Pathogen Effectors Research Articles

The root-knot nematode effector Mi2G02 hijacks a host plant trihelix transcription factor to promote nematode parasitism

Root-knot nematodes (RKNs) cause huge agricultural losses every year. They secrete a repertoire of effectors to facilitate parasitism through the induction of plant-derived giant feeding cells, which serve as their sole source of nutrients. However, the mode of action of these effectors and their targeted host proteins remain largely unknown. In this study, we investigated the role of the effector Mi2G02 in Meloidogyne incognita parasitism. Host-derived Mi2G02 RNA interference in Arabidopsis thaliana affected giant cell development, whereas ectopic expression of Mi2G02 promoted root growth and increased plant susceptibility to M. incognita. We used various combinations of approaches to study the specific interactions between Mi2G02 and A. thaliana GT-3a, a trihelix transcription factor. GT-3a knockout in A. thaliana affected feeding-site development, resulting in production of fewer egg masses, whereas GT-3a overexpression in A. thaliana increased susceptibility to M. incognita and also root growth. Moreover, we demonstrated that Mi2G02 plays a role in maintaining GT-3a protein stabilization by inhibiting the 26S proteasome-dependent pathway, leading to suppression of TOZ and RAD23C expression and thus promoting nematode parasitism. This work enhances our understanding of how a pathogen effector manipulates the role and regulation of a transcription factor by interfering with a proteolysis pathway to reprogram gene expression for development of nematode feeding cells.

Expression profiling and characterization of key RGA involved in lentil Fusarium wilt Race 5 resistance.

Fusarium wilt is a major threat to lentil production in India and worldwide. The presence of evolving virulent races has imposed the necessity of reliable management practices including breeding for resistance using unexplored germplasms. The magnitude of resistance by the plant is determined by rapid recognition of the pathogen and induction of defence genes. Resistance gene analogues have been key factors involved in the recognition and induction of defence response. In the present study, the expression of key RGA previously cloned was determined in three resistant accessions (L65, L83 and L90) and a susceptible accession (L27). The expression was assessed via qPCR at 24, 48 and 72hpi against virulent race5 (CG-5). All the RGAs differentially transcribed in resistant and susceptible accession showed temporal variation. RGA Lc2, Lc8, Ln1 and Lo6 produced cDNA signals during early infection (24hpi) predicting its involvement in recognition. LoRGA6 showed significant upregulation in L65 and L83 while downregulating in L27 and the full length of LoRGA6 loci was isolated by 5' and 3' RACE PCR. In-silico characterization revealed LoRGA6 loci code for 912 amino acids long polypeptide with a TIR motif at the N terminal and eight LRR motifs at the C terminal. The tertiary structure revealed a concave pocket-like structure at the LRR domain potentially involved in pathogen effectors interaction. The loci have ADP binding domain and ATPase activity. This has further paved the path for functional analysis of the loci by VIGS to understand the molecular mechanism of resistance.

Plant immunity suppressor SKRP encodes a novel RNA-binding protein that targets exon 3' end of unspliced RNA.

The regulatory roles of RNA splicing in plant immunity are emerging but still largely obscure. We reported previously that Phytophthora pathogen effector Avr3c targets a soybean protein SKRP (serine/lysine/arginine-rich protein) to impair soybean basal immunity by regulating host pre-mRNA alternative splicing, while the biochemical nature of SKRP remains unknown. Here, by using Arabidopsis as a model, we studied the mechanism of SKRP in regulating pre-mRNA splicing and plant immunity. AtSKRP confers impaired plant immunity against Phytophthora capsici and associates with spliceosome component PRP8 and splicing factor SR45, which positively and negatively regulate plant immunity, respectively. Enhanced crosslinking and immunoprecipitation followed by high-throughput sequencing (eCLIP-seq) showed AtSKRP is a novel RNA-binding protein that targets exon 3' end of unspliced RNA. Such position-specific binding of SKRP is associated with its activity in suppressing intron retention, including at positive immune regulatory genes UBP25 and RAR1. In addition, we found AtSKRP self-interact and forms oligomer, and these properties are associated with its function in plant immunity. Overall, our findings reveal that the immune repressor SKRP is a spliceosome-associated protein that targets exon 3' end to regulate pre-mRNA splicing in Arabidopsis.

Solanum americanum genome-assisted discovery of immune receptors that detect potato late blight pathogen effectors

Potato (Solanum tuberosum) and tomato (Solanum lycopersicon) crops suffer severe losses to late blight caused by the oomycete pathogen Phytophthora infestans. Solanum americanum, a relative of potato and tomato, is globally distributed and most accessions are highly blight resistant. We generated high-quality reference genomes of four S. americanum accessions, resequenced 52 accessions, and defined a pan-NLRome of S. americanum immune receptor genes. We further screened for variation in recognition of 315P. infestans RXLR effectors in 52 S. americanum accessions. Using these genomic and phenotypic data, we cloned three NLR-encoding genes, Rpi-amr4, R02860 and R04373, that recognize cognate P. infestans RXLR effectors PITG_22825 (AVRamr4), PITG_02860 and PITG_04373. These genomic resources and methodologies will support efforts to engineer potatoes with durable late blight resistance and can be applied to diseases of other crops.

Interplay between cell-surface receptor and intracellular NLR-mediated immune responses.

The functional link between cell-surface receptors and intracellular NLR immune receptors is a critical aspect of plant immunity. To establish disease, successful pathogens have evolved mechanisms to suppress cell-surface immune signalling. In response, plants have adapted by evolving NLRs that recognize pathogen effectors involved in this suppression, thereby counteracting their immune-suppressing function. This ongoing co-evolutionary struggle has seemingly resulted in intertwined signalling pathways in some plant species, where NLRs form a separate signalling branch downstream of activated cell-surface receptor complexes essential for full immunity. Understanding these interconnected receptor networks could lead to novel strategies for developing durable disease resistance.

Dual functions of a novel effector in the plant and pathogen arms race

Ralstonia solanacearum is a soil-borne bacterium that causes bacterial wilt disease in over 250 plant species. It has been identified as one of the top ten most serious plant pathogenic bacteria globally, causing significant crop yield loss every year. Despite its large impact on agricultural economics, the molecular mechanisms underlying plant defense against Ralstonia infection and by which Ralstonia grows within the plant xylem remain largely unexplored. In a recent article, Ke et al. discovered a distinct pathogen effector, which acted as an immune elicitor in plants but also played dual roles in compromising plant immune activation and increasing nutrient acquisition from the host plants for pathogen propagation.

How to convert host plants into nonhosts.

Recent research demonstrates that undermining interactions between pathogen effectors and their host target proteins can reduce infection. As more effector-target pairs are identified, their structures and interaction surfaces exposed, and there is the possibility of making multiple edits to diverse plant genomes, the desire to convert crops to nonhosts could become reality.

From Gene-for-Gene to Resistosomes: Flor's Enduring Legacy.

The gene-for-gene model proposed by H. H. Flor has been one of the fundamental precepts of plant-pathogen interactions that has underpinned decades of research towards our current concepts of plant immunity. The broad validity of this model as an elegant and accurate genetic description of specific recognition events between the products of plant resistance (R) and pathogen avirulence (Avr) genes has been demonstrated many times over in a wide variety of plant disease systems. In recent years detailed molecular and structural analyses have provided a deep understanding of the principles by which plant immune receptors recognize pathogen effectors, including providing molecular descriptions of many of the genetic loci in flax and flax rust characterized by Flor. Recent advances in molecular and structural understanding of immune receptor recognition and activation mechanisms have brought the field to a new level, where rational design of novel receptors through engineering approaches is becoming a realizable goal. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Structural polymorphisms within a common powdery mildew effector scaffold as a driver of coevolution with cereal immune receptors

In plants, host-pathogen coevolution often manifests in reciprocal, adaptive genetic changes through variations in host nucleotide-binding leucine-rich repeat immune receptors (NLRs) and virulence-promoting pathogen effectors. In grass powdery mildew (PM) fungi, an extreme expansion of a RNase-like effector family, termed RALPH, dominates the effector repertoire, with some members recognized as avirulence (AVR) effectors by cereal NLR receptors. We report the structures of the sequence-unrelated barley PM effectors AVRA6, AVRA7, and allelic AVRA10/AVRA22 variants, which are detected by highly sequence-related barley NLRs MLA6, MLA7, MLA10, and MLA22 and of wheat PM AVRPM2 detected by the unrelated wheat NLR PM2. The AVR effectors adopt a common scaffold, which is shared with the RNase T1/F1 family. We found striking variations in the number, position, and length of individual structural elements between RALPH AVRs, which is associated with a differentiation of RALPH effector subfamilies. We show that all RALPH AVRs tested have lost nuclease and synthetase activities of the RNase T1/F1 family and lack significant binding to RNA, implying that their virulence activities are associated with neo-functionalization events. Structure-guided mutagenesis identified six AVRA6 residues that are sufficient to turn a sequence-diverged member of the same RALPH subfamily into an effector specifically detected by MLA6. Similar structure-guided information for AVRA10 and AVRA22 indicates that MLA receptors detect largely distinct effector surface patches. Thus, coupling of sequence and structural polymorphisms within the RALPH scaffold of PMs facilitated escape from NLR recognition and potential acquisition of diverse virulence functions.

Plasma membrane association and resistosome formation of plant helper immune receptors

Intracellular plant immune receptors, termed NLRs (Nucleotide-binding Leucine-rich repeat Receptors), confer effector-triggered immunity. Sensor NLRs are responsible for pathogen effector recognition. Helper NLRs function downstream of sensor NLRs to transduce signaling and induce cell death and immunity. Activation of sensor NLRs that contain TIR (Toll/interleukin-1receptor) domains generates small molecules that induce an association between a downstream heterodimer signalosome of EDS1 (EnhancedDisease Susceptibility 1)/SAG101 (Senescence-AssociatedGene 101) and the helper NLR of NRG1 (NRequired Gene 1). Autoactive NRG1s oligomerize and form calcium signaling channels largely localized at the plasma membrane (PM). The molecular mechanisms of helper NLR PM association and effector-induced NRG1 oligomerization are not well characterized. We demonstrate that helper NLRs require positively charged residues in their N-terminal domains for phospholipid binding and PM association before and after activation, despite oligomerization and conformational changes that accompany activation. We demonstrate that effector activation of a TIR-containing sensor NLR induces NRG1 oligomerization at the PM and that the cytoplasmic pool of EDS1/SAG101 is critical for cell death function. EDS1/SAG101 cannot be detected in the oligomerized NRG1 resistosome, suggesting that additional unknown triggers might be required to induce the dissociation of EDS1/SAG101 from the previously described NRG1/EDS1/SAG101 heterotrimer before subsequent NRG1 oligomerization. Alternatively, the conformational changes resulting from NRG1 oligomerization abrogate the interface for EDS1/SAG101 association. Our data provide observations regarding dynamic PM association during helper NLR activation and underpin an updated model for effector-induced NRG1 resistosome formation.

Differential CaKAN3-CaHSF8 associations underlie distinct immune and heat responses under high temperature and high humidity conditions

High temperature and high humidity (HTHH) conditions increase plant susceptibility to a variety of diseases, including bacterial wilt in solanaceous plants. Some solanaceous plant cultivars have evolved mechanisms to activate HTHH-specific immunity to cope with bacterial wilt disease. However, the underlying mechanisms remain poorly understood. Here we find that CaKAN3 and CaHSF8 upregulate and physically interact with each other in nuclei under HTHH conditions without inoculation or early after inoculation with R. solanacearum in pepper. Consequently, CaKAN3 and CaHSF8 synergistically confer immunity against R. solanacearum via activating a subset of NLRs which initiates immune signaling upon perception of unidentified pathogen effectors. Intriguingly, when HTHH conditions are prolonged without pathogen attack or the temperature goes higher, CaHSF8 no longer interacts with CaKAN3. Instead, it directly upregulates a subset of HSP genes thus activating thermotolerance. Our findings highlight mechanisms controlling context-specific activation of high-temperature-specific pepper immunity and thermotolerance mediated by differential CaKAN3-CaHSF8 associations.

An NLR Integrated Domain toolkit to identify plant pathogen effector targets.

Plant immune receptors, known as Nod-like Receptors (NLRs), possess unique integrated decoy domains that enable plants to attract pathogen effectors and initiate a specific immune response. The aim of this study was to create a library of these integrated domains (IDs) and screen them with pathogen effectors to identify new targets for effector virulence and NLR-effector interactions. This works compiles IDs found in NLRs from seven different plant species and produced a library of 78 plasmid clones containing a total of 104 IDs, representing 43 distinct Interpro domains. They conducted a yeast-two-hybrid assay, followed by an in planta interaction test, using 32 conserved effectors from Ralstonia pseudosolanacearum type III. Through these screenings, they discovered three interactions involving different IDs (kinase, DUF3542, WRKY) interacting with two unrelated type III effectors (RipAE and PopP2). Of particular interest was the interaction between PopP2 and ID#85, an atypical WRKY domain integrated into a soybean NLR gene (GmNLR-ID#85). Using a FRET-FLIM technique to detect protein-protein interactions in living plant cells, we demonstrated that PopP2 physically associates with ID#85 in the nucleus. However, unlike the known WRKY-containing Arabidopsis RRS1-R NLR receptor, GmNLR-ID#85 could not be acetylated by PopP2 and failed to activate RPS4-dependent immunity when introduced into the RRS1-R immune receptor. The generated library of 78 plasmid clones, encompassing these screenable IDs, is publicly available through Addgene. This resource is expected to be valuable for the scientific community in discovering new targets for effectors and potentially engineering novel plant immune receptors.

Allelic compatibility in plant immune receptors facilitates engineering of new effector recognition specificities.

Engineering the plant immune system offers genetic solutions to mitigate crop diseases caused by diverse agriculturally significant pathogens and pests. Modification of intracellular plant immune receptors of the nucleotide-binding leucine-rich repeat (NLR) receptor superfamily for expanded recognition of pathogen virulence proteins (effectors) is a promising approach for engineering disease resistance. However, engineering can cause NLR autoactivation, resulting in constitutive defense responses that are deleterious to the plant. This may be due to plant NLRs associating in highly complex signaling networks that coevolve together, and changes through breeding or genetic modification can generate incompatible combinations, resulting in autoimmune phenotypes. The sensor and helper NLRs of the rice (Oryza sativa) NLR pair Pik have coevolved, and mismatching between noncoevolved alleles triggers constitutive activation and cell death. This limits the extent to which protein modifications can be used to engineer pathogen recognition and enhance disease resistance mediated by these NLRs. Here, we dissected incompatibility determinants in the Pik pair in Nicotiana benthamiana and found that heavy metal-associated (HMA) domains integrated in Pik-1 not only evolved to bind pathogen effectors but also likely coevolved with other NLR domains to maintain immune homeostasis. This explains why changes in integrated domains can lead to autoactivation. We then used this knowledge to facilitate engineering of new effector recognition specificities, overcoming initial autoimmune penalties. We show that by mismatching alleles of the rice sensor and helper NLRs Pik-1 and Pik-2, we can enable the integration of synthetic domains with novel and enhanced recognition specificities. Taken together, our results reveal a strategy for engineering NLRs, which has the potential to allow an expanded set of integrations and therefore new disease resistance specificities in plants.

A dominant-negative avirulence effector of the barley powdery mildew fungus provides mechanistic insight into barley MLA immune receptor activation.

Nucleotide-binding leucine-rich repeat receptors (NLRs) recognize pathogen effectors to mediate plant disease resistance often involving host cell death. Effectors escape NLR recognition through polymorphisms, allowing the pathogen to proliferate on previously resistant host plants. The powdery mildew effector AVRA13-1 is recognized by the barley NLR MLA13 and activates host cell death. We demonstrate here that a virulent form of AVRA13, called AVRA13-V2, escapes MLA13 recognition by substituting a serine for a leucine residue at the C-terminus. Counterintuitively, this substitution in AVRA13-V2 resulted in an enhanced MLA13 association and prevented the detection of AVRA13-1 by MLA13. Therefore, AVRA13-V2 is a dominant-negative form of AVRA13 and has probably contributed to the breakdown of Mla13 resistance. Despite this dominant-negative activity, AVRA13-V2 failed to suppress host cell death mediated by the MLA13 autoactive MHD variant. Neither AVRA13-1 nor AVRA13-V2 interacted with the MLA13 autoactive variant, implying that the binding moiety in MLA13 that mediates association with AVRA13-1 is altered after receptor activation. We also show that mutations in the MLA13 coiled-coil domain, which were thought to impair Ca2+ channel activity and NLR function, instead resulted in MLA13 autoactive cell death. Our results constitute an important step to define intermediate receptor conformations during NLR activation.

Jurassic NLR: Conserved and dynamic evolutionary features of the atypically ancient immune receptor ZAR1.

Plant nucleotide-binding leucine-rich repeat (NLR) immune receptors generally exhibit hallmarks of rapid evolution, even at the intraspecific level. We used iterative sequence similarity searches coupled with phylogenetic analyses to reconstruct the evolutionary history of HOPZ-ACTIVATED RESISTANCE1 (ZAR1), an atypically conserved NLR that traces its origin to early flowering plant lineages ∼220 to 150 million yrs ago (Jurassic period). We discovered 120 ZAR1 orthologs in 88 species, including the monocot Colocasia esculenta, the magnoliid Cinnamomum micranthum, and most eudicots, notably the Ranunculales species Aquilegia coerulea, which is outside the core eudicots. Ortholog sequence analyses revealed highly conserved features of ZAR1, including regions for pathogen effector recognition and cell death activation. We functionally reconstructed the cell death activity of ZAR1 and its partner receptor-like cytoplasmic kinase (RLCK) from distantly related plant species, experimentally validating the hypothesis that ZAR1 evolved to partner with RLCKs early in its evolution. In addition, ZAR1 acquired novel molecular features. In cassava (Manihot esculenta) and cotton (Gossypium spp.), ZAR1 carries a C-terminal thioredoxin-like domain, and in several taxa, ZAR1 duplicated into 2 paralog families, which underwent distinct evolutionary paths. ZAR1 stands out among angiosperm NLR genes for having experienced relatively limited duplication and expansion throughout its deep evolutionary history. Nonetheless, ZAR1 also gave rise to noncanonical NLRs with integrated domains and degenerated molecular features.

NLRs derepress MED10b- and MED7-mediated repression of jasmonate-dependent transcription to activate immunity

Plant intracellular nucleotide-binding domain, leucine-rich repeat-containing receptors (NLRs) activate a robust immune response upon detection of pathogen effectors. How NLRs induce downstream immune defense genes remains poorly understood. The Mediator complex plays a central role in transducing signals from gene-specific transcription factors to the transcription machinery for gene transcription/activation. In this study, we demonstrate that MED10b and MED7 of the Mediator complex mediate jasmonate-dependent transcription repression, and coiled-coil NLRs (CNLs) in Solanaceae modulate MED10b/MED7 to activate immunity. Using the tomato CNL Sw-5b, which confers resistance to tospovirus, as a model, we found that the CC domain of Sw-5b directly interacts with MED10b. Knockout/down of MED10b and other subunits including MED7 of the middle module of Mediator activates plant defense against tospovirus. MED10b was found to directly interact with MED7, and MED7 directly interacts with JAZ proteins, which function as transcriptional repressors of jasmonic acid (JA) signaling. MED10b-MED7-JAZ together can strongly repress the expression of JA-responsive genes. The activated Sw-5b CC interferes with the interaction between MED10b and MED7, leading to the activation of JA-dependent defense signaling against tospovirus. Furthermore, we found that CC domains of various other CNLs including helper NLR NRCs from Solanaceae modulate MED10b/MED7 to activate defense against different pathogens. Together, our findings reveal that MED10b/MED7 serve as a previously unknown repressor of jasmonate-dependent transcription repression and are modulated by diverse CNLs in Solanaceae to activate the JA-specific defense pathways.

Altering specificity and auto-activity of plant immune receptors Sr33 and Sr50 via a rational engineering approach.

Many resistance genes deployed against pathogens in crops are intracellular nucleotide-binding leucine-rich repeat receptors (NLRs). The ability to rationally engineer the specificity of NLRs will be crucial in the response to newly emerging crop diseases. Successful attempts to modify NLR recognition have been limited to untargeted approaches or depended on previously available structural information or knowledge of pathogen-effector targets. However, this information is not available for most NLR-effector pairs. Here, we demonstrate the precise prediction and subsequent transfer of residues involved in effector recognition between two closely related NLRs without their experimentally determined structure or detailed knowledge about their pathogen effector targets. By combining phylogenetics, allele diversity analysis, and structural modeling, we successfully predicted residues mediating interaction of Sr50 with its cognate effector AvrSr50 and transferred Sr50's recognition specificity to the closely related NLR Sr33. We created synthetic versions of Sr33 that contain amino acids from Sr50, including Sr33syn that gained the ability to recognize AvrSr50 with 12 amino acid substitutions. Furthermore, we discovered that sites in the leucine rich-repeat domain needed to transfer recognition specificity to Sr33 also influence auto-activity in Sr50. Structural modeling suggests these residues interact with a part of the NB-ARC domain, which we named the NB-ARC latch, to possibly maintain the inactive state of the receptor. Our approach demonstrates rational modifications of NLRs, which could be useful to enhance existing elite crop germplasm.

Structural mechanism of heavy metal-associated integrated domain engineering of paired nucleotide-binding and leucine-rich repeat proteins in rice.

Plant nucleotide-binding and leucine-rich repeat (NLR) proteins are immune sensors that detect pathogen effectors and initiate a strong immune response. In many cases, single NLR proteins are sufficient for both effector recognition and signaling activation. These proteins possess a conserved architecture, including a C-terminal leucine-rich repeat (LRR) domain, a central nucleotide-binding (NB) domain, and a variable N-terminal domain. Nevertheless, many paired NLRs linked in a head-to-head configuration have now been identified. The ones carrying integrated domains (IDs) can recognize pathogen effector proteins by various modes; these are known as sensor NLR (sNLR) proteins. Structural and biochemical studies have provided insights into the molecular basis of heavy metal-associated IDs (HMA IDs) from paired NLRs in rice and revealed the co-evolution between pathogens and hosts by combining naturally occurring favorable interactions across diverse interfaces. Focusing on structural and molecular models, here we highlight advances in structure-guided engineering to expand and enhance the response profile of paired NLR-HMA IDs in rice to variants of the rice blast pathogen MAX-effectors (Magnaporthe oryzae AVRs and ToxB-like). These results demonstrate that the HMA IDs-based design of rice materials with broad and enhanced resistance profiles possesses great application potential but also face considerable challenges.

Defining the Roles of Pyruvate Oxidation, TCA Cycle, and Mannitol Metabolism in Methicillin-Resistant Staphylococcus aureus Catheter-Associated Urinary Tract Infection.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of complicated urinary tract infection (UTI) associated with the use of indwelling urinary catheters. Previous reports have revealed host and pathogen effectors critical for MRSA uropathogenesis. Here, we sought to determine the significance of specific metabolic pathways during MRSA UTI. First, we identified four mutants from the Nebraska transposon mutant library in the MRSA JE2 background that grew normally in rich medium but displayed significantly reduced growth in pooled human urine (HU). This prompted us to transduce the uropathogenic MRSA 1369 strain with the transposon mutants in sucD and fumC (tricarboxylic acid [TCA] cycle), mtlD (mannitol metabolism), and lpdA (pyruvate oxidation). Notably, sucD, fumC, and mtlD were also significantly upregulated in the MRSA 1369 strain upon exposure to HU. Compared to the WT, the MRSA 1369 lpdA mutant was significantly defective for (i) growth in HU, and (ii) colonization of the urinary tract and dissemination to the kidneys and the spleen in the mouse model of catheter-associated UTI (CAUTI), which may be attributed to its increased membrane hydrophobicity and higher susceptibility to killing by human blood. In contrast to their counterparts in the JE2 background, the sucD, fumC, and mtlD mutants in the MRSA 1369 background grew normally in HU; however, they displayed significant fitness defects in the CAUTI mouse model. Overall, identification of novel metabolic pathways important for the urinary fitness and survival of MRSA can be used for the development of novel therapeutics. IMPORTANCE While Staphylococcus aureus has historically not been considered a uropathogen, S. aureus urinary tract infection (UTI) is clinically significant in certain patient populations, including those with chronic indwelling urinary catheters. Moreover, most S. aureus strains causing catheter-associated UTI (CAUTI) are methicillin-resistant S. aureus (MRSA). MRSA is difficult to treat due to limited treatment options and the potential to deteriorate into life-threatening bacteremia, urosepsis, and shock. In this study, we found that pathways involved in pyruvate oxidation, TCA cycle, and mannitol metabolism are important for MRSA fitness and survival in the urinary tract. Improved understanding of the metabolic needs of MRSA in the urinary tract may help us develop novel inhibitors of MRSA metabolism that can be used to treat MRSA-CAUTI more effectively.

Genome engineering of disease susceptibility genes for enhancing resistance in plants.

Introgression of disease resistance genes (R-genes) to fight against an array of phytopathogens takes several years using conventional breeding approaches. Pathogens develop mechanism(s) to escape plants immune system by evolving new strains/races, thus making them susceptible to disease. Conversely, disruption of host susceptibility factors (or S-genes) provides opportunities for resistance breeding in crops. S-genes are often exploited by phytopathogens to promote their growth and infection. Therefore, identification and targeting of disease susceptibility genes (S-genes) are gaining more attention for the acquisition of resistance in plants. Genome engineering of S-genes results in targeted, transgene-free gene modification through CRISPR-Cas-mediated technology and has been reported in several agriculturally important crops. In this review, we discuss the defense mechanism in plants against phytopathogens, tug of war between R-genes and S-genes, in silico techniques for identification of host-target (S-) genes and pathogen effector molecule(s), CRISPR-Cas-mediated S-gene engineering, its applications, challenges, and future prospects.