Cloning of the Arabidopsis rwm1 gene for resistance to Watermelon mosaic virus points to a new function for natural virus resistance genes

Arabidopsis thaliana represents a valuable and efficient model to understand mechanisms underlying plant susceptibility to viral diseases. Here, we describe the identification and molecular cloning of a new gene responsible for recessive resistance to several isolates of Watermelon mosaic virus (WMV, genus Potyvirus) in the Arabidopsis Cvi‐0 accession. rwm1 acts at an early stage of infection by impairing viral accumulation in initially infected leaf tissues. Map‐based cloning delimited rwm1 on chromosome 1 in a 114‐kb region containing 30 annotated genes. Positional and functional candidate gene analysis suggested that rwm1 encodes cPGK2 (At1g56190), an evolutionary conserved nucleus‐encoded chloroplast phosphoglycerate kinase with a key role in cell metabolism. Comparative sequence analysis indicates that a single amino acid substitution (S78G) in the N‐terminal domain of cPGK2 is involved in rwm1‐mediated resistance. This mutation may have functional consequences because it targets a highly conserved residue, affects a putative phosphorylation site and occurs within a predicted nuclear localization signal. Transgenic complementation in Arabidopsis together with virus‐induced gene silencing in Nicotiana benthamiana confirmed that cPGK2 corresponds to rwm1 and that the protein is required for efficient WMV infection. This work uncovers new insight into natural plant resistance mechanisms that may provide interesting opportunities for the genetic control of plant virus diseases.     

Hessian fly Avirulence gene loss‐of‐function defeats plant resistance without compromising the larva's ability to induce a gall tissue

Plant pathogen effectors encoded by Avirulence (Avr) genes benefit the pathogen by promoting colonization and benefit plants that have a matching resistance (R) gene by constituting a signal that triggers resistance. The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), resembles a plant pathogen in showing R/Avr interactions. Because of these interactions, a wheat plant with the H13 resistance gene can be resistant or susceptible depending on the genotype of the larva that attacks the plant, being resistant if attack comes from a larva with a functional vH13 gene, but susceptible if attack comes from a larva with a non‐functional vH13 gene. In this study we asked: does this susceptible interaction involving plants with H13 look like susceptible interactions with plants lacking H13? Possibly, the H13 plant attacked by a larva with a non‐functional vH13 is induced to partial rather than complete resistance. Or the larva, lacking its vH13‐encoded effector, is compromised in its ability to induce susceptibility, which includes forcing the plant to create a gall nutritive tissue. Responses of epidermal cells to larval attack were explored using imaging techniques (light microscopy, scanning and transmission electron microscopy). Whole‐organism responses were investigated by measuring the growth of plants and larvae. No evidence was found for partial resistance responses by H13 plants or for a compromise in the ability of vH13 loss‐of‐function larvae to induce susceptibility. It appears that disrupting vH13 function is sufficient for overcoming the induced resistance mediated by the H13 gene.     

High local trait variability in a globally invasive cyanobacterium

相似文献   

Complete Genome Sequence of a Novel Wild tomato mosaic virus Isolate Infecting Nicotiana tabacum in China

Virus particles of approximately 740–760 nm in length and 13 nm in diameter were observed from a diseased Nicotiana tabacum (tobacco) plant in Sichuan Province, China. The complete genomic sequence of the virus isolate XC1 was determined to contain 9659 nucleotides without 3′ terminal poly(A) tail. XC1 has a genome typical of members of the genus Potyvirus, encoding a large polyprotein of 3075 amino acids. Putative proteolytic cleavage sites and a number of well characterized functional motifs were identified by sequence comparisons with those of known potyviruses. Sequence comparison revealed that XC1 shared the highest level of nucleotide sequence identity (76.5%) with Wild tomato mosaic virus (WTMV). Phylogenetic analysis showed that XC1 was closely related to the WTMV Guangdong isolate with an identity of 94.3% between CP gene sequence of the two viruses. We thus named XC1 WTMV‐XC‐1 as a novel isolate of WTMV. The full sequence of WTMV‐XC‐1 may serve as a basis for future investigations on the gene diversity of WTMV.     

Lotus japonicus SUNERGOS1 encodes a predicted subunit A of a DNA topoisomerase VI that is required for nodule differentiation and accommodation of rhizobial infection

A symbiotic mutant of Lotus japonicus, called sunergos1‐1 (suner1‐1), originated from a har1‐1 suppressor screen. suner1‐1 supports epidermal infection by Mesorhizobium loti and initiates cell divisions for organogenesis of nodule primordia. However, these processes appear to be temporarily stalled early during symbiotic interaction, leading to a low nodule number phenotype. This defect is ephemeral and near wild‐type nodule numbers are reached by suner1‐1 at a later point after infection. Using an approach that combined map‐based cloning and next‐generation sequencing we have identified the causative mutation and show that the suner1‐1 phenotype is determined by a weak recessive allele, with the corresponding wild‐type SUNER1 locus encoding a predicted subunit A of a DNA topoisomerase VI. Our data suggest that at least one function of SUNER1 during symbiosis is to participate in endoreduplication, which is an essential step during normal differentiation of functional, nitrogen‐fixing nodules.     

Arabidopsis DOK1 encodes a functional dolichol kinase involved in reproduction

Dolichol phosphate (Dol‐P) serves as a carrier of complex polysaccharides during protein glycosylation. Dol‐P is synthesized by the phosphorylation of dolichol or the monodephosphorylation of dolichol pyrophosphate (Dol‐PP); however, the enzymes that catalyze these reactions remain unidentified in Arabidopsis thaliana. We performed a genome‐wide search for cytidylyltransferase motif‐containing proteins in Arabidopsis, and found that At3g45040 encodes a protein homologous with Sec59p, a dolichol kinase (DOK) in Saccharomyces cerevisiae. At3g45040, designated AtDOK1, complemented defects in the growth and N‐linked glycosylation of the S. cerevisiae sec59 mutant, suggesting that AtDOK1 encodes a functional DOK. To characterize the physiological roles of AtDOK1 in planta, we isolated two independent lines of T‐DNA‐tagged AtDOK1 mutants, dok1‐1 and dok1‐2. The heterozygous plants showed developmental defects in male and female gametophytes, including an aberrant pollen structure, low pollen viability, and short siliques. Additionally, the mutations had incomplete penetrance. These results suggest that AtDOK1 is a functional DOK required for reproductive processes in Arabidopsis.     

Functionally Similar Species Confer Greater Resistance to Invasion: Implications for Grassland Restoration

Plant community functional composition can be manipulated in restored ecosystems to reduce the establishment potential of invading species. This study was designed to compare invasion resistance among communities with species functionally similar or dissimilar to yellow starthistle (Centaurea solstitialis), a late‐season annual. A field experiment was conducted in the Central Valley of California with six experimental plant communities that included (1) six early‐season native annual forbs (AF); (2) five late‐season native perennials and one summer annual forb (NP); (3) a combination of three early‐season native annual forbs and three late‐season native perennials (FP); (4) six early‐season non‐native annual grasses (AG); (5) monoculture of the late‐season native perennial grass Elymus glaucus (EG); and (6) monoculture of the late‐season native perennial Grindelia camporum (GC). Following establishment, C. solstitialis seed was added to half of the plots, and a monoculture of C. solstitialis (CS) was established as a control. Over a 5‐year period, the AF and AG communities were ineffective at preventing C. solstitialis invasion. Centaurea solstitialis cover remained less than 10% in the FP and NP communities, except in year 1. By the fourth year, E. glaucus cover was greater than 50% in NP and FP communities and had spread to all other communities (e.g., 27% cover in CS in year 5). Communities containing E. glaucus, which is functionally similar to C. solstitialis, better resisted invasion than communities lacking a functional analog. In contrast, G. camporum, which is also functionally similar to C. solstitialis, failed to survive. Consequently, species selection for restored communities must consider not only functional similarity to the invader but also establishment success, competitiveness, and survivorship.     

Species‐specific adaptations explain resilience of herbaceous understorey to increased precipitation variability in a Mediterranean oak woodland

To date, the implications of the predicted greater intra‐annual variability and extremes in precipitation on ecosystem functioning have received little attention. This study presents results on leaf‐level physiological responses of five species covering the functional groups grasses, forbs, and legumes in the understorey of a Mediterranean oak woodland, with increasing precipitation variability, without altering total annual precipitation inputs. Although extending the dry period between precipitation events from 3 to 6 weeks led to increased soil moisture deficit, overall treatment effects on photosynthetic performance were not observed in the studied species. This resilience to prolonged water stress was explained by different physiological and morphological strategies to withstand periods below the wilting point, that is, isohydric behavior in Agrostis, Rumex, and Tuberaria, leaf succulence in Rumex, and taproots in Tolpis. In addition, quick recovery upon irrigation events and species‐specific adaptations of water‐use efficiency with longer dry periods and larger precipitation events contributed to the observed resilience in productivity of the annual plant community. Although none of the species exhibited a change in cover with increasing precipitation variability, leaf physiology of the legume Ornithopus exhibited signs of sensitivity to moisture deficit, which may have implications for the agricultural practice of seeding legume‐rich mixtures in Mediterranean grassland‐type systems. This highlights the need for long‐term precipitation manipulation experiments to capture possible directional changes in species composition and seed bank development, which can subsequently affect ecosystem state and functioning.     

Identification of a novel population of highly cytotoxic c‐Met‐expressing CD8+ T lymphocytes

CD8⁺ cytotoxic T lymphocytes (CTLs) are critical mediators of anti‐tumor immunity, and controlling the mechanisms that govern CTL functions could be crucial for enhancing patient outcome. Previously, we reported that hepatocyte growth factor (HGF) limits effective murine CTL responses via antigen‐presenting cells. Here, we show that a fraction of murine effector CTLs expresses the HGF receptor c‐Met (c‐Met⁺ CTLs). Phenotypic and functional analysis of c‐Met⁺ CTLs reveals that they display enhanced cytolytic capacities compared to their c‐Met^? CTL counterparts. Furthermore, HGF directly restrains the cytolytic function of c‐Met⁺ CTLs in cell‐mediated cytotoxicity reactions in vitro and in vivo and abrogates T‐cell responses against metastatic melanoma in vivo. Finally, we establish in three murine tumor settings and in human melanoma tissues that c‐Met⁺ CTLs are a naturally occurring CD8⁺ T‐cell population. Together, our findings suggest that the HGF/c‐Met pathway could be exploited to control CD8⁺ T‐cell‐mediated anti‐tumor immunity.     

A single‐nucleotide polymorphism of miR‐146a and psoriasis: an association and functional study

Epidermal growth factor receptor (EGFR), which is overexpressed in psoriatic lesions, has been proven to contribute to the hyperproliferation of keratinocytes in psoriasis. Single nucleotide polymorphisms (SNPs) involved in miRNAs that can regulate the expression of EGFR could potentially influence the development of psoriasis. The present study investigated the association between a functional SNP of rs2910164 in miR‐146a and the risk of psoriasis in the Chinese Han population. A total of 521 Han Chinese patients with psoriasis and 582 healthy controls were recruited in this study. The miR‐146a rs2910164 SNP was genotyped by polymerase chain reaction‐restriction fragment length polymorphism. Overall, a significantly increased risk of psoriasis was associated with the rs2910164 miR‐146a CG and GG genotypes (adjusted OR, 1.38; 95% CI, 1.06–1.80). Furthermore, the rs2910164G allele in miR‐146a attenuated its inhibitory regulation on the expression of EGFR as well as the proliferation of human keratinocytes, and lowered the level of miR‐146a in the psoriatic lesions. These findings indicate that the rs2910164G allele in miR‐146a weakens its suppression on the proliferation of keratinocytes probably through the decreased inhibition of the target gene, EGFR, which may account for the increased risk of psoriasis in this study population.     

Why SNP rs227584 is associated with human BMD and fracture risk? A molecular and cellular study in bone cells

A large number of SNPs significant for osteoporosis (OP) had been identified by genome‐wide association studies. However, the underlying association mechanisms were largely unknown. From the perspective of protein phosphorylation, gene expression regulation, and bone cell activity, this study aims to illustrate association mechanisms for representative SNPs of interest. We utilized public databases and bioinformatics tool to identify OP‐associated SNPs which potentially influence protein phosphorylation (phosSNPs). Associations with hip/spine BMD, as well as fracture risk, in human populations for one significant phosSNP, that is, rs227584 (major/minor allele: C/A, EAS population) located in C17orf53 gene, were suggested in prior meta‐analyses. Specifically, carriers of allele C had significant higher BMD and lower risk of low‐trauma fractures than carriers of A. We pursued to test the molecular and cellular functions of rs227584 in bone through osteoblastic cell culture and multiple assays. We identified five phosSNPs significant for OP (P < 0.01). The osteoblastic cells, which was transfected with wild‐type C17orf53 (allele C at rs227584, P126), demonstrated specific interaction with NEK2 kinase, increased expression levels of osteoblastic genes significantly (OPN, OCN, COL1A1, P < 0.05), and promoted osteoblast growth and ALP activity, in contrast to those transfected with mutant C17orf53 (allele A at rs227584, T126). In the light of the consistent evidences between the present functional study in human bone cells and the prior association studies in human populations, we conclude that the SNP rs227584, via altering protein‐kinase interaction, regulates osteoblastic gene expression, influences osteoblast growth and activity, hence to affect BMD and fracture risk in humans.     

Mutagenesis of kiwifruit CENTRORADIALIS‐like genes transforms a climbing woody perennial with long juvenility and axillary flowering into a compact plant with rapid terminal flowering

Annualization of woody perennials has the potential to revolutionize the breeding and production of fruit crops and rapidly improve horticultural species. Kiwifruit (Actinidia chinensis) is a recently domesticated fruit crop with a short history of breeding and tremendous potential for improvement. Previously, multiple kiwifruit CENTRORADIALIS (CEN)‐like genes have been identified as potential repressors of flowering. In this study, CRISPR/Cas9‐ mediated manipulation enabled functional analysis of kiwifruit CEN‐like genes AcCEN4 and AcCEN. Mutation of these genes transformed a climbing woody perennial, which develops axillary inflorescences after many years of juvenility, into a compact plant with rapid terminal flower and fruit development. The number of affected genes and alleles and severity of detected mutations correlated with the precocity and change in plant stature, suggesting that a bi‐allelic mutation of either AcCEN4 or AcCEN may be sufficient for early flowering, whereas mutations affecting both genes further contributed to precocity and enhanced the compact growth habit. CRISPR/Cas9‐mediated mutagenesis of AcCEN4 and AcCEN may be a valuable means to engineer Actinidia amenable for accelerated breeding, indoor farming and cultivation as an annual crop.     

Morphological convergence in a Mexican garter snake associated with the ingestion of a novel prey

Morphological convergence is expected when organisms which differ in phenotype experience similar functional demands, which lead to similar associations between resource utilization and performance. To consume prey with hard exoskeletons, snakes require either specialized head morphology, or to deal with them when they are vulnerable, for example, during molting. Such attributes may in turn reduce the efficiency with which they prey on soft‐bodied, slippery animals such as fish. Snakes which consume a range of prey may present intermediate morphology, such as that of Thamnophiine (Natricinae), which may be classified morphometrically across the soft–hard prey dietary boundary. In this study, we compared the dentition and head structure of populations of Thamnophis melanogaster that have entered the arthropod–crustacean (crayfish)‐eating niche and those that have not, and tested for convergence between the former and two distantly related crayfish specialists of the genus Regina (R. septemvittata and R. grahamii). As a control, we included the congener T. eques. Multivariate analysis of jaw length, head length, head width, and number of maxillary teeth yielded three significant canonical variables that together explained 98.8% of the variance in the size‐corrected morphological data. The first canonical variable significantly discriminated between the three species. The results show that head dimensions and number of teeth of the two Regina species are more similar to those of crayfish‐eating T. melanogaster than to non‐crayfish‐eating snakes or of T. eques. It is unclear how particular head proportions or teeth number facilitates capture of crayfish, but our results and the rarity of soft crayfish ingestion by T. melanogaster may reflect the novelty of this niche expansion, and are consistent with the hypothesis that some populations of T. melanogaster have converged in their head morphology with the two soft crayfish‐eating Regina species, although we cannot rule out the possibility of a morphological pre‐adaptation to ingest crayfish.     

Near‐genomewide RNAi screening for regulators of BRAFV600E‐induced senescence identifies RASEF,a gene epigenetically silenced in melanoma

The activation of oncogenes in primary cells blocks proliferation by inducing oncogene‐induced senescence (OIS), a highly potent in vivo tumor‐suppressing program. A prime example is mutant BRAF, which drives OIS in melanocytic nevi. Progression to melanoma occurs only in the context of additional alteration(s) like the suppression of PTEN, which abrogates OIS. Here, we performed a near‐genomewide short hairpin (sh)RNA screen for novel OIS regulators and identified by next generation sequencing and functional validation seven genes. While all but one were upregulated in OIS, depletion of each of them abrogated BRAF^V600E‐induced arrest. With genome‐wide DNA methylation analysis, we found one of these genes, RASEF, to be hypermethylated in primary cutaneous melanomas but not nevi. Bypass of OIS by depletion of RASEF was associated with suppression of several senescence biomarkers including senescence‐associated (SA)‐β‐galactosidase activity, interleukins, and tumor suppressor p15^INK4B. Restoration of RASEF expression inhibited proliferation. These results illustrate the power of shRNA OIS bypass screens and identify a potential novel melanoma suppressor gene.     

‘Real time’ genetic manipulation: a new tool for ecological field studies

Field experiments with transgenic plants often reveal the functional significance of genetic traits that are important for the performance of the plants in their natural environments. Until now, only constitutive overexpression, ectopic expression and gene silencing methods have been used to analyze gene‐related phenotypes in natural habitats. These methods do not allow sufficient control over gene expression for the study of ecological interactions in real time, of genetic traits that play essential roles in development, or of dose‐dependent effects. We applied the sensitive dexamethasone (DEX)‐inducible pOp6/LhGR expression system to the ecological model plant Nicotiana attenuata and established a lanolin‐based DEX application method to facilitate ectopic gene expression and RNA interference‐mediated gene silencing in the field and under challenging conditions (e.g. high temperature, wind and UV radiation). Fully established field‐grown plants were used to silence phytoene desaturase and thereby cause photobleaching only in specific plant sectors, and to activate expression of the cytokinin (CK) biosynthesis gene isopentenyl transferase (ipt). We used ipt expression to analyze the role of CKs in both the glasshouse and the field to understand resistance to the native herbivore Tupiocoris notatus, which attacks plants at small spatial scales. By spatially restricting ipt expression and elevating CK levels in single leaves, damage by T. notatus increased, demonstrating the role of CKs in this plant–herbivore interaction at a small scale. As the arena of most ecological interactions is highly constrained in time and space, these tools will advance the genetic analysis of dynamic traits that matter for plant performance in nature.