Leucine-rich Repeat Receptor-like Protein Research Articles

C-terminal frameshift mutations generate viable knockout mutants with developmental defects for three essential protein kinases

AbstractLoss-of-function mutants are fundamental resources for gene function studies. However, it is difficult to generate viable and heritable knockout mutants for essential genes. Here, we show that targeted editing of the C-terminal sequence of the embryo lethal gene MITOGEN-ACTIVATED PROTEIN KINASES 1 (OsMPK1) results in weak mutants. This C-terminal-edited osmpk1 mutants displayed severe developmental defects and altered disease resistance but generated tens of viable seeds that inherited the mutations. Using the same C-terminal editing approach, we also obtained viable mutants for a wall-associated protein kinase (Os07g0493200) and a leucine-rich repeat receptor-like protein kinase (Os01g0239700), while the null mutations of these genes were lethal. These data suggest that protein kinase activity could be reduced by introducing frameshift mutations adjacent to the C-terminus, which could generate valuable resources for gene function studies and tune protein kinase activity for signaling pathway engineering.

Identification of Quantitative Trait Loci Controlling Root Morphological Traits in an Interspecific Soybean Population Using 2D Imagery Data.

Roots are the hidden and most important part of plants. They serve as stabilizers and channels for uptaking water and nutrients and play a crucial role in the growth and development of plants. Here, two-dimensional image data were used to identify quantitative trait loci (QTL) controlling root traits in an interspecific mapping population derived from a cross between wild soybean 'PI366121' and cultivar 'Williams 82'. A total of 2830 single-nucleotide polymorphisms were used for genotyping, constructing genetic linkage maps, and analyzing QTLs. Forty-two QTLs were identified on twelve chromosomes, twelve of which were identified as major QTLs, with a phenotypic variation range of 36.12% to 39.11% and a logarithm of odds value range of 12.01 to 17.35. Two significant QTL regions for the average diameter, root volume, and link average diameter root traits were detected on chromosomes 3 and 13, and both wild and cultivated soybeans contributed positive alleles. Six candidate genes, Glyma.03G027500 (transketolase/glycoaldehyde transferase), Glyma.03G014500 (dehydrogenases), Glyma.13G341500 (leucine-rich repeat receptor-like protein kinase), Glyma.13G341400 (AGC kinase family protein), Glyma.13G331900 (60S ribosomal protein), and Glyma.13G333100 (aquaporin transporter) showed higher expression in root tissues based on publicly available transcriptome data. These results will help breeders improve soybean genetic components and enhance soybean root morphological traits using desirable alleles from wild soybeans.

Genome-Wide Identification and Expression Analysis of Kiwifruit Leucine-Rich Repeat Receptor-Like Proteins Reveal Their Roles in Biotic and Abiotic Stress Responses.

Leucine-rich repeat receptor-like proteins (LRR-RLPs), a major group of receptor-like proteins in plants, have diverse functions in plant physiology, including growth, development, signal transduction, and stress responses. Despite their importance, the specific roles of kiwifruit LRR-RLPs in response to biotic and abiotic stresses remain poorly understood. In this study, we performed family identification, characterization, transcriptome data analysis, and differential gene expression analysis of kiwifruit LRR-RLPs. We identified totals of 101, 164, and 105 LRR-RLPs in Actinidia chinensis 'Hongyang', Actinidia eriantha 'Huate', and Actinidia chinensis 'Red5', respectively. Synteny analysis revealed that the expansion of kiwifruit LRR-RLPs was primarily attributed to segmental duplication events. Based on RNA-seq data from pathogen-infected kiwifruits, we identified specific LRR-RLP genes potentially involved in different stages of pathogen infection. Additionally, we observed the potential involvement of kiwifruit LRR-RLPs in abiotic stress responses, with upstream transcription factors possibly regulating their expression. Furthermore, protein interaction network analysis unveiled the participation of kiwifruit LRR-RLP in the regulatory network of abiotic stress responses. These findings highlight the crucial roles of LRR-RLPs in mediating both biotic and abiotic stress responses in kiwifruit, offering valuable insights for the breeding of stress-resistant kiwifruit varieties.

Integrated Analysis of lncRNAs and mRNAs Reveals Complex Gene Network Mediated by lncRNAs and Regulatory Function of MuLRR-RLK-AS in Response to Phytoplasma Infection in Mulberry.

Phytoplasma disease is one of the most serious infectious diseases that affects the growth and development of mulberry. Long non-coding RNAs (lncRNAs) play an important role in plants' defense systems; however, the contribution of lncRNAs in the response to phytoplasma infection in mulberry is still largely unknown. Herein, strand-specific RNA sequencing was performed to profile the mRNAs and lncRNAs involved in the response to phytoplasma infection in mulberry, and a total of 4169 genes were found to be differentially expressed (DE) between healthy and phytoplasma-infected leaves. Moreover, 1794 lncRNAs were identified, of which 742 lncRNAs were DE between healthy and infected leaves. Target prediction showed that there were 68 and 44 DE lncRNAs which may function as cis and trans-regulators, targeting 54 and 44 DE genes, respectively. These DE target genes are associated with biological processes such as metabolism, signaling, development, transcriptional regulation, etc. In addition, it was found that the expression of the antisense lncRNA (MuLRR-RLK-AS) of the leucine-rich repeat receptor-like protein kinase gene (MuLRR-RLK) was decreased in the phytoplasma-infected leaves. Interestingly, it was found that overexpression of MuLRR-RLK-AS can inhibit the expression of MuLRR-RLK. Moreover, it was found that the expression levels of PTI-related and MAPK genes in the transgenic MuLRR-RLK Arabidopsis plants were significantly higher than those in the wild-type plants when inoculated with pathogens, and the transgenic plants were conferred with strong disease resistance. Our results demonstrate that MuLRR-RLK-AS, as a trans-regulatory factor, can inhibit the expression of the MuLRR-RLK gene and is a negative regulatory factor for mulberry resistance. The information provided is particularly useful for understanding the functions and mechanisms of lncRNAs in the response to phytoplasma infection in mulberry.

Histological, chemical and gene expression differences between western redcedar seedlings resistant and susceptible to cedar leaf blight.

Western redcedar (Thuja plicata) is an important species in the Cupressaceae both at economic and cultural levels in the Pacific Northwest of North America. In adult trees, the species produces one of the most weathering-resistant heartwoods among conifers, making it one of the preferred species for outdoor applications. However, young T. plicata plants are susceptible to infection with cedar leaf blight (Didymascella thujina), an important foliar pathogen that can be devastating in nurseries and small-spaced plantations. Despite that, variability in the resistance against D. thujina in T. plicata has been documented, and such variability can be used to breed T. plicata for resistance against the pathogen. This investigation aimed to discern the phenotypic and gene expression differences between resistant and susceptible T. plicata seedlings to shed light on the potential constitutive resistance mechanisms against cedar leaf blight in western redcedar. The study consisted of two parts. First, the histological differences between four resistant and four susceptible families that were never infected with the pathogen were investigated. And second, the differences between one resistant and one susceptible family that were infected and not infected with the pathogen were analyzed at the chemical (C, N, mineral nutrients, lignin, fiber, starch, and terpenes) and gene expression (RNA-Seq) levels. The histological part showed that T. plicata seedlings resistant to D. thujina had constitutively thicker cuticles and lower stomatal densities than susceptible plants. The chemical analyses revealed that, regardless of their infection status, resistant plants had higher foliar concentrations of sabinene and α-thujene, and higher levels of expression of transcripts that code for leucine-rich repeat receptor-like protein kinases and for bark storage proteins. The data collected in this study shows that constitutive differences at the phenotypic (histological and chemical) and gene expression level exist between T. plicata seedlings susceptible and resistant to D. thujina. Such differences have potential use for marker-assisted selection and breeding for resistance against cedar leaf blight in western redcedar in the future.

Evolutionary trajectory of pattern recognition receptors in plants

Cell-surface receptors play pivotal roles in many biological processes, including immunity, development, and reproduction, across diverse organisms. How cell-surface receptors evolve to become specialised in different biological processes remains elusive. To shed light on the immune-specificity of cell-surface receptors, we analyzed more than 200,000 genes encoding cell-surface receptors from 350 genomes and traced the evolutionary origin of immune-specific leucine-rich repeat receptor-like proteins (LRR-RLPs) in plants. Surprisingly, we discovered that the motifs crucial for co-receptor interaction in LRR-RLPs are closely related to those of the LRR-receptor-like kinase (RLK) subgroup Xb, which perceives phytohormones and primarily governs growth and development. Functional characterisation further reveals that LRR-RLPs initiate immune responses through their juxtamembrane and transmembrane regions, while LRR-RLK-Xb members regulate development through their cytosolic kinase domains. Our data suggest that the cell-surface receptors involved in immunity and development share a common origin. After diversification, their ectodomains, juxtamembrane, transmembrane, and cytosolic regions have either diversified or stabilised to recognise diverse ligands and activate differential downstream responses. Our work reveals a mechanism by which plants evolve to perceive diverse signals to activate the appropriate responses in a rapidly changing environment.

Phytosulfokine receptor 1 (AtPSKR1) acts as a positive regulator of leaf senescence by mediating ROS signaling in Arabidopsis thaliana

Leaf senescence represents an active and regulated degeneration process. Leucine-rich repeat receptor-like protein kinase (LRR-RLK) represents a large group of cell surface receptors that play important roles in multiple biological processes, and some are also known to regulate the senescence process. In the present study, we elucidated the involvement of Phytosulfokine Receptor (PSKR) gene in the regulation of leaf senescence. The expression of PSKR1 of Arabidopsis was found to be up-regulated during leaf senescence. The over-expressing lines of AtPSKR1 and its rice homologue OsPSKR10 displayed an early leaf senescent phenotype in Arabidopsis, while the late senescence in mutant line of AtPSKR1 supported the idea that PSKR positively regulate the process of leaf senescence. Furthermore, the leaves of the overexpressing lines displayed increased superoxide accumulation compared to mutant lines, along with higher expression of NADPH oxidases (AtRBOHD and AtRBOHF). Importantly, our findings demonstrates that both AtPSKR1and OsPSKR10 interact with AtRBOHD and AtRBOHF and thereby instigating superoxide accumulation in the leaves through NADPH oxidases.

The CAP superfamily protein PsCAP1 secreted by Phytophthora triggers immune responses in Nicotiana benthamiana through a leucine-rich repeat receptor-like protein.

The role of cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 (CAP) superfamily proteins in the innate immune responses of mammals is well characterized. However, the biological function of CAP superfamily proteins in plant-microbe interactions is poorly understood. We used proteomics and transcriptome analyses to dissect the apoplastic effectors secreted by the oomycete Phytophthora sojae during early infection of soybean leaves. By transiently expressing these effectors in Nicotiana benthamiana, we identified PsCAP1, a novel type of secreted CAP protein that triggers immune responses in multiple solanaceous plants including N. benthamiana. This secreted CAP protein is conserved among oomycetes, and multiple PsCAP1 homologs can be recognized by N. benthamiana. PsCAP1-triggered immune responses depend on the N-terminal immunogenic fragment (aa 27-151). Pretreatment of N. benthamiana with PsCAP1 or the immunogenic fragment increases plant resistance against Phytophthora. The recognition of PsCAP1 and different homologs requires the leucine-rich repeat receptor-like protein RCAP1, which associates with two central receptor-like kinases BRI1-associated receptor kinase 1 (BAK1) and suppressor of BIR1-1 (SOBIR1) in planta. These findings suggest that the CAP-type apoplastic effectors act as an important player in plant-microbe interactions that can be perceived by plant membrane-localized receptor to activate plant resistance.

ORYZA SATIVA SPOTTED-LEAF 41 (OsSPL41) Negatively Regulates Plant Immunity in Rice

Identification of immunity-associated leucine-rich repeat receptor-like protein kinases (LRR-RLK) is critical to elucidate the LRR-RLK mediated mechanism of plant immunity. Here, we reported the map-based cloning of a novel rice SPOTTED-LEAF 41 (OsSPL41) encoding a putative LRR-RLK protein (OsLRR-RLK41/OsSPL41) that regulated disease responses to the bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). An 8-bp insertion at position 865 bp in a mutant spotted-leaf 41 (spl41) allele led to the formation of purple-brown lesions on leaves. Functional complementation by the wild type allele (OsSPL41) can rescue the mutant phenotype, and the complementary lines showed similar performance to wild type in a number of agronomic, physiological and molecular indices. OsSPL41 was constitutively expressed in all tissues tested, and OsSPL41 contains a typical transmembrane domain critical for its localization to the cell membrane. The mutant exhibited an enhanced level of resistance to Xoo in companion of markedly up-regulated expression of pathogenesis-related genes such as OsPR10a, OsPAL1 and OsNPR1, while the level of salicylic acid was significantly increased in spl41. In contrast, the over-expression lines exhibited a reduced level of H2O2 and were much susceptible to Xoo with down-regulated expression of pathogenesis-related genes. These results suggested that OsSPL41 might negatively regulate plant immunity through the salicylic acid signaling pathway in rice.

A Phytophthora receptor-like kinase regulates oospore development and can activate pattern-triggered plant immunity

Plant cell-surface leucine-rich repeat receptor-like kinases (LRR-RLKs) and receptor-like proteins (LRR-RLPs) form dynamic complexes to receive a variety of extracellular signals. LRR-RLKs are also widespread in oomycete pathogens, whereas it remains enigmatic whether plant and oomycete LRR-RLKs could mediate cell-to-cell communications between pathogen and host. Here, we report that an LRR-RLK from the soybean root and stem rot pathogen Phytophthora sojae, PsRLK6, can activate typical pattern-triggered immunity in host soybean and nonhost tomato and Nicotiana benthamiana plants. PsRLK6 homologs are conserved in oomycetes and also exhibit immunity-inducing activity. A small region (LRR5-6) in the extracellular domain of PsRLK6 is sufficient to activate BAK1- and SOBIR1-dependent immune responses, suggesting that PsRLK6 is likely recognized by a plant LRR-RLP. Moreover, PsRLK6 is shown to be up-regulated during oospore maturation and essential for the oospore development of P. sojae. Our data provide a novel type of microbe-associated molecular pattern that functions in the sexual reproduction of oomycete, and a scenario in which a pathogen LRR-RLK could be sensed by a plant LRR-RLP to mount plant immunity.

The Leucine-Rich Repeat Receptor-Like Kinase Protein TaSERK1 Positively Regulates High-Temperature Seedling Plant Resistance to Puccinia striiformis f. sp. tritici by Interacting with TaDJA7.

Somatic embryogenesis receptor kinases (SERKs) belong to the leucine-rich repeat receptor-like kinase (LRR-RLK) subfamily, and many LRR-RLKs have been proven to play a key role in plant immune signal transmission. However, the functions of SERKs in resistance to stripe rust caused by Puccinia striiformis f. sp. tritici remains unknown. Here, we identified a gene, TaSERK1, from Xiaoyan 6, a wheat cultivar possessing high-temperature seedling-plant (HTSP) resistance to the fungal pathogen P. striiformis f. sp. tritici and expresses its resistance at the seedling stage. The expression level of TaSERK1 was upregulated upon P. striiformis f. sp. tritici inoculation under relatively high temperatures. The transcriptional level of TaSERK1 was significantly increased under exogenous salicylic acid and brassinosteroids treatments. The barley stripe mosaic virus-induced gene silencing assay indicated that TaSERK1 positively regulated the HTSP resistance to stripe rust. The transient expression of TaSERK1 in tobacco leaves confirmed its subcellular localization on the plasma membrane. Furthermore, TaSERK1 interacted with and phosphorylated the chaperone protein TaDJA7, which belongs to the heat shock protein 40 subfamily. Silencing TaDJA7 compromised the HTSP resistance to stripe rust. The results indicated that when the membrane immune receptor TaSERK1 perceives the P. striiformis f. sp. tritici infection under relatively high temperatures, it transmits the signal to TaDJA7 to activate HTSP resistance to the pathogen.

Four haplotype blocks linked to Ascochyta blight disease resistance in chickpea under Mediterranean conditions

Ascochyta blight, caused by the fungal pathogen Ascochyta blight, caused by the fungal pathogen Ascochyta rabiei, is a devastating biotic stress that poses a significant threat to chickpea cultivation worldwide. To combat this disease, breeding programs have focused on developing cultivars with resistance to Ascochyta blight. However, a comprehensive understanding of the underlying plant defense mechanism is still lacking. To identify genomic regions associated with resistance, a recombinant inbred line (RIL) population was created by crossing ILC3279 (kabuli, resistant) and WR315 (desi, susceptible), which was then phenotyped and sequenced using a tuneable genotyping-by-sequencing (tGBS) protocol to obtain single nucleotide polymorphisms (SNPs). We further validated the association of genomic regions with Ascochyta blight resistance in a second recombinant inbred line\population derived from the cross between JG62 (desi, susceptible) and ILC72 (kabuli, resistant). Our analysis identified four genomic regions associated with Ascochyta blight resistance in chromosomes 2 and 4, among which a region spanning from 3.52 to 8.20 Mb in chromosome 4 was the most robust candidate for resistance, being associated with resistance in both years and populations. A total of 30 genes from the identified regions were selected as robust candidates, and LOC101507066, which encodes a leucine-rich repeat receptor-like protein kinase, was the most robust candidate gene, as it plays critical roles in plant stress responses and immunity. Our findings have potential to accelerate marker-assisted genetic improvement and facilitate the development of integrated strategies for crop protection.

Genome-wide association mapping for LLS resistance in a MAGIC population of groundnut (Arachis hypogaea L.).

The identified30 functional nucleotide polymorphisms or genic SNP markers would offer essential information for marker-assisted breeding in groundnut. A genome-wide association study (GWAS) on component traits of LLS resistance in an eight-way multiparent advance generation intercross (MAGIC) population of groundnut in the field and in a light chamber (controlled conditions) was performed via an Affymetrix 48K single-nucleotide polymorphism (SNP) 'Axiom Arachis' array. Multiparental populations with high-density genotyping enable the detection of novel alleles. In total, five quantitative trait loci (QTLs) with marker - log10(p value) scores ranging from 4.25 to 13.77 for the incubation period (IP) and six QTLs with marker - log10(p value) scores ranging from 4.33 to 10.79 for the latent period (LP) were identified across the A- and B-subgenomes. A total of 62 markers‒trait associations (MTAs) were identified across the A- and B-subgenomes. Markers for LLS scores and the area under the disease progression curve (AUDPC) recorded for plants in the light chamber and under field conditions presented - log10 (p value) scores ranging from 4.22 to 27.30. The highest number of MTAs (six) was identified on chromosomes A05, B07 and B09. Out of a total of 73 MTAs, 37 and 36 MTAs were detected in subgenomes A and B, respectively. Taken together, these results suggest that both subgenomes have equal potential genomic regions contributing to LLS resistance. A total of 30 functional nucleotide polymorphisms or genic SNP markers were detected, among which eight genes were found to encode leucine-rich repeat (LRR) receptor-like protein kinases and putative disease resistance proteins. These important SNPs can be used in breeding programmes for the development of cultivars with improved disease resistance.

Genome-wide association study reveals novel loci and acandidate gene for resistance to frogeye leaf spot (Cercospora sojina) in soybean.

Frogeye leaf spot, caused by the fungus Cercospora sojina, is a threat to soybeans in the southeastern and midwestern United States that can be controlled by crop genetic resistance. Limited genetic resistance to the disease has been reported, and only three sources of resistance have been used in modern soybean breeding. To discover novel sources and identify the genomic locations of resistance that could be used in soybean breeding, a GWAS was conducted using a panel of 329 soybean accessions selected to maximize genetic diversity. Accessions were phenotyped using a 1-5 visual rating and by using image analysis to count lesion number and measure the percent of leaf area diseased. Eight novel loci on eight chromosomes were identified for three traits utilizing the FarmCPU or BLINK models, of which a locus on chromosome 11 was highly significant across all model-trait combinations. KASP markers were designed using the SoySNP50K Beadchip and variant information from 65 of the accessions that have been sequenced to target SNPs in the gene model Glyma.11g230400, a LEUCINE-RICH REPEAT RECEPTOR-LIKE PROTEIN KINASE. The association of a KASP marker, GSM990, designed to detect a missense mutation in the gene was the most significant with all three traits in a genome-wide association, and the marker may be useful to select for resistance to frogeye leaf spot in soybean breeding.

Identification of major quantitative trait loci and candidate genes for seed weight in soybean

Key messageFour major quantitative trait loci for 100-seed weight were identified in a soybean RIL population under five environments, and the most likely candidate genes underlying these loci were identified.Seed weight is an important target of soybean breeding. However, the genes underlying the major quantitative trait loci (QTL) controlling seed weight remain largely unknown. In this study, a soybean population of 300 recombinant inbred lines (RILs) derived from a cross between PI595843 (PI) and WH was used to map the QTL and identify candidate genes for seed weight. The RIL population was genotyped through whole genome resequencing, and phenotyped for 100-seed weight under five environments. A total of 38 QTL were detected, and four major QTL, each explained at least 10% of the variation in 100-seed weight, were identified. Six candidate genes within these four major QTL regions were identified by analyses of their tissue expression patterns, gene annotations, and differential gene expression levels in soybean seeds during four developmental stages between two parental lines. Further sequence variation analyses revealed a C to T substitution in the first exon of the Glyma.19G143300, resulting in an amino acid change between PI and WH, and thus leading to a different predicted kinase domain, which might affect its protein function. Glyma.19G143300 is highly expressed in soybean seeds and encodes a leucine-rich repeat receptor-like protein kinase (LRR-RLK). Its predicted protein has typical domains of LRR-RLK family, and phylogenetic analyses reveled its similarity with the known LRR-RLK protein XIAO (LOC_Os04g48760), which is involved in controlling seed size. The major QTL and candidate genes identified in this study provide useful information for molecular breeding of new soybean cultivars with desirable seed weight.

An Integration of Linkage Mapping and GWAS Reveals the Key Genes for Ear Shank Length in Maize

Ear shank length (ESL) has significant effects on grain yield and kernel dehydration rate in maize. Herein, linkage mapping and genome-wide association study were combined to reveal the genetic architecture of maize ESL. Sixteen quantitative trait loci (QTL) were identified in the segregation population, among which five were repeatedly detected across multiple environments. Meanwhile, 23 single nucleotide polymorphisms were associated with the ESL in the association panel, of which four were located in the QTL identified by linkage mapping and were designated as the population-common loci. A total of 42 genes residing in the linkage disequilibrium regions of these common variants and 12 of them were responsive to ear shank elongation. Of the 12 genes, five encode leucine-rich repeat receptor-like protein kinases, proline-rich proteins, and cyclin11, respectively, which were previously shown to regulate cell division, expansion, and elongation. Gene-based association analyses revealed that the variant located in Cyclin11 promoter affected the ESL among different lines. Cyclin11 showed the highest expression in the ear shank 15 days after silking among diverse tissues of maize, suggesting its role in modulating ESL. Our study contributes to the understanding of the genetic mechanism underlying maize ESL and genetic modification of maize dehydration rate and kernel yield.

Leucine-Rich Repeat Receptor-Like Proteins in Plants: Structure, Function, and Signaling

Leucine-Rich Repeat Receptor-Like Proteins in Plants: Structure, Function, and Signaling

Dissection of leucine-rich repeat receptor-like protein kinases: insight into resistance to Fusarium wilt in tung tree.

The tung tree is a woody oil plant native to China and widely distributed in the subtropics. The three main species commonly known as Vernicia are V. fordii, V. montana, and V. cordata. The growth and development of V. fordii are affected by a large number of plant pathogens, such as Fusarium wilt caused by Fusarium sp. In contrast, V. montana shows significant resistance to Fusarium wilt. The leucine-rich repeat receptor-like protein kinase (LRR-RLK) is the largest class of receptor-like kinases associated with plant resistance to Fusarium wilt. Here, we identified 239 VmLRR-RLKs in V. montana, and found that there were characteristic domains of resistance to Fusarium wilt in them. Phylogenetic analysis suggested that the VmLRR-RLKs are divided into 14 subfamilies, indicating that homologous genes in the same group may have similar functions. Chromosomal localization analysis showed that VmLRR-RLKs were unevenly distributed on chromosomes, and segment duplications were the main reason for the expansion of VmLRR-RLK family members. The transcriptome data showed that six orthologous pairs were up-regulated in V. montana in response to Fusarium wilt, while the corresponding orthologous genes showed low or no expression in V. fordii in resistance Fusarium wilt, further indicating the important role of LRR-RLKs in V. montana's resistance to infection by Fusarium spp. Our study provides important reference genes for the future use of molecular breeding to improve oil yield and control of Fusarium wilt in tung tree.

Functional analysis of Rehmannia glutinosa key LRR-RLKs during interaction of root exudates with Fusarium oxysporum reveals the roles of immune proteins in formation of replant disease.

Previous studies have indicated that some Rehmannia glutinosa Leucine-rich repeat receptor-like protein kinases (LRR-RLKs) are involved in the formation of replant disease. However, it remains unclear how the interaction of LRR-RLKs with a key factor, the interaction between root exudates and Fusarium oxysporum, results in formation of replant disease. In this study, the influences of root exudates, F. oxysporum and the interaction of these two factors on expression of nine R. glutinosa LRR-RLKs (RgLRRs) were analyzed. The resulting eight RgLRRs of them were highly expressed at the early stage, and rapidly declined at later stages under mixed treatment of root exudates and F. oxysporum. The functions of nine RgLRRs under root exudates, F. oxysporum and mixed treatment of root exudates and F. oxysporum were preliminarily analyzed using transient overexpression and RNAi experiments. The results showed that high expression of RgLRR19, RgLRR21, RgLRR23 and RgLRR29 could decrease the damage to root cells from the mixed treatment of root exudates and F. oxysporum, but the interference of these genes enhanced the damage levels of root cells. Based on this, stable transgenic R. glutinosa seedlings were acquired. Overexpression of RgLRR29 conferred resistance of R. glutinosa seedlings to root exudates, F. oxysporum and mixed treatment. These results indicated that the continuous proliferation of F. oxysporum supported by root exudates altered the expression patterns of RgLRRs in R. glutinosa, then disordered the growth and development of R. glutinosa, finally leading to the formation of replant disease.

An F-box protein attenuates fungal xylanase-triggered immunity by destabilizing LRR-RLP NbEIX2 in a SOBIR1-dependent manner.

Receptor-like proteins (RLPs) lacking the cytoplasmic kinase domain play crucial roles in plant growth, development and immunity. However, what remains largely elusive is whether RLP protein levels are fine-tuned by E3 ubiquitin ligases, which are employed by receptor-like kinases for signaling attenuation. Nicotiana benthamiana NbEIX2 is a leucine-rich repeat RLP (LRR-RLP) that mediates fungal xylanase-triggered immunity. Here we show that NbEIX2 associates with an F-box protein NbPFB1, which promotes NbEIX2 degradation likely by forming an SCF E3 ubiquitin ligase complex, and negatively regulates NbEIX2-mediated immune responses. NbEIX2 undergoes ubiquitination and proteasomal degradation in planta. Interestingly, NbEIX2 without its cytoplasmic tail is still associated with and destabilized by NbPFB1. In addition, NbPFB1 also associates with and destabilizes NbSOBIR1, a co-receptor of LRR-RLPs, and fails to promote NbEIX2 degradation in the sobir1 mutant. Our findings reveal a distinct model of NbEIX2 degradation, in which an F-box protein destabilizes NbEIX2 indirectly in a SOBIR1-dependent manner.