Chitin Elicitor Receptor Kinase Research Articles

The LYSIN MOTIF-CONTAINING RECEPTOR-LIKE KINASE 1 protein of banana is required for perception of pathogenic and symbiotic signals.

How plants can distinguish pathogenic and symbiotic fungi remains largely unknown. Here, we characterized the role of MaLYK1, a lysin motif receptor kinase of banana. Live cell imaging techniques were used in localization studies. RNA interference (RNAi)-silenced transgenic banana plants were generated to analyze the biological role of MaLYK1. The MaLYK1 ectodomain, chitin beads, chitooligosaccharides (COs) and mycorrhizal lipochitooligosaccharides (Myc-LCOs) were used in pulldown assays. Ligand-induced MaLYK1 complex formation was tested in immunoprecipitation experiments. Chimeric receptors were expressed in Lotus japonicus to characterize the function of the MaLYK1 kinase domain. MaLYK1 was localized to the plasma membrane. MaLYK1 expression was induced by Foc4 (Fusarium oxysporumf. sp.cubense race 4) and diverse microbe-associated molecular patterns. MaLYK1-silenced banana lines showed reduced chitin-triggered defense responses, increased Foc4-induced disease symptoms and reduced mycorrhization. The MaLYK1 ectodomain was pulled down by chitin beads and LCOs or COs impaired this process. Ligand treatments induced MaLYK1 complex formation in planta. The kinase domain of MaLYK1 could functionally replace that of the chitin elicitor receptor kinase 1 (AtCERK1) in Arabidopsis thaliana and of a rhizobial LCO (Nod factor) receptor (LjNFR1) in L.japonicus. MaLYK1 represents a central molecular switch that controls defense- and symbiosis-related signaling.

Identification of Candidate Ergosterol-Responsive Proteins Associated with the Plasma Membrane of Arabidopsis thaliana.

The impact of fungal diseases on crop production negatively reflects on sustainable food production and overall economic health. Ergosterol is the major sterol component in fungal membranes and regarded as a general elicitor or microbe-associated molecular pattern (MAMP) molecule. Although plant responses to ergosterol have been reported, the perception mechanism is still unknown. Here, Arabidopsis thaliana protein fractions were used to identify those differentially regulated following ergosterol treatment; additionally, they were subjected to affinity-based chromatography enrichment strategies to capture and categorize ergosterol-interacting candidate proteins using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Mature plants were treated with 250 nM ergosterol over a 24 h period, and plasma membrane-associated fractions were isolated. In addition, ergosterol was immobilized on two different affinity-based systems to capture interacting proteins/complexes. This resulted in the identification of defense-related proteins such as chitin elicitor receptor kinase (CERK), non-race specific disease resistance/harpin-induced (NDR1/HIN1)-like protein, Ras-related proteins, aquaporins, remorin protein, leucine-rich repeat (LRR)- receptor like kinases (RLKs), G-type lectin S-receptor-like serine/threonine-protein kinase (GsSRK), and glycosylphosphatidylinositol (GPI)-anchored protein. Furthermore, the results elucidated unknown signaling responses to this MAMP, including endocytosis, and other similarities to those previously reported for bacterial flagellin, lipopolysaccharides, and fungal chitin.

The effect of low and high molecular weight chitosan on the control of gray mold (Botrytis cinerea) on kiwifruit and host response

The inhibitory effect of low (LMWC, 3.4–51.3 kDa) and high molecular weight chitosan (HMWC, 136.8–342.0 kDa) on gray mold (Botrytis cinerea) of kiwifruit was evaluated. Results indicated that both LMWC and HMWC significantly inhibited the development of gray mold, with LMWC having a greater inhibitory effect than HMWC. LMWC, was more effective than HMWC in inhibiting spore germination and mycelial growth of B. cinerea. LMWC also induced the accumulation of higher levels of hydrogen peroxide (H2O2), and greater level of activity of several defense-related enzymes. Moreover, LMWC had a greater ability than HMWC to penetrate the cell walls in kiwifruit epidermal peel tissue. While the expression of chitin elicitor receptor kinase 1 (CERK1), mitogen-activated protein kinase (MPK3), PR1, and PR5 were significantly induced in kiwifruit by both LMWC and HMWC, the level of induction of CERK1 and PR5 was more highly induced by LMWC. Collectively, the results indicate that LMWC is more effective than HMWC in inhibiting gray mold of kiwifruit, most likely due to the ability of LMWC to more readily penetrate the epidermal cell walls of kiwifruit and activate a greater defense response.

MAMP-triggered plant immunity mediated by the LysM-receptor kinase CERK1

Lysin motif (LysM) receptor-like proteins/kinases (LysM-RLPs/RLKs) are well known to play an important role in the induction of defense or symbiosis signaling through the recognition of carbohydrate ligands in plants. Chitin elicitor receptor kinase 1 (CERK1) is the receptor-like kinase (RLK) essential for chitin-induced defense signaling in Arabidopsis and rice. At/OsCERK1 is also known to be important for peptidoglycan (PGN)-induced defense signaling. To induce chitin and PGN responses, CERK1 forms a receptor complex with corresponding LysM-type receptors such as CEBiP, LYM1/3 or LYP4/6. Furthermore, OsCERK1 in rice also plays a key role in lipopolysaccharide (LPS) signaling, and AtCERK1 in Arabidopsis is involved in unbranched β-glucan signaling. In any case, CERK1 plays a crucial role in the activation of defense signaling by these ligands and is an essential hub-RLK/co-receptor in these systems. After chitin perception, autophosphorylation of the CERK1 kinase domain is essential for inducing immune signaling, and some functionally important phosphorylation sites have been identified. In addition, several CERK1-interacting proteins and their contribution to the downstream signaling have been reported. In particular, phosphorylation of receptor-like cytoplasmic kinases (RLCKs) by CERK1 is important for the activation of chitin signaling. These findings have contributed to our understanding of the early steps of chitin signaling. This review focuses on current knowledge about CERK1-mediated receptor complex formation and subsequent intracellular signaling.

The grapevine (Vitis vinifera) LysM receptor kinases VvLYK1-1 and VvLYK1-2 mediate chitooligosaccharide-triggered immunity.

SummaryChitin, a major component of fungal cell walls, is a well‐known pathogen‐associated molecular pattern (PAMP) that triggers defense responses in several mammal and plant species. Here, we show that two chitooligosaccharides, chitin and chitosan, act as PAMPs in grapevine (Vitis vinifera) as they elicit immune signalling events, defense gene expression and resistance against fungal diseases. To identify their cognate receptors, the grapevine family of LysM receptor kinases (LysM‐RKs) was annotated and their gene expression profiles were characterized. Phylogenetic analysis clearly distinguished three V. vinifera LysM‐RKs (VvLYKs) located in the same clade as the Arabidopsis CHITIN ELICITOR RECEPTOR KINASE1 (AtCERK1), which mediates chitin‐induced immune responses. The Arabidopsis mutant Atcerk1, impaired in chitin perception, was transformed with these three putative orthologous genes encoding VvLYK1‐1, ‐2, or ‐3 to determine if they would complement the loss of AtCERK1 function. Our results provide evidence that VvLYK1‐1 and VvLYK1‐2, but not VvLYK1‐3, functionally complement the Atcerk1 mutant by restoring chitooligosaccharide‐induced MAPK activation and immune gene expression. Moreover, expression of VvLYK1‐1 in Atcerk1 restored penetration resistance to the non‐adapted grapevine powdery mildew (Erysiphe necator). On the whole, our results indicate that the grapevine VvLYK1‐1 and VvLYK1‐2 participate in chitin‐ and chitosan‐triggered immunity and that VvLYK1‐1 plays an important role in basal resistance against E. necator.

LysM1 in MmLYK2 is a motif required for the interaction of MmLYP1 and MmLYK2 in the chitin signaling.

Two LysM-containing proteins, namely, MmLYP1 and MmLYK2, were identified in mulberry. These proteins might be involved in chitin signaling. The LysM1 of MmLYK2 is critical for their interactions. Chitin is a major component of fungal cell walls and acts as an elicitor in plant innate immunity. Lysin motif (LysM)-containing proteins are essential for chitin recognition. However, related studies have been rarely reported in woody plants. In this study, in mulberry, the expression of a LysM-containing protein, MmLYP1, was significantly up-regulated after treatment with chitin and pathogenic fungi. In addition, MmLYP1 has an affinity for insoluble chitin polymers. Thus, MmLYP1 might function in chitin signaling. Since MmLYP1 lacks an intracellular domain, additional protein kinases are required for this signaling. An LysM-containing kinase, MmLYK2, was then identified. Expression of the MmLYK2 did not change significantly after chitin treatment, and the affinity of MmLYK2 for insoluble chitin was not high. The structure of MmLYP1 is similar to that of the chitin elicitor-binding proteins in rice and Arabidopsis. However, MmLYK2 has two LysM motifs, while the chitin elicitor receptor kinase 1 proteins in rice and Arabidopsis have one and three LysM motifs, respectively. The LysM1 of MmLYK2 interacted with all four LysM motifs in MmLYP1 and MmLYK2 in yeast. The chimera lacking the LysM1 of MmLYK2 did not interact with MmLYP1 and MmLYK2 in yeast and Nicotiana benthamiana cells. The LysM1 in MmLYK2 is the key motif in the interaction between MmLYP1 and MmLYK2, which may be involved in chitin signaling.

RNA-Seq transcriptome analysis of Amaranthus palmeri with differential tolerance to glufosinate herbicide.

Amaranthus palmeri (Amaranthaceae) is a noxious weed in several agroecosystems and in some cases seriously threatens the sustainability of crop production in North America. Glyphosate-resistant Amaranthus species are widespread, prompting the use of alternatives to glyphosate such as glufosinate, in conjunction with glufosinate-resistant crop cultivars, to help control glyphosate-resistant weeds. An experiment was conducted to analyze the transcriptome of A. palmeri plants that survived exposure to 0.55 kg ha-1 glufosinate. Since there was no record of glufosinate use at the collection site, survival of plants within the population are likely due to genetic expression that pre-dates selection; in the formal parlance of weed science this is described as natural tolerance. Leaf tissues from glufosinate-treated and non-treated seedlings were harvested 24 h after treatment (HAT) for RNA-Seq analysis. Global gene expression was measured using Illumina DNA sequence reads from non-treated and treated surviving (presumably tolerant, T) and susceptible (S) plants. The same plants were used to determine the mechanisms conferring differential tolerance to glufosinate. The S plants accumulated twice as much ammonia as did the T plants, 24 HAT. The relative copy number of the glufosinate target gene GS2 did not differ between T and S plants, with 1 to 3 GS2 copies in both biotypes. A reference cDNA transcriptome consisting of 72,780 contigs was assembled, with 65,282 sequences putatively annotated. Sequences of GS2 from the transcriptome assembly did not have polymorphisms unique to the tolerant plants. Five hundred sixty-seven genes were differentially expressed between treated T and S plants. Of the upregulated genes in treated T plants, 210 were more highly induced than were the upregulated genes in the treated S plants. Glufosinate-tolerant plants had greater induction of ABC transporter, glutathione S-transferase (GST), NAC transcription factor, nitronate monooxygenase (NMO), chitin elicitor receptor kinase (CERK1), heat shock protein 83, ethylene transcription factor, heat stress transcription factor, NADH-ubiquinone oxidoreductase, ABA 8’-hydroxylase, and cytochrome P450 genes (CYP72A, CYP94A1). Seven candidate genes were selected for validation using quantitative real time-PCR. While GST was upregulated in treated tolerant plants in at least one population, CYP72A219 was consistently highly expressed in all treated tolerant biotypes. These genes are candidates for contributing tolerance to glufosinate. Taken together, these results show that differential induction of stress-protection genes in a population can enable some individuals to survive herbicide application. Elevated expression of detoxification-related genes can get fixed in a population with sustained selection pressure, leading to evolution of resistance. Alternatively, sustained selection pressure could select for mutation(s) in the GS2 gene with the same consequence.

Functional characterization of an apple (Malus x domestica) LysM domain receptor encoding gene for its role in defense response

Apple gene, MD09G1111800, was identified as a chitin binding receptor-like kinase based on sequence similarity to AtCERK1 (chitin elicitor receptor kinase 1) from Arabidopsis. Sequence analysis on genomic structure, domain composition and transcriptional response to exogenous chitin treatment indicated that MD09G1111800 is an ortholog to AtCERK1 and was therefore named as MdCERK1. Tissue specific expression patterns indicated that MdCERK1 is primarily functional in vegetative tissues of leaf and root, rather than flower, fruit and seed of apple plant. The transcriptional regulation patterns in response to infection by Rhizoctonia solani demonstrated that MdCERK1 is a functional pattern recognition receptor protein (PRR) in apple root tissues. The ability of purified GST-MdCERK1 fusion protein to bind chitin molecules added biochemical evidence for its role in chitin mediated immune responses. An untargeted proteomic approach was also employed for identifying its putative in vivo interaction partners in apple root cells, and results indicated the existence of a functional receptor complex. These data support the conclusion that MdCERK1 is a chitin binding receptor kinase functioning in apple vegetative tissues, which plays an important role in defense activation in response to pathogen infection.

A Tyrosine Phosphorylation Cycle Regulates Fungal Activation of a Plant Receptor Ser/Thr Kinase

Plants initiate immunity by cell-surface pattern-recognition receptors (PRRs), which perceive non-self molecules. PRRs are predominantly receptor serine/threonine (Ser/Thr) kinases that are evolutionarily related to animal interleukin-1 receptor-associated kinase (IRAK)/Pelle-soluble kinases. However, how the activity of these receptor kinases is modulated remains poorly understood. We report that the Arabidopsis PRR chitin elicitor receptor kinase 1 (CERK1) is autophosphorylated in unstimulated cells at tyrosine428 (Tyr428), a modification that is required for CERK1 activation upon binding to the fungal cell wall component chitin. Upon chitin activation, CERK1 recruits the CERK1-interacting protein phosphatase 1 (CIPP1), a predicted Ser/Thr phosphatase, to dephosphorylate Tyr428 and dampen CERK1 signaling. CIPP1 subsequently dissociates from Tyr428-dephosphorylated CERK1, allowing CERK1 to regain Tyr428 autophosphorylation and return to a standby state. This work sheds light onto plant chitin signaling and shows that a receptor kinase and phosphatase can coordinately regulate signal transduction of a receptor kinase through a phosphorylation cycle.

Receptor-Like Kinase LYK9 in Pisum sativum L. Is the CERK1-Like Receptor that Controls Both Plant Immunity and AM Symbiosis Development.

Plants are able to discriminate and respond to structurally related chitooligosaccharide (CO) signals from pathogenic and symbiotic fungi. In model plants Arabidopsis thaliana and Oryza sativa LysM-receptor like kinases (LysM-RLK) AtCERK1 and OsCERK1 (chitin elicitor receptor kinase 1) were shown to be involved in response to CO signals. Based on phylogenetic analysis, the pea Pisum sativum L. LysM-RLK PsLYK9 was chosen as a possible candidate given its role on the CERK1-like receptor. The knockdown regulation of the PsLyk9 gene by RNA interference led to increased susceptibility to fungal pathogen Fusarium culmorum. Transcript levels of PsPAL2, PsPR10 defense-response genes were significantly reduced in PsLyk9 RNAi roots. PsLYK9’s involvement in recognizing short-chain COs as most numerous signals of arbuscular mycorrhizal (AM) fungi, was also evaluated. In transgenic roots with PsLyk9 knockdown treated with short-chain CO5, downregulation of AM symbiosis marker genes (PsDELLA3, PsNSP2, PsDWARF27) was observed. These results clearly indicate that PsLYK9 appears to be involved in the perception of COs and subsequent signal transduction in pea roots. It allows us to conclude that PsLYK9 is the most likely CERK1-like receptor in pea to be involved in the control of plant immunity and AM symbiosis formation.

Independent signalling cues underpin arbuscular mycorrhizal symbiosis and large lateral root induction in rice.

Perception of arbuscular mycorrhizal fungi (AMF) triggers distinct plant signalling responses for parallel establishment of symbiosis and induction of lateral root formation. Rice receptor kinase CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1) and α/β-fold hydrolase DWARF14-LIKE (D14L) are involved in pre-symbiotic fungal perception. After 6wk post-inoculation with Rhizophagus irregularis, root developmental responses, fungal colonization and transcriptional responses were monitored in two independent cerk1 null mutants; a deletion mutant lacking D14L, and with D14L complemented as well as their respective wild-type cultivars (cv Nipponbare and Nihonmasari). Here we show that although essential for symbiosis, D14L is dispensable for AMF-induced root architectural modulation, which conversely relies on CERK1. Our results demonstrate uncoupling of symbiosis and the symbiotic root developmental signalling during pre-symbiosis with CERK1 required for AMF-induced root architectural changes.

Defense Against Pathogens: Structural Insights into the Mechanism of Chitin Induced Activation of Innate Immunity.

Pattern recognition receptors on the plant cell surface mediate the recognition of microbe-associated molecular patterns, in a process which activates downstream immune signaling. These receptors are plasma membrane-localized kinases which need to be autophosphorylated to activate downstream responses. Perception of attacks from fungi occurs through recognition of chitin, a polymer of an N-acetylglucosamine which is a characteristic component of the cell walls of fungi. This process is regulated in Arabidopsis by chitin elicitor receptor kinase CERK1. A more complex process characterizes rice, in which regulation of chitin perception is operated by a complex composed of OsCERK1, a homolog of CERK1, and the chitin elicitor binding protein OsCEBiP. Recent literature has provided a mechanistic description of the complex regulation of activation of innate immunity in rice and an advance in the structural description of molecular players involved in this process. This review describes the current status of the understanding of molecular events involved in innate immunity activation in rice.

Transcriptome profiling and digital gene expression analysis of sweet potato for the identification of putative genes involved in the defense response against Fusarium oxysporum f. sp. batatas.

Sweet potato production is constrained by Fusarium wilt, which is caused by Fusarium oxysporum f. sp. batatas (Fob). The identification of genes related to disease resistance and the underlying mechanisms will contribute to improving disease resistance via sweet potato breeding programs. In the present study, we performed de novo transcriptome assembly and digital gene expression (DGE) profiling of sweet potato challenged with Fob using Illumina HiSeq technology. In total, 89,944,188 clean reads were generated from 12 samples and assembled into 101,988 unigenes with an average length of 666 bp; of these unigenes, 62,605 (61.38%) were functionally annotated in the NCBI non-redundant protein database by BLASTX with a cutoff E-value of 10−5. Clusters of Orthologous Groups (COG), Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations were examined to explore the unigenes’ functions. We constructed four DGE libraries for the sweet potato cultivars JinShan57 (JS57, highly resistant) and XinZhongHua (XZH, highly susceptible), which were challenged with pathogenic Fob. Genes that were differentially expressed in the four libraries were identified by comparing the transcriptomes. Various genes that were differentially expressed during defense, including chitin elicitor receptor kinase 1 (CERK), mitogen-activated protein kinase (MAPK), WRKY, NAC, MYB, and ethylene-responsive transcription factor (ERF), as well as resistance genes, pathogenesis-related genes, and genes involved in salicylic acid (SA) and jasmonic acid (JA) signaling pathways, were identified. These data represent a sequence resource for genetic and genomic studies of sweet potato that will enhance the understanding of the mechanism of disease resistance.

DArTseq molecular markers for resistance to Phytophthora cinnamomi in pineapple (Ananas comosus L.)

Root rot caused by Phytophthora cinnamomi is a major disease of pineapple worldwide, and while genetic resistance is known to exist within the genus, there have been few efforts to incorporate resistance into commercial varieties. The development of molecular markers and a better understanding of the physiology contributing to resistance would be a major advantage for breeding efforts. DArTseq was used in this study to investigate resistance to P. cinnamomi in pineapple. Resistance appears closely associated with a single broad loci on chromosome five covering the positions 4.6–5.5 Mb and two separate scaffolds. Thirteen putative resistance/susceptibility proteins were identified including six leucine-rich repeat receptor kinases, a chitin elicitor receptor kinase, a 2, 3-bisphosphoglycerate-dependent phosphoglycerate mutase, a microrchidia 4-like protein, a hypothetical protein, an uncharacterised protein family 0664 stress-induced protein, a transcription factor bHLH and a ribonuclease 2. The DArTseq bulk segregate approach successfully identified molecular markers associated with resistance to P. cinnamomi in pineapple.

Chitin-induced and CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) phosphorylation-dependent endocytosis of Arabidopsis thaliana LYSIN MOTIF-CONTAINING RECEPTOR-LIKE KINASE5 (LYK5).

To detect potential pathogens, plants perceive the fungal polysaccharide chitin through receptor complexes containing lysin motif receptor-like kinases (LysM-RLKs). To investigate the ligand-induced spatial dynamics of chitin receptor components, we studied the subcellular behaviour of two Arabidopsis thaliana LysM-RLKs involved in chitin signalling, CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) and LYSIN MOTIF-CONTAINING RECEPTOR-LIKE KINASE5. We performed standard and quantitative confocal laser scanning microscopy on stably transformed A. thaliana plants expressing fluorescently tagged CERK1 and LYK5 from their native promoters. Microscopy approaches were complemented by biochemical analyses in plants and invitro. Both CERK1 and LYK5 localized to the plasma membrane and showed constitutive endomembrane trafficking. After chitin treatment, however, CERK1 remained at the plasma membrane while LYK5 relocalized into mobile intracellular vesicles. Detailed analyses revealed that chitin perception transiently induced the internalization of LYK5 into late endocytic compartments. Plants that lacked CERK1 or expressed an enzymatically inactive CERK1 variant did not exhibit chitin-induced endocytosis of LYK5. CERK1 could phosphorylate LYK5 invitro and chitin treatment induced CERK1-dependent phosphorylation of LYK5 in planta. Our results suggest that chitin-induced phosphorylation by CERK1 triggers LYK5 internalization. Thus, our work identifies phosphorylation as a key regulatory step in endocytosis of plant RLKs and also provides evidence for receptor complex dissociation after ligand perception.

Nucleoporin NUP88/MOS7 is required for manifestation of phenotypes associated with the Arabidopsis CHITIN ELICITOR RECEPTOR KINASE1 mutant cerk1–4

ABSTRACTArabidopsis nucleoporin MOS7/NUP88 was identified in a forward-genetic screen for components that contribute to auto-immunity of the deregulated Resistance (R) gene mutant snc1, and is required for immunity to biotrophic and hemi-biotrophic pathogens. In a recent study, we showed that MOS7 is also essential to mount a full defense response against the necrotrophic fungal pathogen Botrytis cinerea, suggesting that MOS7 modulates plant defense responses to different types of pathogenic microbes. Here, we extend our analyses of MOS7-dependent plant immune responses and report the genetic requirement of MOS7 for manifestation of phenotypes associated with the CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) mutant cerk1–4.

Arabidopsis E3 ubiquitin ligase PLANT U‐BOX13 (PUB13) regulates chitin receptor LYSIN MOTIF RECEPTOR KINASE5 (LYK5) protein abundance

Long-chain chitooligosaccharides are fungal microbe-associated molecular patterns (MAMPs) that are recognized by LYSIN MOTIF RECEPTOR KINASE5 (LYK5), inducing the formation of a complex with CHITIN ELICITOR RECEPTOR KINASE1 (CERK1). Formation of this complex leads to activation of the CERK1 intracellular kinase domain and induction of plant innate immunity in Arabidopsis. We found that addition of chitooctaose induced LYK5 protein accumulation as a result of de novo gene expression and the inhibition of LYK5 protein degradation. Screening the putative E3 ligases for interaction with LYK5 identified PLANT U-BOX13 (PUB13), which complexed with LYK5, but this complex dissociated upon addition of chitooctaose. Consistent with these results, LYK5 protein abundance was higher in pub13 mutants compared with the wild type without chitooctaose treatment, while similar abundance was detected with the addition of chitooctaose. The pub13 mutants showed hypersensitivity to chitooctaose-induced rapid responses, such as the production of reactive oxygen species (ROS) and mitogen-activated protein (MAP) kinase phosphorylation, but exhibited normal responses to subsequent long-term chitooctaose treatment, such as gene expression and callose deposition. In addition, PUB13 could ubiquitinate the LYK5 kinase domain invitro. Taken together, our results suggest an important regulatory function for the turnover of LYK5 mediated by the E3 ligase PUB13.

Chitin receptor CERK1 links salt stress and chitin-triggered innate immunity in Arabidopsis.

In nature, plants need to respond to multiple environmental stresses that require the involvement and fine-tuning of different stress signaling pathways. Cross-tolerance, in which plants pre-treated with chitin (a fungal microbe-associated molecular pattern) have improved salt tolerance, was observed in Arabidopsis, but is not well understood. Here, we show a unique link between chitin and salt signaling mediated by the chitin receptor CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1). Transcriptome analysis revealed that salt stress-induced genes are highly correlated with chitin-induced genes, although this was not observed with other microbe-associated molecular patterns (MAMPs) or with other abiotic stresses. The cerk1 mutant was more susceptible to NaCl than was the wild type. cerk1 plants had an irregular increase of cytosolic calcium ([Ca2+ ]cyt ) after NaCl treatment. Bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation experiments indicated that CERK1 physically interacts with ANNEXIN 1 (ANN1), which was reported to form a calcium-permeable channel that contributes to the NaCl-induced [Ca2+ ]cyt signal. In turn, ann1 mutants showed elevated chitin-induced rapid responses. In short, molecular components previously shown to function in chitin or salt signaling physically interact and intimately link the downstream responses to fungal attack and salt stress.

Metabolo-transcriptome profiling of barley reveals induction of chitin elicitor receptor kinase gene (HvCERK1) conferring resistance against Fusarium graminearum

We report plausible disease resistance mechanisms induced by barley resistant genotype CI89831 against Fusarium head blight (FHB) based on metabolo-transcriptomics approach. We identified HvCERK1 as a candidate gene for FHB resistance, which is functional in resistant genotype CI9831 but non-functional in susceptible cultivars H106-371 and Zhedar-2. For the first time, we were able to show a hierarchy of regulatory genes that regulated downstream biosynthetic genes that eventually produced resistance related metabolites that reinforce the cell walls to contain the pathogen progress in plant. The HvCERK1 can be used for replacing in susceptible commercial cultivars, if non-functional, based on genome editing. Fusarium head blight (FHB) management is a great challenge in barley and wheat production worldwide. Though barley genome sequence and advanced omics technologies are available, till date none of the resistance mechanisms has been clearly deciphered. Hence, this study was aimed at identifying candidate gene(s) and elucidating resistance mechanisms induced by barley resistant genotype CI9831 based on integrated metabolomics and transcriptomics approach. Following Fusarium graminearum infection, we identified accumulation of specific set of induced secondary metabolites, belonging to phenylpropanoid, hydroxycinnamic acid (HCAA) and jasmonic acid pathways, and their biosynthetic genes. In association with these, receptor kinases such as chitin elicitor receptor kinase (HvCERK1) and protein kinases such as MAP kinase 3 (HvMPK3) and MAPK substrate 1 (HvMKS1), and transcription factors such as HvERF1/5, HvNAC42, HvWRKY23 and HvWRKY70 were also found upregulated with high fold change. Polymorphism studies across three barley genotypes confirmed the presence of mutations in HvCERK1 gene in two susceptible genotypes, isolating this gene as a potential candidate for FHB resistance. Further, the silencing of functional HvCERK1 gene in the resistant genotype CI9831, followed by gene expression and metabolite analysis revealed its role as an elicitor recognition receptor that triggered downstream regulatory genes, which in turn, regulated downstream metabolic pathway genes to biosynthesize resistance related (RR) metabolites to contain the pathogen to spikelet infection. A putative model on metabolic pathway regulation is proposed.

Chitin elicitor receptor kinase 1 (CERK1) is required for the non-host defense response of Arabidopsis to Fusarium oxysporum f. Sp. cubense

Banana wilt disease is a typical vascular disease caused by the fungal pathogen Fusarium oxysporum f. sp. cubense 4 (Foc 4). Pattern recognition receptors in the plant cell membrane can recognize pathogen-associated molecular patterns (PAMPs) to activate multi-layer defense responses, including defense gene expression, stomatal closure, reactive oxygen species (ROS) burst and callose deposition, to limit pathogen growth. In the present study, we found that chitin elicitor receptor kinase 1 (CERK1) was required for the non-host resistance of Arabidopsis thaliana to Foc B2 (a strain of Foc 4). The cerk1 mutant had weaker defense responses after Foc B2 treatment, including lower expression of PAMP- and salicylic acid-responsive genes, no stomatal closure, lower ROS level and less callose deposition, than that of the wild-type plant. Consistent with this, the cerk1 mutant plants exhibited higher susceptibility to non-host pathogen Foc B2. These results suggest the crucial importance of CERK1 in Foc B2-triggered non-host resistance.