L-type Lectin Receptor Kinases Research Articles

A group of L-type lectin receptor kinases function redundantly in mediating extracellular NAD(P) signaling in Arabidopsis.

An Arabidopsis mutant lacking several L-type lectin receptor kinases shows severely reduced NAD(P)-induced local and systemic immunity and biological induction of systemic acquired resistance.

Fortify the defense frontline: MAPKs phosphorylate receptor-like cytoplasmic kinase to maintain plant resistance in soybean

Mitogen-activated protein kinase (MAPK) activation is one of the significant immune events that respond to pathogens in plants. A MAPK cascade often contains a MAPK kinase kinase (MAPKKK), a MAPK kinase (MAPKK/MKK), and a MAPK. The well-characterized MAPK cascade, to date, is the MAPKKK3/4/5-MKK4/5-MPK3/6 module. Soybean cyst nematodes (SCN) is one of the most devastating soybean pathogens. However, the early immune components contributing to soybean resistance to SCN and the role of the MAPK cascade in the soybean–SCN interaction remain unclear. A recent study published in Plant Cell discovered that GmMPK3/6 phosphorylates a receptor-like cytoplasmic kinase (RLCK), CDG1-LIKE1 (GmCDL1), and maintains the stability of GmCDL1 in soybean. Remarkably, GmCDL1 enhances GmMPK3/6 activation and resistance to SCN by phosphorylating GmMAPKKK5 and activating the GmMAPKKK5-GmMKK4-GmMPK3/6 cascade. In addition, two L-type lectin receptor kinases (LecRKs), GmLecRK02g and GmLecRK08g, are involved in the GmCDL1 function after the perception of SCN. taken together, this study not only discovers a complete early immune pathway that responds to SCN infection in soybean, but also reveals a molecular mechanism by which plants maintain the activation of the MAPK cascade and resistance.

Mitogen-activated protein kinases MPK3 and MPK6 phosphorylate receptor-like cytoplasmic kinase CDL1 to regulate soybean basal immunity.

Soybean cyst nematode (SCN; Heterodera glycines Ichinohe), one of the most devastating soybean (Glycine max) pathogens, causes significant yield loss in soybean production. Nematode infection triggers plant defense responses; however, the components involved in the upstream signaling cascade remain largely unknown. In this study, we established that a mitogen-activated protein kinase (MAPK) signaling module, activated by nematode infection or wounding, is crucial for soybeans to establish SCN resistance. GmMPK3 and GmMPK6 directly interact with CDG1-LIKE1 (GmCDL1), a member of the receptor-like cytoplasmic kinase (RLCK) subfamily VII. These kinases phosphorylate GmCDL1 at Thr-372 to prevent its proteasome-mediated degradation. Functional analysis demonstrated that GmCDL1 positively regulates immune responses and promotes SCN resistance in soybeans. GmMPK3-mediated and GmMPK6-mediated phosphorylation of GmCDL1 enhances GmMPK3 and GmMPK6 activation and soybean disease resistance, representing a positive feedback mechanism. Additionally, 2 L-type lectin receptor kinases, GmLecRK02g and GmLecRK08g, associate with GmCDL1 to initiate downstream immune signaling. Notably, our study also unveils the potential involvement of GmLecRKs and GmCDL1 in countering other soybean pathogens beyond nematodes. Taken together, our findings reveal the pivotal role of the GmLecRKs-GmCDL1-MAPK regulatory module in triggering soybean basal immune responses.

Quantitative trait loci for sex ratio in monoecious bitter gourd (Momordica charantia)

Sex ratio (male or female flower frequency per plant) is an important trait of monoecious bitter gourds because it directly influences fruit yield. Quantitative trait loci (QTL) for the sex ratio were explored in F2 populations derived from the gynoecious OHB61-5 and monoecious OHB95-1A using both QTL mapping and QTL-seq methods. Female flower frequency data was used as the phenotype data, along with 1,036 bin-marker genotypes, and linkage maps from previous studies to detect sex ratio QTL. For QTL-seq, after the strong effect of the gynoecious locus was masked by marker-assisted selection of its heterozygotes, F2 plants showing higher- or lower-female flower frequency were selected and employed for making bulked samples. Three QTL were found on chromosomes 2 and 5 by QTL-seq, and only the qFR5-2 on chromosome 5 was identified by both QTL mapping and QTL-seq analyses. Focusing on the expressed genes with non-synonymous variations between parental lines in qFR5-2, 16 genes were nominated as candidate causal genes. Four of these encoded L-type lectin receptor kinase (LecRK), and amino acid substitutions in the conserved lectin or kinase domain were observed in three LecRKs between parental lines. Markers or genes for these sex ratio QTL will contribute to the development of bitter gourd inbred lines useful for stable production of fruits.

Transcriptome of weeping pinyon pine, Pinus pinceana, shows differences across heterogeneous habitats

We reconstructed the needle tissue Transcriptome of P. pinceana for individuals from distinct biogeographic regions across a temperature and precipitation gradient that represents its natural distribution. Gene expression analysis via RNA-Seq identified differential response to biotic stress. Phenotypic plasticity includes physiological traits affected by subtle changes in mRNA expression levels, causing different molecular phenotypes. We assessed the differential response to climate heterogeneity across the geographic range of Pinus pinceana G. Gordon & Glendinning. This pinyon pine shows a fragmented geographic distribution suggesting adaptation to the arid and extreme conditions of the eastern mountain slopes of the Chihuahuan desert. The geographic distribution of P. pinceana spans regions with significant variation in annual temperature and precipitation. We tested whether phenotypic divergence is supported by differences in expression profiles in P. pinceana mature trees along its natural distribution and corresponds to the changes in drought and other environmental stress. The reconstructed Transcriptome included 45,431 high-quality annotations derived from the needles of seven individuals across contrasting biogeographic and climatic localities. Trees from the driest regions shared active responses related to abiotic factors. The differential expression analysis identified intermediates and regulators of abiotic stress response for 26 genes, highlighting families involved in the environmental response to abiotic stress, and proteins linked to up-regulated responses, such as LRR receptor-like serine/threonine-protein kinase and L-type lectin receptor kinases (LecRK), directly related to pathogens. When Chihuahuan desert samples were compared with arboretum samples, we found differential expression of a regulator of root morphogenesis, cysteine-rich receptor-like protein kinase (CRK28), which could relate to differential absorption in drought conditions.

CaLecRK-S.5, a pepper L-type lectin receptor kinase gene, accelerates Phytophthora elicitin-mediated defense response

Innate immunity in plants relies on the recognition of pathogen-associated molecular patterns (PAMPs) by pattern-recognition receptors (PRRs) located on the plant cell surface. CaLecRK-S.5, a pepper L-type lectin receptor kinase, has been shown to confer broad-spectrum resistance through priming activation. To further elucidate the molecular mechanism of CaLecRK-S.5, transgenic tobacco plants were generated in this study. Interestingly, hemizygous transgenic plants exhibited a high accumulation of CaLecRK-S.5, but this accumulation was completely abolished in homozygous transgenic plants by a cosuppression mechanism. Gain-of-function and loss-of-function analyses revealed that CaLecRK-S.5 plays a positive role in Phytophthora elicitin-mediated defense responses.

The Arabidopsis Lectin Receptor Kinase LecRK-I.8 Is Involved in Insect Egg Perception.

Plants induce defense responses after insect egg deposition, but very little is known about the perception mechanisms. In Arabidopsis thaliana, eggs of the specialist insect Pieris brassicae trigger accumulation of reactive oxygen species (ROS) and salicylic acid (SA), followed by induction of defense genes and localized necrosis. Here, the involvement of the clade I L-type lectin receptor kinase LecRK-I.8 in these responses was studied. Expression of LecRK-I.8 was upregulated at the site of P. brassicae oviposition and egg extract (EE) treatment. ROS, SA, cell death, and expression of PR1 were substantially reduced in the Arabidopsis knock-out mutant lecrk-I.8 after EE treatment. In addition, EE-induced systemic resistance against Pseudomonas syringae was abolished in lecrk-I.8. Expression of ten clade I homologs of LecRK-I.8 was also induced by EE treatment, but single mutants displayed only weak alteration of EE-induced PR1 expression. These results demonstrate that LecRK-I.8 is an early component of egg perception.

L-type lectin receptor kinases: New forces in plant immunity.

L-type lectin receptor kinases: New forces in plant immunity.

LecRK-V, an L-type lectin receptor kinase in Haynaldia villosa, plays positive role in resistance to wheat powdery mildew.

SummaryPlant sense potential microbial pathogen using pattern recognition receptors (PRRs) to recognize pathogen‐associated molecular patterns (PAMPs). The Lectin receptor‐like kinase genes (LecRKs) are involved in various cellular processes mediated by signal transduction pathways. In the present study, an L‐type lectin receptor kinase gene LecRK‐V was cloned from Haynaldia villosa, a diploid wheat relative which is highly resistant to powdery mildew. The expression of LecRK‐V was rapidly up‐regulated by Bgt inoculation and chitin treatment. Its transcript level was higher in the leaves than in roots, culms, spikes and callus. Single‐cell transient overexpression of LecRK‐V led to decreased haustorium index in wheat variety Yangmai158, which is powdery mildew susceptible. Stable transformation LecRK‐V into Yangmai158 significantly enhanced the powdery mildew resistance at both seedling and adult stages. At seedling stage, the transgenic line was highly resistance to 18 of the tested 23 Bgt isolates, hypersensitive responses (HR) were observed for 22 Bgt isolates, and more ROS at the Bgt infection sites was accumulated. These indicated that LecRK‐V confers broad‐spectrum resistance to powdery mildew, and ROS and SA pathways contribute to the enhanced powdery mildew resistance in wheat.

CaLecRK-S.5, a pepper L-type lectin receptor kinase gene, confers broad-spectrum resistance by activating priming.

In Arabidopsis, several L-type lectin receptor kinases (LecRKs) have been identified as putative immune receptors. However, to date, there have been few analyses of LecRKs in crop plants. Virus-induced gene silencing of CaLecRK-S.5 verified the role of CaLecRK-S.5 in broad-spectrum resistance. Compared with control plants, CaLecRK-S.5-silenced plants showed reduced hypersensitive response, reactive oxygen species burst, secondary metabolite production, mitogen-activated protein kinase activation, and defense-related gene expression in response to Tobacco mosaic virus pathotype P0 (TMV-P0) infection. Suppression of CaLecRK-S.5 expression significantly enhanced the susceptibility to Pepper mild mottle virus pathotype P1,2,3, Xanthomonas campestris pv. vesicatoria, Phytophthora capsici, as well as TMV-P0 Additionally, β-aminobutyric acid treatment and a systemic acquired resistance assay revealed that CaLecRK-S.5 is involved in priming of plant immunity. Pre-treatment with β-aminobutyric acid before viral infection restored the reduced disease resistance phenotypes shown in CaLecRK-S.5-silenced plants. Systemic acquired resistance was also abolished in CaLecRK-S.5-silenced plants. Finally, RNA sequencing analysis indicated that CaLecRK-S.5 positively regulates plant immunity at the transcriptional level. Altogether, these results suggest that CaLecRK-S.5-mediated broad-spectrum resistance is associated with the regulation of priming.

Computational Analysis of the Ligand Binding Site of the Extracellular ATP Receptor, DORN1.

DORN1 (also known as P2K1) is a plant receptor for extracellular ATP, which belongs to a large gene family of legume-type (L-type) lectin receptor kinases. Extracellular ATP binds to DORN1 with strong affinity through its lectin domain, and the binding triggers a variety of intracellular activities in response to biotic and abiotic stresses. However, information on the tertiary structure of the ligand binding site of DORN1is lacking, which hampers efforts to fully elucidate the mechanism of receptor action. Available data of the crystal structures from more than 50 L-type lectins enable us to perform an in silico study of molecular interaction between DORN1 and ATP. In this study, we employed a computational approach to develop a tertiary structure model of the DORN1 lectin domain. A blind docking analysis demonstrated that ATP binds to a cavity made by four loops (defined as loops A B, C and D) of the DORN1 lectin domain with high affinity. In silico target docking of ATP to the DORN1 binding site predicted interaction with 12 residues, located on the four loops, via hydrogen bonds and hydrophobic interactions. The ATP binding pocket is structurally similar in location to the carbohydrate binding pocket of the canonical L-type lectins. However, four of the residues predicted to interact with ATP are not conserved between DORN1 and the other carbohydrate-binding lectins, suggesting that diversifying selection acting on these key residues may have led to the ATP binding activity of DORN1. The in silico model was validated by in vitro ATP binding assays using the purified extracellular lectin domain of wild-type DORN1, as well as mutated DORN1 lacking key ATP binding residues.

Ectopic expression of Arabidopsis L-type lectin receptor kinase genes LecRK-I.9 and LecRK-IX.1 in Nicotiana benthamiana confers Phytophthora resistance.

Key messageTransgenicNicotiana benthamianalines with constitutive expression of an Arabidopsis lectin receptor kinase gene (LecRK-I.9orLecRK-IX.1) show enhanced resistance toPhytophthorapathogens, demonstrating conserved gene functionality after interfamily transfer.In plants, cell surface receptors mediate the first layer of innate immunity against pathogenic microbes. In Arabidopsis several L-type lectin receptor kinases (LecRKs) were previously found to function as Phytophthora resistance components. In this study, we determined the functionality of Arabidopsis LecRK-I.9 or LecRK-IX.1 in Phytophthora resistance when transferred into the Solanaceous plant Nicotiana benthamiana. Multiple transgenic lines were generated for each LecRK gene and molecular analyses revealed variation in transgene copy number, transgene expression levels and LecRK protein accumulation. Infection assays showed that transgenic N. benthamiana plants expressing either Arabidopsis LecRK-I.9 or LecRK-IX.1 are more resistant to Phytophthora capsici and to Phytophthora infestans. These results demonstrate that Arabidopsis LecRK-I.9 and LecRK-IX.1 retained their Phytophthora resistance function when transferred into N. benthamiana. Therefore, these LecRKs have the potential to function as a complementary Phytophthora resistance resource in distantly related plant species next to the canonical Phytophthora resistance genes encoding nucleotide-binding leucine-rich repeat proteins.

Arabidopsis Lectin Receptor Kinases LecRK-IX.1 and LecRK-IX.2 Are Functional Analogs in Regulating Phytophthora Resistance and Plant Cell Death.

L-type lectin receptor kinases (LecRK) are potential immune receptors. Here, we characterized two closely-related Arabidopsis LecRK, LecRK-IX.1 and LecRK-IX.2, of which T-DNA insertion mutants showed compromised resistance to Phytophthora brassicae and Phytophthora capsici, with double mutants showing additive susceptibility. Overexpression of LecRK-IX.1 or LecRK-IX.2 in Arabidopsis and transient expression in Nicotiana benthamiana increased Phytophthora resistance but also induced cell death. Phytophthora resistance required both the lectin domain and kinase activity, but for cell death, the lectin domain was not needed. Silencing of the two closely related mitogen-activated protein kinase genes NbSIPK and NbNTF4 in N. benthamiana completely abolished LecRK-IX.1-induced cell death but not Phytophthora resistance. Liquid chromatography-mass spectrometry analysis of protein complexes coimmunoprecipitated in planta with LecRK-IX.1 or LecRK-IX.2 as bait, resulted in the identification of the N. benthamiana ABC transporter NbPDR1 as a potential interactor of both LecRK. The closest homolog of NbPDR1 in Arabidopsis is ABCG40, and coimmunoprecipitation experiments showed that ABCG40 associates with LecRK-IX.1 and LecRK-IX.2 in planta. Similar to the LecRK mutants, ABCG40 mutants showed compromised Phytophthora resistance. This study shows that LecRK-IX.1 and LecRK-IX.2 are Phytophthora resistance components that function independent of each other and independent of the cell-death phenotype. They both interact with the same ABC transporter, suggesting that they exploit similar signal transduction pathways.

L-type lectin receptor kinases in Nicotiana benthamiana and tomato and their role in Phytophthora resistance.

Membrane-bound receptors play crucial roles as sentinels of plant immunity against a large variety of invading microbes. One class of receptors known to be involved in self/non-self-surveillance and plant resistance comprises the L-type lectin receptor kinases (LecRKs). Previously, we reported that several Arabidopsis LecRKs play a role in resistance to Phytophthora pathogens. In this study, we determined whether homologues of these LecRKs from the Solanaceous plants Nicotiana benthamiana and tomato (Solanum lycopersicum) play similar roles in defence against Phytophthora. In genome-wide screenings, a total of 38 (Nb)LecRKs were identified in N. benthamiana and 22 (Sl)LecRKs in tomato, each consisting of both a lectin and a kinase domain. Phylogenetic analysis revealed that, in contrast to Arabidopsis, which has a LecRK family comprising nine clades, Solanaceous species have just five of these nine clades (i.e. IV, VI, VII, VIII, and IX), plus four additional clades that lack Arabidopsis homologues. Several of the Solanaceous LecRKs were selected for functional analysis using virus-induced gene silencing. Infection assays with Phytophthora capsici and Phytophthora infestans on LecRK-silenced plants revealed that N. benthamiana and tomato homologues in clade IX play a role in Phytophthora resistance similar to the two Arabidopsis LecRKs in this clade, suggesting conserved functions of clade IX LecRKs across different plant families. This study provides a first insight into the diversity of Solanaceous LecRKs and their role in plant immunity, and shows the potential of LecRKs for Phytophthora resistance breeding.

A complex interplay of tandem- and whole-genome duplication drives expansion of the L-type lectin receptor kinase gene family in the brassicaceae.

The comparative analysis of plant gene families in a phylogenetic framework has greatly accelerated due to advances in next generation sequencing. In this study, we provide an evolutionary analysis of the L-type lectin receptor kinase and L-type lectin domain proteins (L-type LecRKs and LLPs) that are considered as components in plant immunity, in the plant family Brassicaceae and related outgroups. We combine several lines of evidence provided by sequence homology, HMM-driven protein domain annotation, phylogenetic analysis, and gene synteny for large-scale identification of L-type LecRK and LLP genes within nine core-eudicot genomes. We show that both polyploidy and local duplication events (tandem duplication and gene transposition duplication) have played a major role in L-type LecRK and LLP gene family expansion in the Brassicaceae. We also find significant differences in rates of molecular evolution based on the mode of duplication. Additionally, we show that LLPs share a common evolutionary origin with L-type LecRKs and provide a consistent gene family nomenclature. Finally, we demonstrate that the largest and most diverse L-type LecRK clades are lineage-specific. Our evolutionary analyses of these plant immune components provide a framework to support future plant resistance breeding.

Phenotypic analyses of Arabidopsis T-DNA insertion lines and expression profiling reveal that multiple L-type lectin receptor kinases are involved in plant immunity.

L-type lectin receptor kinases (LecRK) are membrane-spanning receptor-like kinases with putative roles in biotic and abiotic stress responses and in plant development. In Arabidopsis, 45 LecRK were identified but their functions are largely unknown. Here, a systematic functional analysis was carried out by evaluating phenotypic changes of Arabidopsis LecRK T-DNA insertion lines in plant development and upon exposure to various external stimuli. None of the LecRK T-DNA insertion lines showed clear developmental changes, either under normal conditions or upon abiotic stress treatment. However, many of the T-DNA insertion lines showed altered resistance to Phytophthora brassicae, Phytophthora capsici, Pseudomonas syringae, or Alternaria brassicicola. One mutant defective in LecRK-V.5 expression was compromised in resistance to two Phytophthora spp. but showed enhanced resistance to Pseudomonas syringae. LecRK-V.5 overexpression confirmed its dual role in resistance and susceptibility depending on the pathogen. Combined analysis of these phenotypic data and LecRK expression profiles retrieved from public datasets revealed that LecRK which are hardly induced upon infection or even suppressed are also involved in pathogen resistance. Computed coexpression analysis revealed that LecRK with similar function displayed diverse expression patterns. Because LecRK are widespread in plants, the results presented here provide invaluable information for exploring the potential of LecRK as novel sources of resistance in crops.

Cucumis sativus L-type lectin receptor kinase (CsLecRK) gene family response to Phytophthora melonis, Phytophthora capsici and water immersion in disease resistant and susceptible cucumber cultivars

L-type lectin receptor kinase (LecRK) proteins are an important family involved in diverse biological processes such as pollen development, senescence, wounding, salinity and especially in innate immunity in model plants such as Arabidopsis and tobacco. Till date, LecRK proteins or genes of cucumber have not been reported. In this study, a total of 25 LecRK genes were identified in the cucumber genome, unequally distributed across its seven chromosomes. According to similarity comparison of their encoded proteins, the Cucumis sativus LecRK (CsLecRK) genes were classified into six major clades (from Clade I to CladeVI). Expression of CsLecRK genes were tested using QRT-PCR method and the results showed that 25 CsLecRK genes exhibited different responses to abiotic (water immersion) and biotic (Phytophthora melonis and Phytophthora capsici inoculation) stresses, as well as that between disease resistant cultivar (JSH) and disease susceptible cultivar (B80). Among the 25 CsLecRK genes, we found CsLecRK6.1 was especially induced by P. melonis and P. capsici in JSH plants. All these results suggested that CsLecRK genes may play important roles in biotic and abiotic stresses.

The Arabidopsis lectin receptor kinase LecRK‐I.9 enhances resistance to Phytophthora infestans in Solanaceous plants

Late blight caused by the plant pathogenic oomycete Phytophthora infestans is known as one of the most destructive potato diseases. Plant breeders tend to employ NB-LRR-based resistance for introducing genetically controlled late blight resistance in their breeding lines. However, P.infestans is able to rapidly escape this type of resistance, and hence, NB-LRR-based resistance in potato cultivars is often not durable. Previously, we identified a novel type of Phytophthora resistance in Arabidopsis. This resistance is mediated by the cell surface receptor LecRK-I.9, which belongs to the family of L-type lectin receptor kinases. In this study, we report that expression of the Arabidopsis LecRK-I.9 gene in potato and Nicotiana benthamiana results in significantly enhanced late blight resistance. Transcriptional profiling showed strong reduction in salicylic acid (SA)-mediated defence gene expression in LecRK-I.9 transgenic potato lines (TPLs). In contrast, transcripts of two protease inhibitor genes accumulated to extreme high levels, suggesting that LecRK-I.9-mediated late blight resistance is relying on a defence response that includes activation of protease inhibitors. These results demonstrate that the functionality of LecRK-I.9 in Phytophthora resistance is maintained after interfamily transfer to potato and N.benthamiana and suggest that this novel type of LecRK-based resistance can be exploited in breeding strategies to improve durable late blight resistance in Solanaceous crops.