Genome-Wide Survey Indicates Diverse Physiological Roles of Dendrobium officinale Calcium-Dependent Protein Kinase Genes.

Calcium-dependent protein kinases (CDPKs) are crucial calcium ions (Ca2+) sensors in plants with important roles in signal transduction, plant growth, development, and stress responses. Here, we identified 24 genes encoding CDPKs in Dendrobium officinale using genome-wide analysis. The phylogenetic analysis revealed that these genes formed four groups, with similar structures in the same group. The gene expression patterns following hormone treatments and yeast two-hybrid of homologous CDPK gene pairs with Rbohs showed differences, indicating functional divergence between homologous genes. In addition, the rapid accumulation of hydrogen peroxide (H2O2) and stomatal closure was observed in response to salicylic acid (SA)/jasmonic acid (JA) stress. Our data showed that CDPK9-2 and CDPK20-4 interacted with Rboh D and Rboh H, respectively, and were implicated in the generation of H2O2 and regulation of the stomatal aperture in response to salicylic acid/jasmonic acid treatment. We believe these results can provide a foundation for the functional divergence of homologous genes in D. officinale.

Loss of LKB1-NUAK1 signalling enhances NF-κB activity in a spheroid model of high-grade serous ovarian cancer.

High-grade serous ovarian cancer (HGSOC) is an aggressive malignancy often diagnosed at an advanced stage. Although most HGSOC patients respond initially to debulking surgery combined with cytotoxic chemotherapy, many ultimately relapse with platinum-resistant disease. Thus, improving outcomes requires new ways of limiting metastasis and eradicating residual disease. We identified previously that Liver kinase B1 (LKB1) and its substrate NUAK1 are implicated in EOC spheroid cell viability and are required for efficient metastasis in orthotopic mouse models. Here, we sought to identify additional signalling pathways altered in EOC cells due to LKB1 or NUAK1 loss-of-function. Transcriptome analysis revealed that inflammatory signalling mediated by NF-κB transcription factors is hyperactive due to LKB1-NUAK1 loss in HGSOC cells and spheroids. Upregulated NF-κB signalling due to NUAK1 loss suppresses reactive oxygen species (ROS) production and sustains cell survival in spheroids. NF-κB signalling is also activated in HGSOC precursor fallopian tube secretory epithelial cell spheroids, and is further enhanced by NUAK1 loss. Finally, immunohistochemical analysis of OVCAR8 xenograft tumors lacking NUAK1 displayed increased RelB expression and nuclear staining. Our results support the idea that NUAK1 and NF-κB signalling pathways together regulate ROS and inflammatory signalling, supporting cell survival during each step of HGSOC pathogenesis. We propose that their combined inhibition may be efficacious as a novel therapeutic strategy for advanced HGSOC.

Sensing plasma membrane pore formation induces chemokine production in survivors of regulated necrosis.

Although overwhelming plasma membrane integrity loss leads to cell lysis and necrosis, cells can tolerate a limited level of plasma membrane damage, undergo ESCRT-III-mediated repair, and survive. Here, we find that cells which undergo limited plasma membrane damage from the pore-forming actions of MLKL, GSDMD, perforin, or detergents experience local activation of PKCs through Ca2+ influx at the damage sites. S660-phosphorylated PKCs subsequently activate the TAK1/IKKs axis and RelA/Cux1 complex to trigger chemokine expressions. We observe that in late-stage cancers, cells with active MLKL show expression of CXCL8. Similar expression induction is also found in ischemia-injured kidneys. Chemokines generated in this manner are also indispensable for recruiting immune cells to the dead and dying cells. This plasma membrane integrity-sensing pathway is similar to the well-established yeast cell wall integrity signaling pathway at molecular level, and this suggests an evolutionary conserved mechanism to respond to the cellular barrier damage.

Cloning and functional analysis of the novel rice blast resistance gene Pi65 in japonica rice.

KEY MESSAGE: Pi65, a leucine-rich repeat receptor-like kinase (LRR-RLK) domain cloned from Oryza sativa japonica, is a novel rice blast disease resistance gene. Rice blast seriously threatens rice production worldwide. Utilizing the rice blast resistance gene to breed rice blast-resistant varieties is one of the best ways to control rice blast disease. Using a map-based cloning strategy, we cloned a novel rice blast resistance gene, Pi65, from the resistant variety GangYu129 (abbreviated GY129, Oryza sativa japonica). Overexpression of Pi65 in the susceptible variety LiaoXing1 (abbreviated LX1, Oryza sativa japonica) enhanced rice blast resistance, while knockout of Pi65 in GY129 resulted in susceptibility to rice blast disease. Pi65 encodes two transmembrane domains, with 15 LRR domains and one serine/threonine protein kinase catalytic domain, conferring resistance to isolates of Magnaporthe oryzae (abbreviated M. oryzae) collected from Northeast China. There were sixteen amino acid differences between the Pi65 resistance and susceptible alleles. Compared with the Pi65-resistant allele, the susceptible allele exhibited one LRR domain deletion. Pi65 was constitutively expressed in whole plants, and it could be induced in the early stage of M. oryzae infection. Transcriptome analysis revealed that numerous genes associated with disease resistance were specifically upregulated in GY129 24 h post inoculation (HPI); in contrast, photosynthesis and carbohydrate metabolism-related genes were particularly downregulated at 24 HPI, demonstrating that disease resistance-associated genes were activated in GY129 (carrying Pi65) after rice blast fungal infection and that cellular basal metabolism and energy metabolism were inhibited simultaneously. Our study provides genetic resources for improving rice blast resistance and enriches the study of rice blast resistance mechanisms.

Targeting PINK1 Using Natural Products for the Treatment of Human Diseases.

PINK1, also known as PARK6, is a PTEN-induced putative kinase 1 that is encoded by nuclear genes. PINK1 is ubiquitously expressed and regulates mitochondrial function and mitophagy in a range of cell types. The dysregulation of PINK1 is associated with the pathogenesis and development of mitochondrial-associated disorders. Many natural products could regulate PINK1 to relieve PINK1-associated diseases. Here, we review the structure and function of PINK1, its relationship to human diseases, and the regulation of natural products to PINK1. We further highlight that the discovery of natural PINK1 regulators represents an attractive strategy for the treatment of PINK1-related diseases, including liver and heart diseases, cancer, and Parkinson's disease. Moreover, investigating PINK1 regulation of natural products can enhance the in-depth comprehension of the mechanism of action of natural products.

Characterization of wall-associated kinase/wall-associated kinase-like (WAK/WAKL) family in rose (Rosa chinensis) reveals the role of RcWAK4 in Botrytis resistance.

BACKGROUND: Wall-associated kinase (WAK)/WAK-like (WAKL) is one of the subfamily of receptor like kinases (RLK). Although previous studies reported that WAK/WAKL played an important role in plant cell elongation, response to biotic and abiotic stresses, there are no systematic studies on RcWAK/RcWAKL in rose. RESULTS: In this study, we identified a total of 68 RcWAK/RcWAKL gene family members within rose (Rosa chinensis) genome. The RcWAKs contained the extracellular galacturonan-binding domain and calcium-binding epidermal growth factor (EGF)-like domain, as well as an intracellular kinase domains. The RcWAKLs are missing either calcium-binding EGF-like domain or the galacturonan-binding domain in their extracellular region. The phylogenetic analysis showed the RcWAK/RcWAKL gene family has been divided into five groups, and these RcWAK/RcWAKL genes were unevenly distributed on the 7 chromosomes of rose. 12 of RcWAK/RcWAKL genes were significantly up-regulated by Botrytis cinerea-inoculated rose petals, where RcWAK4 was the most strongly expressed. Virus induced gene silencing of RcWAK4 increased the rose petal sensitivity to B. cinerea. The results indicated RcWAK4 is involved in the resistance of rose petal against B. cinerea. CONCLUSION: Our study provides useful information to further investigate the function of the RcWAK/RcWAKL gene family and breeding research for resistance to B. cinerea in rose.

Two component system CpxR/A regulates the prodigiosin biosynthesis by negative control in Serratia marcescens FS14.

Prodigiosin is a tripyrrole red secondary metabolite synthesized by many microorganisms, including Serratia marcescens. In this study, we found that the deletion of the gene of sensor kinase CpxA dramatically decreased the prodigiosin production, while the deletion of the gene of the response regulator CpxR or both genes of CpxRA has no effect on prodigiosin production, the kinase function of CpxA is not essential for its regulation on prodigiosin production while the phosphorylation site of CpxR is required. We further demonstrated that the CpxA regulates the prodigiosin biosynthesis at the transcriptional level and the phosphatase activity of CpxA plays vital roles in the regulation of prodigiosin biosynthesis. Finally, we proposed that CpxR/A regulates the prodigiosin biosynthesis by negative control and the phosphorylation level of CpxR may determine the positive or negative control of the genes it regulated.

Oligomerization-driven MLKL ubiquitylation antagonizes necroptosis.

Mixed lineage kinase domain-like (MLKL) is the executioner in the caspase-independent form of programmed cell death called necroptosis. Receptor-interacting serine/threonine protein kinase 3 (RIPK3) phosphorylates MLKL, triggering MLKL oligomerization, membrane translocation and membrane disruption. MLKL also undergoes ubiquitylation during necroptosis, yet neither the mechanism nor the significance of this event has been demonstrated. Here, we show that necroptosis-specific multi-mono-ubiquitylation of MLKL occurs following its activation and oligomerization. Ubiquitylated MLKL accumulates in a digitonin-insoluble cell fraction comprising organellar and plasma membranes and protein aggregates. Appearance of this ubiquitylated MLKL form can be reduced by expression of a plasma membrane-located deubiquitylating enzyme. Oligomerization-induced MLKL ubiquitylation occurs on at least four separate lysine residues and correlates with its proteasome- and lysosome-dependent turnover. Using a MLKL-DUB fusion strategy, we show that constitutive removal of ubiquitin from MLKL licences MLKL auto-activation independent of necroptosis signalling in mouse and human cells. Therefore, in addition to the role of ubiquitylation in the kinetic regulation of MLKL-induced death following an exogenous necroptotic stimulus, it also contributes to restraining basal levels of activated MLKL to avoid unwanted cell death.

CsCDPK6, a CsSAMS1-Interacting Protein, Affects Polyamine/Ethylene Biosynthesis in Cucumber and Enhances Salt Tolerance by Overexpression in Tobacco.

S-adenosylmethionine synthetase (SAMS) plays a crucial role in regulating stress responses. In a recent study, we found that overexpression of the cucumber gene CsSAMS1 in tobacco can affect the production of polyamines and ethylene, as well as enhancing the salt stress tolerance of tobacco, but the exact underlying mechanisms are elusive. The calcium-dependent protein kinase (CDPK) family is ubiquitous in plants and performs different biological functions in plant development and response to abiotic stress. We used a yeast two-hybrid system to detect whether the protein CDPK6 could interact with SAMS1 and verified their interaction by bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) assays. To further explore the function of cucumber CDPK6, we isolated and characterized CsCDPK6 in cucumber. CsCDPK6 is a membrane protein that is highly expressed under various abiotic stresses, including salt stress. It was also observed that ectopic overexpression of CsCDPK6 in tobacco enhanced salt tolerance. Under salt stress, CsCDPK6-overexpressing lines enhanced the survival rate and reduced stomatal apertures in comparison to wild-type (WT) lines, as well as lowering malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents and causing less relative electrolyte leakage. Moreover, repression of CsCDPK6 expression by virus-induced gene silencing (VIGS) in cucumber seedling cotyledons under salt stress increased ethylene production and promoted the transformation from putrescine (Put) to spermidine (Spd) and spermine (Spm). These findings shed light on the interaction of CsSAMS1 and CsCDPK6, which functions positively to regulate salt stress in plants.

Rhoptry kinase protein 39 (ROP39) is a novel factor that recruits host mitochondria to the parasitophorous vacuole of Toxoplasma gondii.

Most intracellular pathogens replicate in a vacuole to avoid the defense system of the host. A few pathogens recruit host mitochondria around those vacuoles, but the molecules responsible for mitochondrial recruitment remain unidentified. It is only in the apicomplexan parasite Toxoplasma gondii, that mitochondrial association factor 1b (MAF1b) has been identified as an association factor for host mitochondria. Here, we show that rhoptry kinase family protein 39 (ROP39) induces host mitochondrial recruitment in T. gondii. We found that the abundance of ROP39 was increased on host mitochondria extracted from human foreskin fibroblasts (HFFs) infected with T. gondii. ROP39 expressed exogenously in HFFs localized on host mitochondria, indicating that it has the potential to bind to host mitochondria without assistance from other parasite factors. Confocal microscopy revealed that ROP39 colocalized with host mitochondria on the membrane of parasitophorous vacuoles, in which the parasites reside. Moreover, we observed about a 10% reduction in the level of mitochondrial association in rop39-knockout parasites compared with a parental strain.

Motility control through an anti-activation mechanism in Agrobacterium tumefaciens.

Many bacteria can migrate from a free-living, planktonic state to an attached, biofilm existence. One factor regulating this transition in the facultative plant pathogen Agrobacterium tumefaciens is the ExoR-ChvG-ChvI system. Periplasmic ExoR regulates the activity of the ChvG-ChvI two-component system in response to environmental stress, most notably low pH. ChvI impacts hundreds of genes, including those required for type VI secretion, virulence, biofilm formation, and flagellar motility. Previous studies revealed that activated ChvG-ChvI represses expression of most of class II and class III flagellar biogenesis genes, but not the master motility regulator genes visN, visR, and rem. In this study, we characterized the integration of the ExoR-ChvG-ChvI and VisNR-Rem pathways. We isolated motile suppressors of the non-motile ΔexoR mutant and thereby identified the previously unannotated mirA gene encoding a 76 amino acid protein. We report that the MirA protein interacts directly with the Rem DNA-binding domain, sequestering Rem and preventing motility gene activation. The ChvG-ChvI pathway activates mirA expression and elevated mirA is sufficient to block motility. This study reveals how the ExoR-ChvG-ChvI pathway prevents flagellar motility in A. tumefaciens. MirA is also conserved among other members of the Rhizobiales suggesting similar mechanisms of motility regulation.

Evolutionary analysis and functional characterization of SiBRI1 as a Brassinosteroid receptor gene in foxtail millet.

Brassinosteroids (BRs) play important roles in plant growth and development. Although BR receptors have been intensively studied in Arabidopsis, those in foxtail millet remain largely unknown. Here, we show that the BR signaling function of BRASSINOSTEROID INSENSITIVE 1 (BRI1) is conserved between Arabidopsis and foxtail millet, a new model species for C4 and Panicoideae grasses. We identified four putative BR receptor genes in the foxtail millet genome: SiBRI1, SiBRI1-LIKE RECEPTOR KINASE 1 (SiBRL1), SiBRL2 and SiBRL3. Phylogenetic analysis was used to classify the BR receptors in dicots and monocots into three branches. Analysis of their expression patterns by quantitative real-time PCR (qRT-PCR) showed that these receptors were ubiquitously expressed in leaves, stems, dark-grown seedlings, roots and non-flowering spikelets. GFP fusion experiments verified that SiBRI1 localized to the cell membrane. We also explored the SiBRI1 function in Arabidopsis through complementation experiments. Ectopic overexpression of SiBRI1 in an Arabidopsis BR receptor loss-of-function mutant, bri1-116, mostly reversed the developmental defects of the mutant. When SiBRI1 was overexpressed in foxtail millet, the plants showed a drooping leaf phenotype and root development inhibition, lateral root initiation inhibition, and the expression of BR synthesis genes was inhibited. We further identified BRI1-interacting proteins by immunoprecipitation (IP)-mass spectrometry (MS). Our results not only demonstrate that SiBRI1 plays a conserved role in BR signaling in foxtail millet but also provide insight into the molecular mechanism of SiBRI1.

Necroptosis protects against exacerbation of acute pancreatitis.

The sensing of various extrinsic stimuli triggers the receptor-interacting protein kinase-3 (RIPK3)-mediated signaling pathway, which leads to mixed-lineage kinase-like (MLKL) phosphorylation followed by necroptosis. Although necroptosis is a form of cell death and is involved in inflammatory conditions, the roles of necroptosis in acute pancreatitis (AP) remain unclear. In the current study, we administered caerulein to Ripk3- or Mlkl-deficient mice (Ripk3-/- or Mlkl-/- mice, respectively) and assessed the roles of necroptosis in AP. We found that Ripk3-/- mice had significantly more severe pancreatic edema and inflammation associated with macrophage and neutrophil infiltration than control mice. Consistently, Mlkl-/- mice were more susceptible to caerulein-induced AP, which occurred in a time- and dose-dependent manner, than control mice. Mlkl-/- mice exhibit weight loss, edematous pancreatitis, necrotizing pancreatitis, and acinar cell dedifferentiation in response to tissue damage. Genetic deletion of Mlkl resulted in downregulation of the antiapoptotic genes Bclxl and Cflar in association with increases in the numbers of apoptotic cells, as detected by TUNEL assay. These findings suggest that RIPK3 and MLKL-mediated necroptosis exerts protective effects in AP and caution against the use of necroptosis inhibitors for AP treatment.

RIP1-Mediated Necroptosis Facilitates Oxidative Stress‒Induced Melanocyte Death, Offering Insight into Vitiligo.

Vitiligo is a common depigmentation disease characterized by melanocyte death, which is attributed to various mechanisms such as apoptosis and autoimmune destruction. However, whether necroptosis, a newly discovered way of cell death, plays a key role in the pathogenesis of vitiligo is still elusive and has not been well-studied. In this study, we found that necroptosis markers, including phosphorylated RIP3 and phosphorylated-MLKL, were positive in melanocytes from vitiligo perilesional skin, which supported the existence of necroptosis in vitiligo. Furthermore, the expression of RIP1 was remarkably upregulated in melanocytes treated with hydrogen peroxide. Then, RIP1 intervention suppression and MLKL deficiency could significantly enhance the resistance of melanocytes to hydrogen peroxide‒induced necroptosis. Mechanistically, we confirmed that RIP1 and RIP3 could form necrosomes under oxidative stress and further trigger phosphorylated MLKL translocation to the cell membrane, which led to the destruction of melanocytes. Finally, we showed that RIP1-mediated generation of mitochondrial ROS contributed to necrosome formation in melanocytes. Collectively, our study confirms that necroptosis significantly facilitates oxidative stress‒induced melanocyte death through the RIP1 signaling pathway, offering insight into vitiligo.

The receptor-like cytoplasmic kinase RIPK regulates broad-spectrum ROS signaling in multiple layers of plant immune system.

Production of reactive oxygen species (ROS) via the activity of respiratory burst oxidase homologs (RBOHs) plays a vital role in multiple layers of the plant immune system, including pathogen-associated molecular pattern-triggered immunity (PTI), damage-associated molecular pattern-triggered immunity (DTI), effector-triggered immunity (ETI), and systemic acquired resistance (SAR). It is generally established that RBOHD is activated by different receptor-like cytoplasmic kinases (RLCKs) in response to various immune elicitors. In this study, we showed that RPM1-INDUCED PROTEIN KINASE (RIPK), an RLCK VII subfamily member, contributes to ROS production in multiple layers of plant immune system. The ripk mutants showed reduced ROS production in response to treatment with all examined immune elicitors that trigger PTI, DTI, ETI, and SAR. We found that RIPK can directly phosphorylate the N-terminal region of RBOHD in vitro, and the levels of phosphorylated S343/S347 residues of RBOHD are sigfniciantly lower in ripk mutants compared with the wild type upon treatment with all tested immune elicitors. We further demonstrated that phosphorylation of RIPK is required for its function in regulating RBOHD-mediated ROS production. Similar to rbohd, ripk mutants showed reduced stomatal closure and impaired SAR, and were susceptible to the necrotrophic bacterium Pectobacterium carotovorum. Collectively, our results indicate that RIPK regulates broad-spectrum RBOHD-mediated ROS signaling during PTI, DTI, ETI, and SAR, leading to subsequent RBOHD-dependent immune responses.

Wheat Pm4 resistance to powdery mildew is controlled by alternative splice variants encoding chimeric proteins.

Crop breeding for resistance to pathogens largely relies on genes encoding receptors that confer race-specific immunity. Here, we report the identification of the wheat Pm4 race-specific resistance gene to powdery mildew. Pm4 encodes a putative chimeric protein of a serine/threonine kinase and multiple C2 domains and transmembrane regions, a unique domain architecture among known resistance proteins. Pm4 undergoes constitutive alternative splicing, generating two isoforms with different protein domain topologies that are both essential for resistance function. Both isoforms interact and localize to the endoplasmatic reticulum when co-expressed. Pm4 reveals additional diversity of immune receptor architecture to be explored for breeding and suggests an endoplasmatic reticulum-based molecular mechanism of Pm4-mediated race-specific resistance.

C. elegans discriminates colors to guide foraging.

Color detection is used by animals of diverse phyla to navigate colorful natural environments and is thought to require evolutionarily conserved opsin photoreceptor genes. We report that Caenorhabditis elegans roundworms can discriminate between colors despite the fact that they lack eyes and opsins. Specifically, we found that white light guides C. elegans foraging decisions away from a blue-pigment toxin secreted by harmful bacteria. These foraging decisions are guided by specific blue-to-amber ratios of light. The color specificity of color-dependent foraging varies notably among wild C. elegans strains, which indicates that color discrimination is ecologically important. We identified two evolutionarily conserved cellular stress response genes required for opsin-independent, color-dependent foraging by C. elegans, and we speculate that cellular stress response pathways can mediate spectral discrimination by photosensitive cells and organisms-even by those lacking opsins.

MLKL inhibits intestinal tumorigenesis by suppressing STAT3 signaling pathway.

Mixed lineage kinase domain-like protein (MLKL) plays an important role in necroptosis, but the role and mechanism of MLKL in intestinal tumorigenesis remain unclear. Here, we found that hematopoietic- and nonhematopoietic-derived MLKL affected intestinal inflammation, but nonhematopoietic-derived MLKL primarily inhibited intestinal tumorigenesis. Loss of MLKL enhanced intestinal regeneration and the susceptibility to intestinal tumorigenesis in Apcmin/+ mice by hyperactivating the Janus kinase 2 (JAK2)/ signal transducer and activator of transcription 3 (STAT3) axis. Furthermore, MLKL deficiency increased interleukin-6 (IL-6) production in dendritic cells. Administration of anti-IL-6R antibody therapy reduced intestinal tumorigenesis in Apcmin/+Mlkl-/- mice. Notably, low MLKL expression in human colorectal tumors, which enhanced STAT3 activation, was associated with decreased overall survival. Together, our results reveal that MLKL exhibits a suppressive effect during intestinal tumorigenesis by suppressing the IL-6/JAK2/STAT3 signals.

MLKL: Functions beyond serving as the Executioner of Necroptosis.

Recently, necroptosis, as a programmed cell death pathway, has drawn much attention as it has been implicated in multiple pathologies, especially in the field of inflammatory diseases. Pseudokinase mixed lineage kinase domain-like protein (MLKL) serves as a terminal-known obligate effector in the process of necroptosis. To date, the majority of research on MLKL has focused on its role in necroptosis, and the prevailing view has been that the sole function of MLKL is to mediate necroptosis. However, increasing evidence indicates that MLKL can serve as a regulator of many diseases via its non-necroptotic functions. These functions of MLKL shed light on its functional complexity and diversity. In this review, we briefly introduce the current state of knowledge regarding the structure of MLKL, necroptosis signaling, as well as cross-linkages among necroptosis and other regulated cell death pathways, and we particularly highlight recent progress related to newly identified functions and inhibitors of MLKL. These discussions promote a better understanding of the role of MLKL in diseases, which will foster efforts to pharmacologically target this molecule in clinical treatments.