Flavonol-mediated stabilization of PIN efflux complexes regulates polar auxin transport.

The transport of auxin controls the rate, direction and localization of plant growth and development. The course of auxin transport is defined by the polar subcellular localization of the PIN proteins, a family of auxin efflux transporters. However, little is known about the composition and regulation of the PIN protein complex. Here, using blue-native PAGE and quantitative mass spectrometry, we identify native PIN core transport units as homo- and heteromers assembled from PIN1, PIN2, PIN3, PIN4 and PIN7 subunits only. Furthermore, we show that endogenous flavonols stabilize PIN dimers to regulate auxin efflux in the same way as does the auxin transport inhibitor 1-naphthylphthalamic acid (NPA). This inhibitory mechanism is counteracted both by the natural auxin indole-3-acetic acid and by phosphomimetic amino acids introduced into the PIN1 cytoplasmic domain. Our results lend mechanistic insights into an endogenous control mechanism which regulates PIN function and opens the way for a deeper understanding of the protein environment and regulation of the polar auxin transport complex.

Glutathione and neodiosmin feedback sustain plant immunity.

Plants have evolved a two-layer immune system comprising pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) that is activated in response to pathogen invasion. Microbial patterns and pathogen effectors can be recognized by surface-localized pattern-recognition receptors (PRRs) and intracellularly localized nucleotide-binding leucine-rich repeat receptors (NLRs) to trigger PTI and ETI responses, respectively. At present, the metabolites activated by PTI and ETI and their roles and signalling pathways in plant immunity are not well understood. In this study, metabolomic analysis showed that ETI and PTI induced various flavonoids and amino acids and their derivatives in plants. Interestingly, both glutathione and neodiosmin content were specifically up-regulated by ETI and PTI, respectively, which significantly enhanced plant immunity. Further studies showed that glutathione and neodiosmin failed to induce a plant immune response in which PRRs/co-receptors were mutated. In addition, glutathione-reduced mutant gsh1 analysis showed that GSH1 is also required for PTI and ETI. Finally, we propose a model in which glutathione and neodiosmin are considered signature metabolites induced in the process of ETI and PTI activation in plants and further continuous enhancement of plant immunity in which PRRs/co-receptors are needed. This model is beneficial for an in-depth understanding of the closed-loop mode of the positive feedback regulation of PTI and ETI signals at the metabolic level.

Serratia marcescens PLR enhances lateral root formation through supplying PLR-derived auxin and enhancing auxin biosynthesis in Arabidopsis.

Plant growth promoting rhizobacteria (PGPR) refer to bacteria that colonize the rhizosphere and contribute to plant growth or stress tolerance. To further understand the molecular mechanism by which PGPR exhibit symbiosis with plants, we performed a high-throughput single colony screening from the rhizosphere, and uncovered a bacterium (named promoting lateral root, PLR) that significantly promotes Arabidopsis lateral root formation. By 16S rDNA sequencing, PLR was identified as a novel sub-species of Serratia marcescens. RNA-seq analysis of Arabidopsis integrated with phenotypic verification of auxin signalling mutants demonstrated that the promoting effect of PLR on lateral root formation is dependent on auxin signalling. Furthermore, PLR enhanced tryptophan-dependent indole-3-acetic acid (IAA) synthesis by inducing multiple auxin biosynthesis genes in Arabidopsis. Genome-wide sequencing of PLR integrated with the identification of IAA and its precursors in PLR exudates showed that tryptophan treatment significantly enhanced the ability of PLR to produce IAA and its precursors. Interestingly, PLR induced the expression of multiple nutrient (N, P, K, S) transporter genes in Arabidopsis in an auxin-independent manner. This study provides evidence of how PLR enhances plant growth through fine-tuning auxin biosynthesis and signalling in Arabidopsis, implying a potential application of PLR in crop yield improvement through accelerating root development.

The role of AUX1 during lateral root development in the domestication of the model C4 grass Setaria italica.

C4 photosynthesis increases the efficiency of carbon fixation by spatially separating high concentrations of molecular oxygen from Rubisco. The specialized leaf anatomy required for this separation evolved independently many times. The morphology of C4 root systems is also distinctive and adapted to support high rates of photosynthesis; however, little is known about the molecular mechanisms that have driven the evolution of C4 root system architecture. Using a mutant screen in the C4 model plant Setaria italica, we identify Siaux1-1 and Siaux1-2 as root system architecture mutants. Unlike in S. viridis, AUX1 promotes lateral root development in S. italica. A cell by cell analysis of the Siaux1-1 root apical meristem revealed changes in the distribution of cell volumes in all cell layers and a dependence of the frequency of protophloem and protoxylem strands on SiAUX1. We explore the molecular basis of the role of SiAUX1 in seedling development using an RNAseq analysis of wild-type and Siaux1-1 plants and present novel targets for SiAUX1-dependent gene regulation. Using a selection sweep and haplotype analysis of SiAUX1, we show that Hap-2412TT in the promoter region of SiAUX1 is an allele which is associated with lateral root number and has been strongly selected for during Setaria domestication.

CDC48B facilitates the intercellular trafficking of SHORT-ROOT during radial patterning in roots.

CELL DIVISION CONTROL PROTEIN48 (CDC48) is essential for membrane fusion, protein degradation, and other cellular processes. Here, we revealed the crucial role of CDC48B in regulating periclinal cell division in roots by analyzing the recessive gen1 mutant. We identified the GEN1 gene through map-based cloning and verified that GEN1 encodes CDC48B. gen1 showed severely inhibited root growth, increased periclinal cell division in the endodermis, defective middle cortex (MC) formation, and altered ground tissue patterning in roots. Consistent with these phenotypes, CYCLIND 6;1(CYCD6;1), a periclinal cell division marker, was upregulated in gen1 compared to Col-0. The ratio of SHRpro :SHR-GFP fluorescence in pre-dividing nuclei versus the adjacent stele decreased by 33% in gen1, indicating that the trafficking of SHORT-ROOT (SHR) decreased in gen1 when endodermal cells started to divide. These findings suggest that the loss of function of CDC48B inhibits the intercellular trafficking of SHR from the stele to the endodermis, thereby decreasing SHR accumulation in the endodermis. These findings shed light on the crucial role of CDC48B in regulating periclinal cell division in roots.

The unconventional prefoldin RPB5 interactor mediates the gravitropic response by modulating cytoskeleton organization and auxin transport in Arabidopsis.

Gravity-induced root curvature involves the asymmetric distribution of the phytohormone auxin. This response depends on the concerted activities of the auxin transporters such as PIN-FORMED (PIN) proteins for auxin efflux and AUXIN RESISTANT 1 (AUX1) for auxin influx. However, how the auxin gradient is established remains elusive. Here we identified a new mutant with a short root, strong auxin distribution in the lateral root cap and an impaired gravitropic response. The causal gene encoded an Arabidopsis homolog of the human unconventional prefoldin RPB5 interactor (URI). AtURI interacted with prefoldin 2 (PFD2) and PFD6, two ß-type PFD members that modulate actin and tubulin patterning in roots. The auxin reporter DR5rev :GFP showed that asymmetric auxin redistribution after gravistimulation is disordered in aturi-1 root tips. Treatment with the endomembrane protein trafficking inhibitor brefeldin A indicated that recycling of the auxin transporter PIN2 is disrupted in aturi-1 roots as well as in pfd mutants. We propose that AtURI cooperates with PFDs to recycle PIN2 and modulate auxin distribution.

Improvement of host-induced gene silencing efficiency via polycistronic-tRNA-amiR expression for multiple target genes and characterization of RNAi mechanism in Mythimna separata.

Host-induced gene silencing (HIGS) emerged as a new strategy for pest control. However, RNAi efficiency is reported to be low in Lepidoptera, which are composed of many important crop pests. To address this, we generated transgenic plants to develop HIGS effects in a maize pest, Mythimna separata (Lepidoptera, Noctuidae), by targeting chitinase encoding genes. More importantly, we developed an artificial microRNA (amiR) based PTA (polycistronic-tRNA-amiR) system for silencing multiple target genes. Compared with hpRNA (hairpin RNA), transgenic expression of a PTA cassette including an amiR for the gut-specific dsRNA nuclease gene MsREase, resulted in improved knockdown efficiency and caused more pronounced developmental abnormalities in recipient insects. When target gene siRNAs were analysed after HIGS and direct dsRNA/siRNA feeding, common features such as sense polarity and siRNA hotspot regions were observed, however, they differed in siRNA transitivity and major 20-24nt siRNA species. Core RNAi genes were identified in M. separata, and biochemical activities of MsAGO2, MsSID1 and MsDcr2 were confirmed by EMSA (electrophoretic mobility shift assay) and dsRNA cleavage assays, respectively. Taken together, we provide compelling evidence for the existence of the RNAi mechanism in M. separata by analysis of both siRNA signatures and RNAi machinery components, and the PTA system could potentially be useful for future RNAi control of lepidopteran pests.

Primary root and root hair development regulation by OsAUX4 and its participation in the phosphate starvation response.

Among the five members of AUX1/LAX genes coding for auxin carriers in rice, only OsAUX1 and OsAUX3 have been reported. To understand the function of the other AUX1/LAX genes, two independent alleles of osaux4 mutants, osaux4-1 and osaux4-2, were constructed using the CRISPR/Cas9 editing system. Homozygous osaux4-1 or osaux4-2 exhibited shorter primary root (PR) and longer root hair (RH) compared to the wild-type Dongjin (WT/DJ), and lost response to indoleacetic acid (IAA) treatment. OsAUX4 is intensively expressed in roots and localized on the plasma membrane, suggesting that OsAUX4 might function in the regulation of root development. The decreased meristem cell division activity and the downregulated expression of cell cycle genes in root apices of osaux4 mutants supported the hypothesis that OsAUX4 positively regulates PR elongation. OsAUX4 is expressed in RH, and osaux4 mutants showing longer RH compared to WT/DJ implies that OsAUX4 negatively regulates RH development. Furthermore, osaux4 mutants are insensitive to Pi starvation (-Pi) and OsAUX4 effects on the -Pi response is associated with altered expression levels of Pi starvation-regulated genes, and auxin distribution/contents. This study revealed that OsAUX4 not only regulates PR and RH development but also plays a regulatory role in crosstalk between auxin and -Pi signaling.

AtNSF regulates leaf serration by modulating intracellular trafficking of PIN1 in Arabidopsis thaliana.

In eukaryotes, N-ethylmaleimide-sensitive factor (NSF) is a conserved AAA+ ATPase and a key component of the membrane trafficking machinery that promotes the fusion of secretory vesicles with target membranes. Here, we demonstrate that the Arabidopsis thaliana genome contains a single copy of NSF, AtNSF, which plays an essential role in the regulation of leaf serration. The AtNSF knock-down mutant, atnsf-1, exhibited more serrations in the leaf margin. Moreover, polar localization of the PIN-FORMED1 (PIN1) auxin efflux transporter was diffuse around the margins of atnsf-1 leaves and root growth was inhibited in the atnsf-1 mutant. More PIN1-GFP accumulated in the intracellular compartments of atnsf-1 plants, suggesting that AtNSF is required for intracellular trafficking of PIN between the endosome and plasma membrane. Furthermore, the serration phenotype was suppressed in the atnsf-1 pin1-8 double mutant, suggesting that AtNSF is required for PIN1-mediated polar auxin transport to regulate leaf serration. The CUP-SHAPED COTYLEDON2 (CUC2) transcription factor gene is up-regulated in atnsf-1 plants and the cuc2-3 single mutant exhibits smooth leaf margins, demonstrating that AtNSF also functions in the CUC2 pathway. Our results reveal that AtNSF regulates the PIN1-generated auxin maxima with a CUC2-mediated feedback loop to control leaf serration. This article is protected by copyright. All rights reserved.

What Is the Most Reliable Classification System to Assess Tibial Pilon Fractures?

The aim of this study was to assess inter- and intraobserver agreement of the traditional systems (Ruedi-Allgower, AO [Arbeitsgemeinschaft für Osteosynthesefragen], and Topliss) and the newly proposed Leonetti classification system of pilon fractures. We studied all patients at our center who underwent pilon fracture surgery over a 2-year period: 68 patients (70 legs) were included. Four observers independently classified each pilon fracture according to the Ruedi-Allgower, AO, Topliss, and Leonetti systems by evaluating radiographs and computed tomography images on 2 occasions. The inter- and intraobserver agreements were calculated using the Fleiss kappa test. Interobserver reliability was good for AO types (A, B, and C) and Ruedi-Allgower (κ = 0.71 and 0.61, respectively), whereas the interobserver reliability was moderate for AO groups (A1, A2, A3, B1, B2, B3, C1, C2, and C3), Topliss families, Topliss subfamilies, Leonetti types, and Leonetti subtypes. Intraobserver reproducibility was excellent for the Ruedi-Allgower classification, AO types, and Topliss families and good for AO groups, Topliss subfamilies, and Leonetti types and subtypes. Ruedi-Allgower and AO classification systems are the most reliable among those currently used for pilon fractures, but with lower agreement at the AO group level. The use of Topliss and Leonetti classification systems is not recommended because of less favorable results.

Prognostic role of PD-L1 for HCC patients after potentially curative resection: a meta-analysis.

BACKGROUND: A series of studies has investigated the prognostic role and clinical significance of programmed death ligand 1 (PD-L1) in hepatocellular carcinoma (HCC). However, the results were inconsistent. We aimed to clarify the prognostic role of PD-L1 and relationship between PD-L1 expression and several important clinicopathological features. METHODS: PubMed, EMBASE and the Science Citation Index Expanded were systematically searched. All cohort or case-control studies comparing the prognosis and clinical features between the high PD-L1 and low PD-L1 groups were included. Publication bias was evaluated using funnel plots and Begg's test. Subgroup analysis, sensitivity analysis and meta-regression analysis were performed. RESULTS: Seventeen studies including 2979 patients were eligible. The overall survival (OS) was not significantly different between the high and low PD-L1 groups (hazard ratio [HR]: 1.27; 95% confidence interval [CI] 0.98-1.65: P = 0.07) with significant heterogeneity (P < 0.001; I2 = 81%). The recurrence-free survival (RFS) was not significantly different between the high and low PD-L1 groups (HR: 1.22; 95% CI 0.97-1.53; P = 0.09) with significant heterogeneity (P < 0.001; I2 = 78%). The expression of PD-L1 was found to be significantly correlated with alpha-fetoprotein, hepatitis history, and tumour-infiltrating lymphocytes. Begg's test found no significant publication bias for OS and RFS. Sensitivity analysis established the robustness of our results. Subgroup analysis and meta-regression analysis found the region of research as a significant contributor to inter-study heterogeneity in RFS, indicating some racial differences in the prognostic role of PD-L1. CONCLUSIONS: Our study found no significant prognostic role of PD-L1 in HCC patients after potential curative hepatectomy based on our included studies. The expression of PD-L1 was significantly correlated with AFP, hepatitis history, and TILs. The prognostic role of PD-L1 in HCC warrants further investigation.

A P-Loop NTPase Regulates Quiescent Center Cell Division and Distal Stem Cell Identity through the Regulation of ROS Homeostasis in Arabidopsis Root.

Reactive oxygen species (ROS) are recognized as important regulators of cell division and differentiation. The Arabidopsis thaliana P-loop NTPase encoded by APP1 affects root stem cell niche identity through its control of local ROS homeostasis. The disruption of APP1 is accompanied by a reduction in ROS level, a rise in the rate of cell division in the quiescent center (QC) and the promotion of root distal stem cell (DSC) differentiation. Both the higher level of ROS induced in the app1 mutant by exposure to methyl viologen (MV), and treatment with hydrogen peroxide (H2O2) rescued the mutant phenotype, implying that both the increased rate of cell division in the QC and the enhancement in root DSC differentiation can be attributed to a low level of ROS. APP1 is expressed in the root apical meristem cell mitochondria, and its product is associated with ATP hydrolase activity. The key transcription factors, which are defining root distal stem niche, such as SCARECROW (SCR) and SHORT ROOT (SHR) are both significantly down-regulated at both the transcriptional and protein level in the app1 mutant, indicating that SHR and SCR are important downstream targets of APP1-regulated ROS signaling to control the identity of root QC and DSCs.

Characterization of auxin transporter PIN6 plasma membrane targeting reveals a function for PIN6 in plant bolting.

Auxin gradients are sustained by series of influx and efflux carriers whose subcellular localization is sensitive to both exogenous and endogenous factors. Recently the localization of the Arabidopsis thaliana auxin efflux carrier PIN-FORMED (PIN) 6 was reported to be tissue-specific and regulated through unknown mechanisms. Here, we used genetic, molecular and pharmacological approaches to characterize the molecular mechanism(s) controlling the subcellular localization of PIN6. PIN6 localizes to endomembrane domains in tissues with low PIN6 expression levels such as roots, but localizes at the plasma membrane (PM) in tissues with increased PIN6 expression such as the inflorescence stem and nectary glands. We provide evidence that this dual localization is controlled by PIN6 phosphorylation and demonstrate that PIN6 is phosphorylated by mitogen-activated protein kinases (MAPKs) MPK4 and MPK6. The analysis of transgenic plants expressing PIN6 at PM or in endomembrane domains reveals that PIN6 subcellular localization is critical for Arabidopsis inflorescence stem elongation post-flowering (bolting). In line with a role for PIN6 in plant bolting, inflorescence stems elongate faster in pin6 mutant plants than in wild-type plants. We propose that PIN6 subcellular localization is under the control of developmental signals acting on tissue-specific determinants controlling PIN6-expression levels and PIN6 phosphorylation.

Plastid-localized glutathione reductase2-regulated glutathione redox status is essential for Arabidopsis root apical meristem maintenance.

Glutathione is involved in thiol redox signaling and acts as a major redox buffer against reactive oxygen species, helping to maintain a reducing environment in vivo. Glutathione reductase (GR) catalyzes the reduction of glutathione disulfide (GSSG) into reduced glutathione (GSH). The Arabidopsis thaliana genome encodes two GRs: GR1 and GR2. Whereas the cytosolic/peroxisomal GR1 is not crucial for plant development, we show here that the plastid-localized GR2 is essential for root growth and root apical meristem (RAM) maintenance. We identify a GR2 mutant, miao, that displays strong inhibition of root growth and severe defects in the RAM, with GR activity being reduced to ∼50%. miao accumulates high levels of GSSG and exhibits increased glutathione oxidation. The exogenous application of GSH or the thiol-reducing agent DTT can rescue the root phenotype of miao, demonstrating that the RAM defects in miao are triggered by glutathione oxidation. Our in silico analysis of public microarray data shows that auxin and glutathione redox signaling generally act independently at the transcriptional level. We propose that glutathione redox status is essential for RAM maintenance through both auxin/PLETHORA (PLT)-dependent and auxin/PLT-independent redox signaling pathways.

The basic helix-loop-helix transcription factor MYC2 directly represses PLETHORA expression during jasmonate-mediated modulation of the root stem cell niche in Arabidopsis.

The root stem cell niche, which in the Arabidopsis thaliana root meristem is an area of four mitotically inactive quiescent cells (QCs) and the surrounding mitotically active stem cells, is critical for root development and growth. We report here that during jasmonate-induced inhibition of primary root growth, jasmonate reduces root meristem activity and leads to irregular QC division and columella stem cell differentiation. Consistently, jasmonate reduces the expression levels of the AP2-domain transcription factors PLETHORA1 (PLT1) and PLT2, which form a developmentally instructive protein gradient and mediate auxin-induced regulation of stem cell niche maintenance. Not surprisingly, the effects of jasmonate on root stem cell niche maintenance and PLT expression require the functioning of MYC2/JASMONATE INSENSITIVE1, a basic helix-loop-helix transcription factor that involves versatile aspects of jasmonate-regulated gene expression. Gel shift and chromatin immunoprecipitation experiments reveal that MYC2 directly binds the promoters of PLT1 and PLT2 and represses their expression. We propose that MYC2-mediated repression of PLT expression integrates jasmonate action into the auxin pathway in regulating root meristem activity and stem cell niche maintenance. This study illustrates a molecular framework for jasmonate-induced inhibition of root growth through interaction with the growth regulator auxin.

BLOS1, a putative BLOC-1 subunit, interacts with SNX1 and modulates root growth in Arabidopsis.

Internalization and sorting of macromolecules are inherent properties of all eukaryotic cells that are achieved by vesicle trafficking. However, this process is relatively less understood in plants. An eight-subunit protein complex, BLOC-1, which is involved in endosomal transport from the endosomes to the lysosomes, has been identified in both human and mice. In this study, two homologous subunits of this complex, BLOS1 (or AtGCN5L1) and BLOS2, have been characterized in Arabidopsis. Both BLOS1 and BLOS2 interacted with SNX1 on the sorting endosomes. Inducible RNAi lines with reduced levels of BLOS1 had longer primary roots and more lateral roots. Consistently, PIN1 and PIN2 were increased in BLOS1 RNAi lines, implicating an impaired transport from the endosomes to the vacuoles. These results suggest that a putative BLOC-1 complex in Arabidopsis might mediate the vacuolar degradative transport through direct interaction with SNX1 to regulate the homeostasis of PIN1 and PIN2, which is important for plant growth and development.

Honghua extract mediated potent inhibition of COVID-19 host cell pathways.

Honghua (Carthami flos) and Xihonghua (Croci stigma) have been used in anti-COVID-19 as Traditional Chinese Medicine, but the mechanism is unclear. In this study, we applied network pharmacology by analysis of active compounds and compound-targets networks, enzyme kinetics assay, signaling pathway analysis and investigated the potential mechanisms of anti-COVID-19. We found that both herbs act on signaling including kinases, response to inflammation and virus. Moreover, crocin likely has an antiviral effect due to its high affinity towards the human ACE2 receptor by simulation. The extract of Honghua and Xihonghua exhibited nanozyme/herbzyme activity of alkaline phosphatase, with distinct fluorescence. Thus, our data suggest the great potential of Honghua in the development of anti-COVID-19 agents.

The Effects of Antral Preservation and Antral Resection on Body Composition, Glycemic Control and Bone Mineral Density Following Vertical Sleeve Gastrectomy in C57BL/6J Mice with Obesity and Type 2 Diabetes.

PURPOSE: Sleeve gastrectomy (SG) is the most currently popular operation for obesity and related metabolic disorders. The aim of this study was to compare the effect of antrum preservation SG (AP-SG) and antrum resection SG (AR-SG) on the body composition, glycemic control and bone mineral density (BMD) in mice. METHODS: Sham, AP-SG and AR-SG operation were performed on obese and T2D C57BL/6J mice (8 in each group). Body weight, food intake, and fasting glucose (FG) levels were measured at the 0, 2, 4, 6 and 8 weeks post-operatively. Oral glucose tolerance test (OGTT) was performed preoperatively and at the eighth postoperative week. The body fat content and total body BMD were evaluated by dual-energy x-ray absorptiometry. After being euthanized, the femurs were harvested and analyzed by micro-CT. RESULTS: The improvements in body weight, food intake, FG, glycemic control and body fat were statistically significant following AP-SG and AR-SG. Both AP-SG and AR-SG groups decreased total body BMD and regional BMD in the distal femur compared to the sham group. No significant difference of FG was observed in AP-SG and AR-SG group postoperatively, but AR-SG showed significantly superior OGTT glucose AUC than AP-SG. Except for a lower BMD, AR-SG achieved superior outcomes in body fat and glycemic control than AP-SG. CONCLUSION: Antrum resection SG shows a lower percentage of body fat and better glycemic control than antrum preservation SG. However, antrum resection SG has a higher risk of having a lower bone mass. Further human clinical trials are needed to confirm this finding.