Simple, but Not Branched, Plasmodesmata Allow the Nonspecific Trafficking of Proteins in Developing Tobacco Leaves

AbstractLeaves undergo a sink–source transition during which a physiological change occurs from carbon import to export. In sink leaves, biolistic bombardment of plasmids encoding GFP-fusion proteins demonstrated that proteins with an Mr up to 50 kDa could move freely through plasmodesmata. During the sink–source transition, the capacity to traffic proteins decreased substantially and was accompanied by a developmental switch from simple to branched forms of plasmodesmata. Inoculation of sink leaves with a movement protein-defective virus showed that virally expressed GFP, but not viral RNA, was capable of trafficking between sink cells during infection. Contrary to dogma that plasmodesmata have a size exclusion limit below 1 kDa, the data demonstrate that nonspecific “macromolecular trafficking” is a general feature of simple plasmodesmata in sink leaves

Phloem connectivity and transport are not involved in mature plant resistance (MPR) to Potato Virus Y in different potato cultivars, and MPR does not protect tubers from recombinant strains of the virus

This research was funded by UK Research and Innovation (BBSRC Grant # BB/L011840/1; Ecology and Epidemiology of Infectious Diseases), by the Scottish Government's Rural and Environment Science and Analytical Services (RESAS) Division, and by the James Hutton Institute.The aims of this study were: i) to investigate mature plant resistance (MPR) against four strains of Potato virus Y (PVYO, PVYN, PVYNTN and PVYN−Wi) in potato cultivars that differ in maturity (e.g. early or maincrop) at different developmental stages, and ii) to determine whether phloem translocation of photoassimilates at different stages including the source-sink transition influences MPR. The data showed that MPR was functional by the flowering stage in all cultivars, and that the host-pathogen interaction is highly complex, with all three variables (potato cultivar, virus strain and developmental stage of infection) having a significant effect on the outcome. However, virus strain was the most important factor, and MPR was less effective in protecting tubers from recombinant virus strains (PVYNTN and PVYN−Wi). Development of MPR was unrelated to foliar phloem connectivity, which was observed at all developmental stages, but a switch from symplastic to apoplastic phloem unloading early in tuber development may be involved in the prevention of tuber infections with PVYO. Recombinant virus strains were more infectious than parental strains and PVYNTN has a more effective silencing suppressor than PVYO, another factor that may contribute to the efficiency of MPR. The resistance conferred by MPR against PVYO or PVYN may be associated with or enhanced by the presence of the corresponding strain-specific HR resistance gene in the cultivar.Publisher PDFPeer reviewe

Cellulose synthase ‘class specific regions’ are intrinsically disordered and functionally undifferentiated

Cellulose synthases (CESAs) are glycosyltransferases that catalyze formation of cellulose microfibrils in plant cell walls. Seed plant CESA isoforms cluster in six phylogenetic clades, whose non‐interchangeable members play distinct roles within cellulose synthesis complexes (CSCs). A ‘class specific region’ (CSR), with higher sequence similarity within versus between functional CESA classes, has been suggested to contribute to specific activities or interactions of different isoforms. We investigated CESA isoform specificity in the moss, Physcomitrella patens (Hedw.) B. S. G. to gain evolutionary insights into CESA structure/function relationships. Like seed plants, P. patens has oligomeric rosette‐type CSCs, but the PpCESAs diverged independently and form a separate CESA clade. We showed that P. patens has two functionally distinct CESAs classes, based on the ability to complement the gametophore‐negative phenotype of a ppcesa5 knockout line. Thus, non‐interchangeable CESA classes evolved separately in mosses and seed plants. However, testing of chimeric moss CESA genes for complementation demonstrated that functional class‐specificity is not determined by the CSR. Sequence analysis and computational modeling showed that the CSR is intrinsically disordered and contains predicted molecular recognition features, consistent with a possible role in CESA oligomerization and explaining the evolution of class‐specific sequences without selection for class‐specific function

Achievement goals, self-handicapping, and performance: A 2 × 2 achievement goal perspective

Elliot and colleagues (2006) examined the effects of experimentally induced achievement goals, proposed by the trichotomous model, on self-handicapping and performance in physical education. Our study replicated and extended the work of Elliot et al. by experimentally promoting all four goals proposed by the 262 model (Elliot & McGregor, 2001), measuring the participants’ own situational achievement goals, using a relatively novel task, and testing the participants in a group setting. We used a randomized experimental design with four conditions that aimed to induce one of the four goals advanced by the 262 model. The participants (n¼138) were undergraduates who engaged in a dart-throwing task. The results pertaining to self-handicapping partly replicated Elliot and colleagues’ findings by showing that experimentally promoted performance-avoidance goals resulted in less practice. In contrast, the promotion of mastery-avoidance goals did not result in less practice compared with either of the approach goals. Dart-throwing performance did not differ among the four goal conditions. Personal achievement goals did not moderate the effects of experimentally induced goals on selfhandicapping and performance. The extent to which mastery-avoidance goals are maladaptive is discussed, as well as the interplay between personal and experimentally induced goals

How parents and children evaluate emollients for childhood eczema: a qualitative study

BACKGROUND: Eczema affects one in five children in the UK. Regular application of emollients is routinely recommended for children with eczema. There are four main emollient types, but no clear evidence of which is best. The current ‘trial and error’ approach to find suitable emollients can be frustrating for parents, children, and clinicians. AIM: To identify how parents and children experience and evaluate emollients. DESIGN AND SETTING: Qualitative interview study, nested within a primary care trial of emollients (Best Emollients for Eczema [BEE] trial). METHOD: Semi-structured interviews with children with eczema and their parents were conducted. Participants were purposively sampled on emollient type (lotion, cream, gel, or ointment), age, and eczema severity. RESULTS: Forty-four parents were interviewed, with children participating in 24 of those interviews. There was no clear preference for any one emollient type. The strongest theme was the variation of experience in each of the four types. Participants focused on thickness and absorbency, both positively and negatively, to frame their evaluations. Effectiveness and acceptability were both considered when evaluating an emollient but effectiveness was the primary driver for continued use. For some, participating in the trial had changed their knowledge and behaviour of emollients, resulting in use that was more regular and for a longer duration. CONCLUSION: There is no one emollient that is suitable for everyone, and parents/children prioritise different aspects of emollients. Future research could evaluate decision aids and/or tester pots of different types, which could enable clinicians and parents/children to work collaboratively to identify the best emollient for them

Potato mop-top virus co-opts the stress sensor HIPP26 for long-distance movement

The work of LT, GC, SJ and AR is funded by the Scottish Government’s Rural and Environmental Science and Analytical Services (RESAS) Division, PH by the BBSRC (grant BB/M024911/1) and The Royal Society and EIS by the Swedish Research Council Formas and the Carl Tryggers Foundation.Virus movement proteins facilitate virus entry into the vascular system to initiate systemic infection. The potato mop-top virus (PMTV) movement protein, TGB1, is involved in long-distance movement of both viral ribonucleoprotein complexes and virions. Here, our analysis of TGB1 interactions with host Nicotiana benthamiana proteins revealed an interaction with a member of the heavy metal-associated isoprenylated plant protein family, HIPP26, which acts as a plasma membrane-to-nucleus signal during abiotic stress. We found that knockdown of NbHIPP26 expression inhibited virus long-distance movement but did not affect cell-to-cell movement. Drought and PMTV infection up-regulated NbHIPP26 gene expression, and PMTV infection protected plants from drought. In addition, NbHIPP26 promoter-reporter fusions revealed vascular tissue-specific expression. Mutational and biochemical analyses indicated that NbHIPP26 subcellular localization at the plasma membrane and plasmodesmata was mediated by lipidation (S-acylation and prenylation), as nonlipidated NbHIPP26 was predominantly in the nucleus. Notably, coexpression of NbHIPP26 with TGB1 resulted in a similar nuclear accumulation of NbHIPP26. TGB1 interacted with the carboxyl-terminal CVVM (prenyl) domain of NbHIPP26, and bimolecular fluorescence complementation revealed that the TGB1-HIPP26 complex localized to microtubules and accumulated in the nucleolus, with little signal at the plasma membrane or plasmodesmata. These data support a mechanism where interaction with TGB1 negates or reverses NbHIPP26 lipidation, thus releasing membrane-associated NbHIPP26 and redirecting it via microtubules to the nucleus, thereby activating the drought stress response and facilitating virus long-distance movement.PostprintPeer reviewe

Comparative Structural and Computational Analysis Supports Eighteen Cellulose Synthases in the Plant Cellulose Synthesis Complex

A six-lobed membrane spanning cellulose synthesis complex (CSC) containing multiple cellulose synthase (CESA) glycosyltransferases mediates cellulose microfibril formation. The number of CESAs in the CSC has been debated for decades in light of changing estimates of the diameter of the smallest microfibril formed from the β-1,4 glucan chains synthesized by one CSC. We obtained more direct evidence through generating improved transmission electron microscopy (TEM) images and image averages of the rosette-type CSC, revealing the frequent triangularity and average cross-sectional area in the plasma membrane of its individual lobes. Trimeric oligomers of two alternative CESA computational models corresponded well with individual lobe geometry. A six-fold assembly of the trimeric computational oligomer had the lowest potential energy per monomer and was consistent with rosette CSC morphology. Negative stain TEM and image averaging showed the triangularity of a recombinant CESA cytosolic domain, consistent with previous modeling of its trimeric nature from small angle scattering (SAXS) data. Six trimeric SAXS models nearly filled the space below an average FF-TEM image of the rosette CSC. In summary, the multifaceted data support a rosette CSC with 18 CESAs that mediates the synthesis of a fundamental microfibril composed of 18 glucan chains

Parents and GPs’ understandings and beliefs about food allergy testing in children with eczema:qualitative interview study within the Trial of Eczema allergy Screening Tests (TEST) feasibility trial

Aim To explore parent and general practitioner (GP) understanding and beliefs about food allergy testing for children with eczema.Design and setting Qualitative interview study in UK primary care within the Trial of Eczema allergy Screening Tests feasibility trial.Participants Semi-structured interviews with parents of children with eczema taking part in the feasibility study and GPs at practices hosting the study.Results 21 parents and 11 GPs were interviewed. Parents discussed a range of potential causes for eczema, including a role for food allergy. They believed allergy testing to be beneficial as it could potentially identify a cure or help reduce symptoms and they found negative tests reassuring, suggesting to them that no dietary changes were needed. GPs reported limited experience and uncertainty regarding food allergy in children with eczema. While some GPs believed referral for allergy testing could be appropriate, most were unclear about its utility. They thought it should be reserved for children with severe eczema or complex problems but wanted more information to advise parents and help guide decision making.Conclusions Parents’ motivations for allergy testing are driven by the desire to improve their child’s condition and exclude food allergy as a possible cause of symptoms. GPs are uncertain about the role of allergy testing and want more information about its usefulness to support parents and help inform decision making.Trial registration number ISRCTN15397185