Biology subjects

Segonzac, C.

Publications and source records attributed to Segonzac, C..

8 recordsLinked to original sources

bioRxiv2026

Solanum americanum Bs2 and ZAR1 homologs recognize Xanthomonas euvesicatoria effectors essential for infection.

Multiple recognition events of pathogen-secreted effectors by immune receptors confer robust disease resistance in plants. Understanding the underlying mechanisms facilitates the discovery and deployment of valuable resistance genes for crop protection. Xanthomonas euvesicatoria causes devastating bacterial spot disease in solanaceous crops but cannot infect the wild relative Solanum americanum. Here, we identified X. euvesicatoria type III effectors (T3Es) that induce cell death in S. americanum when transiently expressed in leaf. By quantifying immune responses of the S. americanum SP2273 accession to X. euvesicatoria multiple-T3E knockout mutants, we demonstrated that at least nine T3Es (AvrBs2, XopAP, XopAU, XopE1, XopJ3, XopM, XopN, XopX, and XopZ1) collectively contribute to effector-triggered immunity (ETI). Among these, AvrBs2 and XopJ3 were the primary drivers of ETI, eliciting robust cell death and defense gene expression when naturally delivered into plant cells. We next generated S. americanum lines concomitantly edited at the corresponding immune receptor loci, SaBs2 and SaZAR1 (SP2273-bz). Genetic complementation of SP2273-bz confirmed that AvrBs2 and XopJ3 are specifically recognized by each of the four SaBs2 homologs and by SaZAR1, respectively. Moreover, enhanced growth of X. euvesicatoria on the characterized SP2273-bz line indicated that both effectors are required for bacterial multiplication in S. americanum. Together, our findings provide a framework for understanding the mechanisms of ETI-mediated resistance and establish a genetic foundation for resistance breeding in solanaceous crops.

plant biology↗

bioRxiv2026

Biochemical regulation of Arabidopsis PUB33: a receptor-like cytoplasmic kinase with an integrated U-box domain that ubiquitinates Ralstonia pseudosolanacearum effector protein RipV1

Plant immunity relies on the detection of microbes and the rapid activation of intracellular defense pathways. Catalyzed by protein kinases and E3 ubiquitin ligases, respectively, phosphorylation and ubiquitination are among the most abundant post-translational modifications that regulate immune pathways. It has been well established that members of the receptor-like cytoplasmic kinase (RLCK) and plant U-box E3 ligase (PUB) families are critical components of plant immune signaling. Interestingly, a group of proteins that contain both an RLCK domain and a PUB domain has been conserved throughout plant evolution, referred to as subgroups RLCK-IXb and PUB-VI within their respective families. While very little is known about these proteins, evidence from multiple independent studies indicates that orthologous PUB-VI/RLCK-IXb proteins in potato, tomato, Nicotiana benthamiana, and Arabidopsis thaliana associate with diverse pathogen effectors from the oomycete pathogen Phytophthora infestans, bacterial pathogen Ralstonia pseudosolanacearum, and the mirid bug Apolygus lucorum, suggesting that they may be critical virulence targets or components of the immune response. However, the biochemical activities of these proteins and how they contribute to plant health remain poorly defined. Here, we introduce the PUB-VI/RLCK-IXb clade in Arabidopsis, focusing on PUB32, PUB33, and PUB50. We show that PUB33 exhibits dual kinase and E3 ubiquitin ligase activities that are inversely regulated by autophosphorylation at Thr333. PUB33 forms homomers and heteromers with PUB32 which attenuate PUB33 catalytic activity. Although we did not observe clear defects in innate immune signaling in pub32, pub33, or pub50 mutants, we found that overexpression of PUB33 can suppress cell death triggered by the R. pseudosolanacearum effector RipV1 in N. benthamiana. Moreover, PUB33 directly ubiquitinates RipV1 in vitro and reduces RipV1 accumulation in planta, suggesting that it functions as part of the immune response against R. pseudosolanacearum.

plant biology↗

bioRxiv2025

The Ralstonia solanacearum E3 ligase effector RipV1 targets subfamily IXb receptor-like cytoplasmic kinases that negatively regulate immunity in Nicotiana benthamiana.

Plants detect microbe-associated molecular patterns from pathogens via plasma membrane- localized receptors which activate multiple signaling cascades that lead to pattern-triggered immunity (PTI). Receptor-like cytoplasmic kinases (RLCKs) are essential hubs of plant immune signaling, associating with receptors and intracellular proteins through phosphorylation events. As a consequence, RLCKs have emerged as common targets of pathogen effectors. To improve our knowledge on Solanaceae responses to the bacterial wilt pathogen Ralstonia solanacearum, we conducted a yeast two-hybrid screen between tomato RLCKs and effectors conserved in R. solanacearum Korean isolates. Several members of RLCK subfamily IXb, which contain a ubiquitin-ligase plant U-box domain in addition to the kinase domain, interacted with RipV1, an effector containing a novel E3 ligase domain (NEL). In vitro assays revealed that RLCK-IXb-1 displayed ubiquitin-ligase activity but no detectable kinase activity. RipV1 could trans- ubiquitinate RLCK-IXb-1 in vitro and promote its stability in planta. Using virus-induced gene silencing of RLCK-IXb homologs in Nicotiana benthamiana, we could further show that several RLCK-IXb proteins act as negative regulators of early PTI signaling. RipV1 was previously reported to contribute to R. solanacearum virulence in potato and to elicit cell death in an E3 ligase activity-dependent manner in N. benthamiana. Here we show that RipV1-induced cell death occurred in plants impaired for effector recognition but could be suppressed by over-expression of RLCK-IXb-1, suggesting that this response is related to the virulence function of RipV1. Altogether, our work identifies possible substrates of an NEL effector and underlines the complex roles of RLCKs in plant immune signaling.

plant biology↗

bioRxiv2025

The recognition of YopJ family effectors depends on ZAR1/JIM2 immune complex in Nicotiana benthamiana.

Pathogens deploy effector proteins to manipulate host physiology and promote infection. YopJ family effectors are highly conserved across bacterial genera that cause crop diseases. Nucleotide-binding leucine-rich repeat receptors (NLRs) play a central role in direct or indirect recognition of effectors and trigger immune responses, including hypersensitive cell death (HR). Two NLRs, Nicotiana benthamiana homologs of Pseudomonas tomato race 1 (NbPtr1) and HOPZ-ACTIVATED RESISTANCE 1 (NbZAR1) were recently identified as independently recognizing two YopJ family effectors, HopZ5 and AvrBsT/XopJ2. NbZAR1 also detects XopJ4 via the receptor-like cytoplasmic kinase XOPJ4 IMMUNITY 2 (JIM2). Here, we conducted Agrobacterium-mediated transient expression assays with 20 YopJ family effectors from five phytopathogenic bacterial genera and identified 12 YopJ family effectors that are recognized either by NbZAR1 or independently by NbZAR1 and NbPtr1. Furthermore, we show that YopJ family effector-induced HR was differentially suppressed by the deacetylase SUPPRESSOR OF AVRBST-ELICITED RESISTANCE 1, suggesting more than one mechanism for YopJ family effector recognition. This work provides the genetic basis of the recognition of YopJ family effectors in N. benthamiana and lays a foundation for the mechanistic study of NbZAR1/JIM2 and NbPtr1 mode of activation.

plant biology↗

bioRxiv2024

A bacterial type III effector hijacks plant ubiquitin proteases to evade degradation

Gram-negative bacterial pathogens inject effector proteins inside plant cells using a type III secretion system. These effectors manipulate plant cellular functions and suppress the plant immune system in order to promote bacterial proliferation. Despite the fact that bacterial effectors are exogenous threatening proteins potentially exposed to the protein degradation systems inside plant cells, effectors are relative stable and able to perform their virulence functions. In this work, we found that RipE1, an effector protein secreted by the bacterial wilt pathogen, Ralstonia solanacearum, undergoes phosphorylation of specific residues inside plant cells, and this promotes its stability. Moreover, RipE1 associates with plant ubiquitin proteases, which contribute to RipE1 deubiquitination and stabilization. The absence of those specific phosphorylation sites or specific host ubiquitin proteases leads to a substantial decrease in RipE1 protein accumulation, indicating that RipE1 hijacks plant post-translational modification regulators in order to promote its own stability. These results suggest that effector stability or degradation in plant cells constitute another molecular event subject to co-evolution between plants and pathogens.

plant biology↗

bioRxiv2023

The Ralstonia pseudosolanacearum effector RipE1 is recognized at the plasma membrane by NbPtr1, Nicotiana benthamiana homolog of Pseudomonas tomato race 1.

The bacterial wilt disease caused by soil-borne bacteria of the Ralstonia solanacearum species complex (RSSC) threatens important crops worldwide. Only a few immune receptors conferring resistance to this devastating disease are known so far. Individual RSSC strains deliver around 70 different type III secretion system effectors into host cells to manipulate the plant physiology and dampen immune responses. RipE1 is an effector conserved across RSSC isolated from diverse plant species and triggers immune responses in the model Solanaceae Nicotiana benthamiana. Here, we used multiplexed virus-induced gene silencing of the nucleotide-binding and leucine-rich repeat receptor family to identify the genetic basis of RipE1 recognition in N. benthamiana. Specific silencing of the N. benthamiana homolog of Solanum lycopersicoides Pseudomonas tomato race 1 gene (NbPtr1) completely abolished RipE1-induced hypersensitive response and immunity to Ralstonia pseudosolanacearum. In Nb-ptr1 knock-out plants, expression of the native NbPtr1 coding sequence was sufficient to restore RipE1 recognition. In addition to the putative catalytic triad Cys-His-Asp, RipE1 association with the host cell plasma membrane was found necessary for NbPtr1-dependent recognition. Furthermore, we found that NbPtr1-dependent recognition of RipE1 natural variants is polymorphic suggesting the coevolutionary nature of this interaction. This work hence provides an additional evidence for the indirect mode of activation of NbPtr1 and supports NbPtr1 relevance for resistance to bacterial wilt disease in Solanaceae.

plant biology↗

bioRxiv2022

Ptr1 and ZAR1 immune receptors confer overlapping and distinct bacterial pathogen effector specificities

Nucleotide-binding and leucine-rich repeat receptors (NLRs) detect pathogen effectors inside the plant cell. To identify Nicotiana benthamiana NLRs (NbNLRs) with novel effector recognition specificity, we designed an NbNLR VIGS library and conducted a rapid reverse genetic screen. During the NbNLR VIGS library screening, we identified that N. benthamiana homolog of Ptr1 (PSEUDOMONAS SYRINGAE PV. TOMATO RACE 1 RESISTANCE) recognizes the Pseudomonas effectors AvrRpt2, AvrRpm1, and AvrB. We demonstrated that recognition of the Xanthomonas effector AvrBsT and the Pseudomonas effector HopZ5 in N. benthamiana is conferred independently by N. benthamiana homolog of Ptr1 and ZAR1 (HOPZ-ACTIVATED RESISTANCE 1). In addition, we showed that the RLCK XII family protein JIM2 (XOPJ4 IMMUNITY 2) physically interacts with AvrBsT and HopZ5 and is required for the NbZAR1-dependent recognition of AvrBsT and HopZ5. The recognition of multiple bacterial effectors by Ptr1 and ZAR1 in N. benthamiana demonstrates a convergent evolution of effector recognition across plant species. Identification of key components involved in Ptr1 and ZAR1 mediated immunity would reveal unique mechanisms of expanded effector recognition and be useful for engineering resistance in solanaceous crops.

plant biology↗

bioRxiv2022

The Phytophthora capsici RxLR effector CRISIS2 has roles in suppression of PTI and triggering cell death in host plant

Pathogen effectors can suppress various plant immune responses, suggesting that they have multiple targets in the host. To understand the mechanisms underlying plasma membrane-associated and effector-mediated immunity, we performed Phytophthora capsici RxLR cell death Inducer Suppressing Immune System (CRISIS) screening. In Nicotiana benthamiana, the cell death induced by the RxLR effector CRISIS2 is inhibited by the irreversible plasma membrane H+-ATPase (PMA) activator fusicoccin. Biochemical and gene silencing analyses revealed that CRISIS2 physically and functionally associates with PMAs and induces host cell death independent of immune receptors. CRISIS2 induces apoplastic alkalization by suppressing PMA activity via its association with the C-terminal regulatory domain of PMA. In planta expression of CRISIS2 significantly enhanced the virulence of P. capsici, whereas host-induced gene silencing of CRISIS2 compromised disease symptom and biomass of P. capsici. Furthermore, co-immunoprecipitation assays revealed that CRISIS2 constitutively associates with BAK1, the co-receptor of pattern recognition receptors (PRRs). CRISIS2 interferes with the FLS2-BAK1 complex induced by flagellin perception and impairs downstream signaling from the PRR complex. Proteomics and gene silencing assays identified putative PRRs that negatively regulate the virulence of P. capsici in N. benthamiana as interactors of CRISIS2 and BAK1. Our study identified a novel RxLR effector playing multiple roles in the suppression of plant defense and induction of cell death to support the pathogen hemibiotrophic life cycle in the host plant.

plant biology↗