Dynamics of the Synechococcus elongatus cytoskeletal GTPase FtsZ yields mechanistic and evolutionary insight into cyanobacterial and chloroplast FtsZs.

The division of cyanobacteria and their chloroplast descendants is orchestrated by filamenting temperature-sensitive Z (FtsZ), a cytoskeletal GTPase that polymerizes into protofilaments that form a "Z ring" at the division site. The Z ring has both a scaffolding function for division-complex assembly and a GTPase-dependent contractile function that drives cell or organelle constriction. A single FtsZ performs these functions in bacteria, whereas in chloroplasts, they are performed by two copolymerizing FtsZs, called AtFtsZ2 and AtFtsZ1 in Arabidopsis thaliana, which promote protofilament stability and dynamics, respectively. To probe the differences between cyanobacterial and chloroplast FtsZs, we used light scattering to characterize the in vitro protofilament dynamics of FtsZ from the cyanobacterium Synechococcus elongatus PCC 7942 (SeFtsZ) and investigate how coassembly of AtFtsZ2 or AtFtsZ1 with SeFtsZ influences overall dynamics. SeFtsZ protofilaments assembled rapidly and began disassembling before GTP depletion, whereas AtFtsZ2 protofilaments were far more stable, persisting beyond GTP depletion. Coassembled SeFtsZ-AtFtsZ2 protofilaments began disassembling before GTP depletion, similar to SeFtsZ. In contrast, AtFtsZ1 did not alter disassembly onset when coassembled with SeFtsZ, but fluorescence recovery after photobleaching analysis showed it increased the turnover of SeFtsZ subunits from SeFtsZ-AtFtsZ1 protofilaments, mirroring its effect upon coassembly with AtFtsZ2. Comparisons of our findings with previous work revealed consistent differences between cyanobacterial and chloroplast FtsZ dynamics and suggest that the scaffolding and dynamics-promoting functions were partially separated during evolution of two chloroplast FtsZs from their cyanobacterial predecessor. They also suggest that chloroplasts may have evolved a mechanism distinct from that in cyanobacteria for promoting FtsZ protofilament dynamics.

Challenges and solutions: surveying researchers on what type of community engagement and involvement activities are feasible in low and middle income countries during the COVID-19 pandemic.

OBJECTIVES: Measures to limit the spread of infection during the COVID-19 global pandemic have made engaging and involving members of the community in global health research more challenging. This research aimed to explore how global health researchers adapted to the imposed pandemic measures in low and middle income countries (LMICs) and how they overcame challenges to effective community engagement and involvement (CEI). DESIGN: A qualitative two-stage mixed-methods study involving an online survey and a virtual round table. SETTING: The survey and round table were completed online. PARTICIPANTS: Of 53 participants, 43 were LMIC-based or UK-based global health researchers and/or CEI professionals, and 10 worked for the National Institute for Health Research or UK Government's Department of Health and Social Care. OUTCOME MEASURES: This study aimed to capture data on: the number of CEI activities halted and adapted because of the COVID-19 pandemic; where CEI is possible; how it has been adapted; what the challenges and successes were; and the potential impact of adapted or halted CEI on global health research. RESULTS: Pandemic control measures forced the majority of researchers to stop or amend their planned CEI activities. Most face-to-face CEI activities were replaced with remote methods, such as online communication. Virtual engagement enabled researchers to maintain already established relationships with community members, but was less effective when developing new relationships or addressing challenges around the inclusion of marginalised community groups. CONCLUSIONS: COVID-19 has highlighted the need for contingency planning and flexibility in CEI. The redesigning and adopting of remote methods has come with both advantages and disadvantages, and required new skills, access to technology, funding, reliable services and enthusiasm from stakeholders. The methods suggested have the potential to augment or substitute previously preferred CEI activities. The effectiveness and impact of these remote CEI activities need to be assessed.

The Arabidopsis thaliana chloroplast division protein FtsZ1 counterbalances FtsZ2 filament stability in vitro.

Bacterial cell and chloroplast division are driven by a contractile "Z ring" composed of the tubulin-like cytoskeletal GTPase FtsZ. Unlike bacterial Z rings, which consist of a single FtsZ, the chloroplast Z ring in plants is composed of two FtsZ proteins, FtsZ1 and FtsZ2. Both are required for chloroplast division in vivo, but their biochemical relationship is poorly understood. We used GTPase assays, light scattering, transmission electron microscopy, and sedimentation assays to investigate the assembly behavior of purified Arabidopsis thaliana (At) FtsZ1 and AtFtsZ2 both individually and together. Both proteins exhibited GTPase activity. AtFtsZ2 assembled relatively quickly, forming protofilament bundles that were exceptionally stable, as indicated by their sustained assembly and slow disassembly. AtFtsZ1 did not form detectable protofilaments on its own. When mixed with AtFtsZ2, AtFtsZ1 reduced the extent and rate of AtFtsZ2 assembly, consistent with its previously demonstrated ability to promote protofilament subunit turnover in living cells. Mixing the two FtsZ proteins did not increase the overall GTPase activity, indicating that the effect of AtFtsZ1 on AtFtsZ2 assembly was not due to a stimulation of GTPase activity. However, the GTPase activity of AtFtsZ1 was required to reduce AtFtsZ2 assembly. Truncated forms of AtFtsZ1 and AtFtsZ2 consisting of only their conserved core regions largely recapitulated the behaviors of the full-length proteins. Our in vitro findings provide evidence that FtsZ1 counterbalances the stability of FtsZ2 filaments in the regulation of chloroplast Z-ring dynamics and suggest that restraining FtsZ2 self-assembly is a critical function of FtsZ1 in chloroplasts.

What Does "Good" Community and Public Engagement Look Like? Developing Relationships With Community Members in Global Health Research.

Community and public engagement (CPE) is increasingly becoming a key component in global health research. The National Institute for Health Research (NIHR) is one of the leading funders in the UK of global health research and requires a robust CPE element in the research it funds, along with CPE monitoring and evaluation. But what does "good" CPE look like? And what factors facilitate or inhibit good CPE? Addressing these questions would help ensure clarity of expectations of award holders, and inform effective monitoring frameworks and the development of guidance. The work reported upon here builds on existing guidance and is a first step in trying to identify the key components of what "good" CPE looks like, which can be used for all approaches to global health research and in a range of different settings and contexts. This article draws on data collected as part of an evaluation of CPE by 53 NIHR-funded award holders to provide insights on CPE practice in global health research. This data was then debated, developed and refined by a group of researchers, CPE specialists and public contributors to explore what "good" CPE looks like, and the barriers and facilitators to good CPE. A key finding was the importance, for some research, of investing in and developing long term relationships with communities, perhaps beyond the life cycle of a project; this was regarded as crucial to the development of trust, addressing power differentials and ensuring the legacy of the research was of benefit to the community.

Allelic Variation in the Chloroplast Division Gene FtsZ2-2 Leads to Natural Variation in Chloroplast Size.

Chloroplast size varies considerably in nature, but the underlying mechanisms are unknown. By exploiting a near-isogenic line population derived from a cross between the Arabidopsis (Arabidopsis thaliana) accessions Cape Verde Islands (Cvi-1), which has larger chloroplasts, and Landsberg erecta (Ler-0), with smaller chloroplasts, we determined that the large-chloroplast phenotype in Cvi-1 is associated with allelic variation in the gene encoding the chloroplast-division protein FtsZ2-2, a tubulin-related cytoskeletal component of the contractile FtsZ ring inside chloroplasts. Sequencing revealed that the Cvi-1 FtsZ2-2 allele encodes a C-terminally truncated protein lacking a region required for FtsZ2-2 interaction with inner-envelope proteins, and functional complementation experiments in a Columbia-0 ftsZ2-2 null mutant confirmed this allele as causal for the increased chloroplast size in Cvi-1. Comparison of FtsZ2-2 coding sequences in the 1001 Genomes database showed that the Cvi-1 allele is rare and identified additional rare loss-of-function alleles, including a natural null allele, in three other accessions, all of which had enlarged-chloroplast phenotypes. The ratio of nonsynonymous to synonymous substitutions was higher among the FtsZ2-2 genes than among the two other FtsZ family members in Arabidopsis, FtsZ2-1, a close paralog of FtsZ2-2, and the functionally distinct FtsZ1-1, indicating more relaxed constraint on the FtsZ2-2 coding sequence than on those of FtsZ2-1 or FtsZ1-1 Our results establish that allelic variation in FtsZ2-2 contributes to natural variation in chloroplast size in Arabidopsis, and they also demonstrate that natural variation in Arabidopsis can be used to decipher the genetic basis of differences in fundamental cell biological traits, such as organelle size.

ARC3 Activation by PARC6 Promotes FtsZ-Ring Remodeling at the Chloroplast Division Site.

Chloroplast division is initiated by assembly of the stromal Z ring, composed of cytoskeletal Filamenting temperature-sensitive Z (FtsZ) proteins. Midplastid Z-ring positioning is governed by the chloroplast Min (Minicell) system, which inhibits Z-ring assembly everywhere except the division site. The central Min-system player is the FtsZ-assembly inhibitor ACCUMULATION AND REPLICATION OF CHLOROPLASTS3 (ARC3). Here, we report Arabidopsis (Arabidopsis thaliana) chloroplasts contain two pools of ARC3: one distributed throughout the stroma, which presumably fully inhibits Z-ring assembly at nondivision sites, and the other localized to a midplastid ring-like structure. We show that ARC3 is recruited to the middle of the plastid by the inner envelope membrane protein PARALOG OF ARC6 (PARC6). ARC3 bears a C-terminal Membrane Occupation and Recognition Nexus (MORN) domain; previous yeast two-hybrid experiments with full-length and MORN-truncated ARC3 showed the MORN domain mediates ARC3-PARC6 interaction but prevents ARC3-FtsZ interaction. Using yeast three-hybrid experiments, we demonstrate that the MORN-dependent ARC3-PARC6 interaction enables full-length ARC3 to bind FtsZ. The resulting PARC6/ARC3/FtsZ complex enhances the dynamics of Z rings reconstituted in a heterologous system. Our findings lead to a model whereby activation of midplastid-localized ARC3 by PARC6 facilitates Z-ring remodeling during chloroplast division by promoting Z-ring dynamics and reveal a novel function for MORN domains in regulating protein-protein interactions.

Interventions for preventing or treating malnutrition in homeless problem-drinkers: a systematic review.

BACKGROUND: Excessive drinking leads to poor absorption of nutrients and homeless problem-drinkers often have nutritionally inadequate diets. Depletion of nutrients such as vitamin B1 can lead to cognitive impairment, which can hinder efforts to reduce drinking or engage with services. This review aimed to assess effectiveness of interventions designed to prevent or treat malnutrition in homeless problem-drinkers. METHODS: We systematically searched nine electronic databases and 13 grey literature sources for studies evaluating interventions to improve nutrition in homeless populations, without regional or language restrictions. Screening for inclusion was done in duplicate. One reviewer extracted data and assessed risk of bias, and another checked the extractions. Primary outcomes were nutrition status/deficiency, liver damage, and cognitive function. Secondary outcomes included abstinence, comorbidities, resource use, acceptability and engagement with intervention. Results were synthesised narratively. RESULTS: We included 25 studies (2 Randomised Controlled Trials; 15 uncontrolled before and after; 7 surveys; 1 case-control). Nine studies evaluated educational and support interventions, five food provision, and three supplement provision. Eight studies evaluated a combination of these interventions. No two interventions were the same, and all studies were at high risk of bias. Nutritional status (intake/ deficiency) were reported in 11 studies and liver function in one. Fruit and vegetable intake improved with some education and support interventions (n = 4 studies) but not others (n = 2). Vitamin supplements appeared to improve vitamin deficiency levels in the blood (n = 2). Free or subsidised meals (n = 4) and food packs (n = 1) did not always fulfil dietary needs, but were usually considered acceptable by users. Some multicomponent interventions improved nutrition (n = 3) but acceptability varied (n = 3). No study reported cost effectiveness. CONCLUSIONS: The evidence for any one intervention for improving malnutrition in homeless problem-drinkers was based on single studies at high risk of bias. Various food and supplement provision interventions appear effective in changing nutritional status in single studies. Educational and multicomponent interventions show improved nutritional behaviour in some studies but not others. Further better quality evidence is required before these interventions can be recommended for implementation. Any future studies should seek the end user input in their design and conduct. TRIAL REGISTRATION: Registered with PROSPERO: CRD42015024247 .

Nutritional deficiencies in homeless persons with problematic drinking: a systematic review.

BACKGROUND: A significant proportion of homeless people drink alcohol excessively and this can lead to malnutrition and consequent medical problems. The aim of this review was to assess the evidence on the range of nutritional deficiencies in the homeless problem-drinking populations. METHODS: We conducted a comprehensive search of nine scientific literature databases and 13 grey literature sources. We included studies of any design that included homeless population with problem-drinking and reported measures of nutritional deficiencies in urine or blood. Study selection and data extraction was done by one reviewer and checked by another. Data on malnutrition profile were summarized narratively. RESULTS: We found nine studies reporting nutritional deficiencies in homeless populations with problem-drinking. The oldest study was from the 1950s and the most recent from 2013. The following nutrients were reported across studies: vitamins B1, B2, B6, B9, B12, C, A, and E; haemoglobin; and albumin. The most common deficiencies reported were of vitamin B1 (prevalence of deficiency was 0, 2, 6, 45, and 51% in five studies) and vitamin C (29, 84, and 95% in three studies). None of the studies were assessed to be at a low risk of bias. CONCLUSIONS: The limited, low quality and relatively old evidence suggests that homeless people who drink heavily may be deficient in vitamin C, thiamine, and other nutrients. New, well conducted studies are needed in order to optimally inform public health interventions aimed at improving deficiencies in this population. TRIAL REGISTRATION: PROSPERO CRD42015024247.

The Chloroplast Tubulin Homologs FtsZA and FtsZB from the Red Alga Galdieria sulphuraria Co-assemble into Dynamic Filaments.

FtsZ is a homolog of eukaryotic tubulin and is present in almost all bacteria and many archaea, where it is the major cytoskeletal protein in the Z ring, required for cell division. Unlike some other cell organelles of prokaryotic origin, chloroplasts have retained FtsZ as an essential component of the division machinery. However, chloroplast FtsZs have been challenging to study because they are difficult to express and purify. To this end, we have used a FATT tag expression system to produce as soluble proteins the two chloroplast FtsZs from Galdieria sulphuraria, a thermophilic red alga. GsFtsZA and GsFtsZB assembled individually in the presence of GTP, forming large bundles of protofilaments. GsFtsZA also assembled in the presence of GDP, the first member of the FtsZ/tubulin superfamily to do so. Mixtures of GsFtsZA and GsFtsZB assembled protofilament bundles and hydrolyzed GTP at a rate approximately equal to the sum of their individual rates, suggesting a random co-assembly. GsFtsZA assembly by itself in limiting GTP gave polymers that remained stable for a prolonged time. However, when GsFtsZB was added, the co-polymers disassembled with enhanced kinetics, suggesting that the GsFtsZB regulates and enhances disassembly dynamics. GsFtsZA-mts (where mts is a membrane-targeting amphipathic helix) formed Z ring-like helices when expressed in Escherichia coli Co-expression of GsFtsZB (without an mts) gave co-assembly of both into similar helices. In summary, we provide biochemical evidence that GsFtsZA assembles as the primary scaffold of the chloroplast Z ring and that GsFtsZB co-assembly enhances polymer disassembly and dynamics.

The Pseudomonas syringae Type III Effector HopG1 Induces Actin Remodeling to Promote Symptom Development and Susceptibility during Infection.

The plant cytoskeleton underpins the function of a multitude of cellular mechanisms, including those associated with developmental- and stress-associated signaling processes. In recent years, the actin cytoskeleton has been demonstrated to play a key role in plant immune signaling, including a recent demonstration that pathogens target actin filaments to block plant defense and immunity. Herein, we quantified spatial changes in host actin filament organization after infection with Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), demonstrating that the type-III effector HopG1 is required for pathogen-induced changes to actin filament architecture and host disease symptom development during infection. Using a suite of pathogen effector deletion constructs, coupled with high-resolution microscopy, we found that deletion of hopG1 from Pst DC3000 resulted in a reduction in actin bundling and a concomitant increase in the density of filament arrays in Arabidopsis, both of which correlate with host disease symptom development. As a mechanism underpinning this activity, we further show that the HopG1 effector interacts with an Arabidopsis mitochondrial-localized kinesin motor protein. Kinesin mutant plants show reduced disease symptoms after pathogen infection, which can be complemented by actin-modifying agents. In total, our results support a model in which HopG1 induces changes in the organization of the actin cytoskeleton as part of its virulence function in promoting disease symptom development.

From filaments to function: The role of the plant actin cytoskeleton in pathogen perception, signaling and immunity.

The eukaryotic actin cytoskeleton is required for numerous cellular processes, including cell shape, development and movement, gene expression and signal transduction, and response to biotic and abiotic stress. In recent years, research in both plants and animal systems have described a function for actin as the ideal surveillance platform, linking the function and activity of primary physiological processes to the immune system. In this review, we will highlight recent advances that have defined the regulation and breadth of function of the actin cytoskeleton as a network required for defense signaling following pathogen infection. Coupled with an overview of recent work demonstrating specific targeting of the plant actin cytoskeleton by a diversity of pathogens, including bacteria, fungi and viruses, we will highlight the importance of actin as a key signaling hub in plants, one that mediates surveillance of cellular homeostasis and the activation of specific signaling responses following pathogen perception. Based on the studies highlighted herein, we propose a working model that posits changes in actin filament organization is in and of itself a highly specific signal, which induces, regulates and physically directs stimulus-specific signaling processes, most importantly, those associated with response to pathogens.

Interventions for preventing or treating malnutrition in problem drinkers who are homeless or vulnerably housed: protocol for a systematic review.

BACKGROUND: Problem alcohol drinking in homeless and vulnerably housed people can lead to malnutrition, which is associated with complications such as alcohol-related brain damage. Homeless alcohol drinkers are likely to have worse health outcomes and different nutritional needs compared with housed alcohol-drinking persons. It is not clear whether interventions to improve nutritional status in this population have been effective. The purpose of this review is to assess the effectiveness and cost-effectiveness of interventions for preventing or correcting micronutrient deficiencies and other forms of malnutrition and related comorbidities in this population. METHODS/DESIGN: A systematic search for studies of a nutrition-based intervention applied in the homeless or vulnerably housed population with problem drinking will be conducted. The following electronic databases will be systematically searched for relevant studies: MEDLINE, EMBASE, Web of Science, PsycINFO, CAB abstracts, CINAHL, Cochrane Public Health Group Register and Cochrane Drugs and Alcohol Group Register. Screening of identified abstracts for relevance and assessment of papers for inclusion will be done in duplicate. One reviewer will extract data from the studies and assess quality, and this will be checked by another reviewer. Discrepancies will be resolved by consensus. The primary outcomes are (mal)nutrition status or micronutrient deficiencies or change in (mal)nutrition status or micronutrient deficiencies, measures of liver damage and cognitive function. Secondary outcomes include comorbidities, quality of life and functional scales, resources used to deliver treatment, uptake/acceptability of the intervention and engagement with treatment services. Results will be analysed descriptively, and, if appropriate, meta-analyses will be performed. DISCUSSION: The results of this review should help to inform the development of effective interventions that can be implemented in the community to improve the health of homeless people who are problem drinkers. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42015024247.

Actin branches out to link pathogen perception and host gene regulation.

Cellular functions of actin, and associated actin binding proteins (ABPs), have been well characterized with respect to their dynamic cytosolic role as components of the complex cytoskeletal network. In this regard, the collective research in this field has vastly expanded our knowledge of the role of actin to more recently identify a key role within the nucleus as an integral part gene organization and expression. Herein, we describe the requirement of the ABP actin depolymerizing factor-4 (ADF4) as a regulator of resistance to Pseudomonas syringae DC3000 expressing the effector AvrPphB via ADF4's cytosolic and nuclear functions. In total, our work has identified significant alterations in the expression of the resistance protein RPS5 in an ADF4 phosphorylation dependent manner. In this mini-review, we provide compelling evidence in support of both a nuclear function for ADF4, as well as potential targeting of the actin cytoskeleton by the bacterial effector AvrPphB.

Arabidopsis Actin-Depolymerizing Factor-4 links pathogen perception, defense activation and transcription to cytoskeletal dynamics.

The primary role of Actin-Depolymerizing Factors (ADFs) is to sever filamentous actin, generating pointed ends, which in turn are incorporated into newly formed filaments, thus supporting stochastic actin dynamics. Arabidopsis ADF4 was recently shown to be required for the activation of resistance in Arabidopsis following infection with the phytopathogenic bacterium Pseudomonas syringae pv. tomato DC3000 (Pst) expressing the effector protein AvrPphB. Herein, we demonstrate that the expression of RPS5, the cognate resistance protein of AvrPphB, was dramatically reduced in the adf4 mutant, suggesting a link between actin cytoskeletal dynamics and the transcriptional regulation of R-protein activation. By examining the PTI (PAMP Triggered Immunity) response in the adf4 mutant when challenged with Pst expressing AvrPphB, we observed a significant reduction in the expression of the PTI-specific target gene FRK1 (Flg22-Induced Receptor Kinase 1). These data are in agreement with recent observations demonstrating a requirement for RPS5 in PTI-signaling in the presence of AvrPphB. Furthermore, MAPK (Mitogen-Activated Protein Kinase)-signaling was significantly reduced in the adf4 mutant, while no such reduction was observed in the rps5-1 point mutation under similar conditions. Isoelectric focusing confirmed phosphorylation of ADF4 at serine-6, and additional in planta analyses of ADF4's role in immune signaling demonstrates that nuclear localization is phosphorylation independent, while localization to the actin cytoskeleton is linked to ADF4 phosphorylation. Taken together, these data suggest a novel role for ADF4 in controlling gene-for-gene resistance activation, as well as MAPK-signaling, via the coordinated regulation of actin cytoskeletal dynamics and R-gene transcription.

Molecular and biochemical basis for stress-induced accumulation of free and bound p-coumaraldehyde in cucumber.

To elucidate the genetic and biochemical regulation of elicitor-induced p-coumaraldehyde accumulation in plants, we undertook a multifaceted approach to characterize the metabolic flux through the phenylpropanoid pathway via the characterization and chemical analysis of the metabolites in the p-coumaryl, coniferyl, and sinapyl alcohol branches of this pathway. Here, we report the identification and characterization of four cinnamyl alcohol dehydrogenases (CADs) from cucumber (Cucumis sativus) with low activity toward p-coumaraldehyde yet exhibiting significant activity toward other phenylpropanoid hydroxycinnamaldehydes. As part of this analysis, we identified and characterized the activity of a hydroxycinnamoyl-coenzyme A:shikimate hydroxycinnamoyl transferase (HCT) capable of utilizing shikimate and p-coumaroyl-coenzyme A to generate p-coumaroyl shikimate. Following pectinase treatment of cucumber, we observed the rapid accumulation of p-coumaraldehyde, likely the result of low aldehyde reductase activity (i.e. alcohol dehydrogenase in the reverse reaction) of CsCAD enzymes on p-coumaraldehyde. In parallel, we noted a concomitant reduction in the activity of CsHCT. Taken together, our findings support the hypothesis that the up-regulation of the phenylpropanoid pathway upon abiotic stress greatly enhances the overall p-coumaryl alcohol branch of the pathway. The data presented here point to a role for CsHCT (as well as, presumably, p-coumarate 3-hydroxylase) as a control point in the regulation of the coniferyl and sinapyl alcohol branches of this pathway. This mechanism represents a potentially evolutionarily conserved process to efficiently and quickly respond to biotic and abiotic stresses in cucurbit plants, resulting in the rapid lignification of affected tissues.

Tissue- and isoform-specific phytochrome regulation of light-dependent anthocyanin accumulation in Arabidopsis thaliana.

Phytochromes regulate light- and sucrose-dependent anthocyanin synthesis and accumulation in many plants. Mesophyll-specific phyA alone has been linked to the regulation of anthocyanin accumulation in response to far-red light in Arabidopsis thaliana. However, multiple mesophyll-localized phytochromes were implicated in the photoregulation of anthocyanin accumulation in red-light conditions. Here, we report a role for mesophyll-specific phyA in blue-light-dependent regulation of anthocyanin levels and novel roles for individual phy isoforms in the regulation of anthocyanin accumulation under red illumination. These results provide new insight into spatial- and isoform-specific regulation of pigmentation by phytochromes in A. thaliana.

The pathogen-actin connection: a platform for defense signaling in plants.

The cytoskeleton, a dynamic network of cytoplasmic polymers, plays a central role in numerous fundamental processes, such as development, reproduction, and cellular responses to biotic and abiotic stimuli. As a platform for innate immune responses in mammalian cells, the actin cytoskeleton is a central component in the organization and activation of host defenses, including signaling and cellular repair. In plants, our understanding of the genetic and biochemical responses in both pathogen and host that are required for virulence and resistance has grown enormously. Additional advances in live-cell imaging of cytoskeletal dynamics have markedly altered our view of actin turnover in plants. In this review, we outline current knowledge of host resistance following pathogen perception, both in terms of the genetic interactions that mediate defense signaling, as well as the biochemical and cellular processes that are required for defense signaling.

Regulation of lipopolysaccharide-induced inflammatory response and endotoxemia by beta-arrestins.

Beta-arrestins are scaffolding proteins implicated as negative regulators of TLR4 signaling in macrophages and fibroblasts. Unexpectedly, we found that beta-arrestin-1 (beta-arr-1) and -2 knockout (KO) mice are protected from TLR4-mediated endotoxic shock and lethality. To identify the potential mechanisms involved, we examined the plasma levels of inflammatory cytokines/chemokines in the wild-type (WT) and beta-arr-1 and -2 KO mice after lipopolysaccharide (LPS, a TLR4 ligand) injection. Consistent with lethality, LPS-induced inflammatory cytokine levels in the plasma were markedly decreased in both beta-arr-1 and -2 KO, compared to WT mice. To further explore the cellular mechanisms, we obtained splenocytes (separated into CD11(b+) and CD11(b-) populations) from WT, beta-arr-1, and -2 KO mice and examined the effect of LPS on cytokine production. Similar to the in vivo observations, LPS-induced inflammatory cytokines were significantly blocked in both splenocyte populations from the beta-arr-2 KO compared to the WT mice. This effect in the beta-arr-1 KO mice, however, was restricted to the CD11(b-) splenocytes. Our studies further indicate that regulation of cytokine production by beta-arrestins is likely independent of MAPK and IkappaBalpha-NFkappaB pathways. Our results, however, suggest that LPS-induced chromatin modification is dependent on beta-arrestin levels and may be the underlying mechanistic basis for regulation of cytokine levels by beta-arrestins in vivo. Taken together, these results indicate that beta-arr-1 and -2 mediate LPS-induced cytokine secretion in a cell-type specific manner and that both beta-arrestins have overlapping but non-redundant roles in regulating inflammatory cytokine production and endotoxic shock in mice.

Physical limitations contribute to food insecurity and the food insecurity-obesity paradox in older adults at senior centers in Georgia.

The purpose of this study was to explore the relationship of obesity and physical limitations with food insecurity among Georgians participating in the Older Americans Act (OAA) congregate meal-site program (N = 621, median age = 76 years, 83% female, 36% Black, and 64% White, convenience sample). Food insecurity was assessed using the modified 6-item US Household Food Security Survey Module; obesity was defined as Body Mass Index (BMI) or waist circumference (WC) class I or II obesity; and physical limitations (arthritis, joint pain, poor physical function, weight-related disability) were based on the Disablement Process. A series of multivariate logistic regression models found weight-related disability and obesity (WC class II) may be potential risk factors for food insecurity. Thus, obesity and weight-related disability may be risk factors to consider when assessing the risk of food insecurity and the need for food assistance in this vulnerable subgroup of older adults.