domain C-terminal to the RPS4 LRR domain. Using an <I>Agrobacterium</I>-mediated transient assay system, we demonstrate that the P-loop motif of RPS4 but not of RRS1<SUP>SLH1</SUP> is required for RRS1<SUP>SLH1</SUP> function. We also recapitulate the dominant suppression of RRS1<SUP>SLH1</SUP> defense activation by wild type RRS1 and show this suppression requires an intact RRS1 P-loop. These analyses of RRS1<SUP>SLH1</SUP> shed new light on mechanisms by which NB-LRR protein pairs activate defense signaling, or are held inactive in the absence of a pathogen effector.</P></▼1><▼2><P><B>Author Summary</B></P><P>How plant NB-LRR resistance proteins and the related mammalian Nod-like receptors (NLRs) activate defense is poorly understood. Plant and animal immune receptors can function in pairs. Two Arabidopsis nuclear immune receptors, RPS4 and RRS1, confer recognition of the unrelated bacterial effectors, AvrRps4 and PopP2, and activate defense. Using delivery of PopP2 into Arabidopsis leaf cells <I>via Pseudomonas</I> type III secretion, we define early transcriptional changes upon RPS4/RRS1-dependent PopP2 recognition. We show an auto-active allele of RRS1, RRS1<SUP>SLH1</SUP>, triggers transcriptional reprogramming of defense genes that are also reprogrammed by AvrRps4 or PopP2 in an RPS4/RRS1-dependent manner. To discover genetic requirements for RRS1<SUP>SLH1</SUP> auto-activation, we conducted a suppressor screen. Many <I>suppressor of</I> slh1 <I>immunity</I> (<I>sushi</I>) mutants that are impaired in RRS1<SUP>SLH1</SUP>-mediated auto-activation carry loss-of-function mutations in RPS4. This suggests that RPS4 functions as a signaling component together with or downstream of RRS1-activated immunity, in contrast to earlier hypotheses, significantly advancing our understanding of how immune receptors activate defense in plants.</P></▼2>

Tackling multiple bacterial diseases of Solanaceae with a handful of immune receptors

Ho Bang Kim,최지현,Cécile Segonzac 한국원예학회 2022 Horticulture, Environment, and Biotechnology Vol.63 No.2

Every year, despite the use of chemicals, signifi cant crop loss is caused by pathogenic microbes. Plant innate resistance to pathogens depends on two sets of genetically encoded immune receptors that sense invaders and trigger signaling cascades leading to reinforcement of physical barriers and production of various antimicrobial compounds. In the past 30 years, the molecular cloning and characterization of plant immune receptors have deepened our understanding of the plant immune system and more importantly, have provided means to improve crop protection against devastating pathogens. Here, we review the molecular characterization of selected immune receptors that can detect multiple species of bacterial pathogens through an expanded recognition range, or through the detection of conserved pathogen activities or host targets. These recent structural and molecular insights about the activation of immune receptors provide the necessary framework to design their concomitant deployment in crops, in order to lower selective pressure on pathogen populations and prevent evasion from recognition. Hence, these few immune receptors emerge as high potential genetic resources to provide durable and environmentally safe protection against important bacterial diseases of solanaceous crops.

An Alternative Method to Evaluate Resistance to Pear Scab (Venturia nashicola)

Kyungho Won,Eu Ddeum Choi,Keumsun Kim,Hae Won Jung,Il Sheob Shin,Seongsig Hong,Cécile Segonzac,Young Jin Kim 한국식물병리학회 2023 Plant Pathology Journal Vol.39 No.2

Two pear cultivars with different degrees of resistance to Venturia nashicola were evaluated on the basis of a disease severity rating for pear scab resistance under controlled environmental condition. Two inoculation techniques were tested: the procedure for inoculation by dropping conidia suspension of V. nashicola; the procedure by deposition of agar plug on the abaxial surface of pear leaves. All tested cultivars resulted in blight symptoms on the inoculated leaves and became spread to uninoculated region or other leaves. Although both methods provide satisfactory infection of V. nashicola on pear leaves, the mycelial plug method of inoculation was more reliable than the spray inoculation method for the evaluation of pear scab disease resistance. The incubation period of V. nashicola in the resistant pear cultivar, Greensis was longer than that in the susceptible cultivar, Hwasan.

Whole Genome Enabled Phylogenetic and Secretome Analyses of Two Venturia nashicola Isolates

Maxim Prokchorchik,Kyungho Won,Yoonyoung Lee,Cé,cile Segonzac,Kee Hoon Sohn 한국식물병리학회 2020 Plant Pathology Journal Vol.36 No.1

Venturia nashicola is a fungal pathogen causing scab disease in Asian pears. It is particularly important in the Northeast Asia region where Asian pears are intensively grown. Venturia nashicola causes disease in Asian pear but not in European pear. Due to the highly restricted host range of Venturia nashicola, it is hypothesized that the small secreted proteins deployed by the pathogen are responsible for the host determination. Here we report the whole genome based phylogenetic analysis and predicted secretomes for V. nashicola isolates. We believe that our data will provide a valuable information for further validation and functional characterization of host determinants in V. nashicola.

A Bacterial Tyrosine Phosphatase Inhibits Plant Pattern Recognition Receptor Activation

Macho, Alberto P.,Schwessinger, Benjamin,Ntoukakis, Vardis,Brutus, Alexandre,Segonzac, Cé,cile,Roy, Sonali,Kadota, Yasuhiro,Oh, Man-Ho,Sklenar, Jan,Derbyshire, Paul,Lozano-Durá,n, Rosa,Mal American Association for the Advancement of Scienc 2014 Science Vol.343 No.6178

<P><B>Move and Countermove</B></P><P>Receptors on plant cell surfaces are tuned to recognize molecular patterns associated with pathogenic bacteria. <B>Macho <I>et al.</I></B> (p. 1509; published online 13 March) found that activation of one of these receptors in <I>Arabidopsis</I> results in phosphorylation of a specific tyrosine residue, which in turn triggers the plant's immune response to the phytopathogen <I>Pseudomonas syringae. P. syringae</I> counters by secreting a specifically targeted phosphatase, thus stalling the plant's immune response.</P>

Ralstonia solanacearum Type III Effectors with Predicted Nuclear Localization Signal Localize to Various Cell Compartments and Modulate Immune Responses in Nicotiana spp.

Hyelim Jeon,Wanhui Kim,Boyoung Kim,Sookyeong Lee,Jay Jayaraman,Gayoung Jung,Sera Choi,Kee Hoon Sohn,Cé,cile Segonzac 한국식물병리학회 2020 Plant Pathology Journal Vol.36 No.1

Ralstonia solanacearum (Rso) is a causal agent of bacterial wilt in Solanaceae crops worldwide including Republic of Korea. Rso virulence predominantly relies on type III secreted effectors (T3Es). However, only a handful of Rso T3Es have been characterized. In this study, we investigated subcellular localization of and manipulation of plant immunity by 8 Rso T3Es predicted to harbor a nuclear localization signal (NLS). While 2 of these T3Es elicited cell death in both Nicotiana benthamiana and N. tabacum, only one was dependent on suppressor of G2 allele of skp1 (SGT1), a molecular chaperone of nucleotide-binding and leucine-rich repeat immune receptors. We also identified T3Es that differentially regulate flg22-induced reactive oxygen species production and gene expression. Interestingly, several of the NLS-containing T3Es translationally fused with yellow fluorescent protein accumulated in subcellular compartments other than the cell nucleus. Our findings bring new clues to decipher Rso T3E function in planta.