The influence of experimentally induced polyploidy on the relationships between endopolyploidy and plant function in Arabidopsis thaliana

Whole genome duplication, leading to polyploidy and endopolyploidy, occurs in all domains and kingdoms and is especially prevalent in vascular plants. Both polyploidy and endopolyploidy increase cell size, but it is unclear whether both processes have similar effects on plant morphology and function, or whether polyploidy influences the magnitude of endopolyploidy. To address these gaps in knowledge, fifty‐five geographically separated diploid accessions of Arabidopsis thaliana that span a gradient of endopolyploidy were experimentally manipulated to induce polyploidy. Both the diploids and artificially induced tetraploids were grown in a common greenhouse environment and evaluated with respect to nine reproductive and vegetative characteristics. Induced polyploidy decreased leaf endopolyploidy and stem endopolyploidy along with specific leaf area and stem height, but increased days to bolting, leaf size, leaf dry mass, and leaf water content. Phenotypic responses to induced polyploidy varied significantly among accessions but this did not affect the relationship between phenotypic traits and endopolyploidy. Our results provide experimental support for a trade‐off between induced polyploidy and endopolyploidy, which caused induced polyploids to have lower endopolyploidy than diploids. Though polyploidy did not influence the relationship between endopolyploidy and plant traits, phenotypic responses to experimental genome duplication could not be easily predicted because of strong cytotype by accession interactions.     

Spatial patterns of plant diversity below-ground as revealed by DNA barcoding

Our understanding of the spatial organization of root diversity in plant communities and of the mechanisms of community assembly has been limited by our ability to identify plants based on root tissue, especially in diverse communities. Here, we test the effectiveness of the plastid gene rbcL, a core plant DNA barcoding marker, for investigating spatial patterns of root diversity, and relate observed patterns to above-ground community structure. We collected 3800 root fragments from four randomly positioned, 1-m-deep soil profiles (two vertical transects per plot), located in an old-field community in southern Ontario, Canada, and extracted and sequenced DNA from 1531 subsampled fragments. We identified species by comparing sequences with a DNA barcode reference library developed previously for the local flora. Nearly 85% of sampled root fragments were successfully sequenced and identified as belonging to 29 plant species or species groups. Root abundance and species richness varied in horizontal space and were negatively correlated with soil depth. The relative abundance of taxa below-ground was correlated with their frequency above-ground (r = 0.73, P = 0.0001), but several species detected in root tissue were not observed in above-ground quadrats. Multivariate analyses indicated that diversity was highly structured below-ground, and associated with depth, root morphology, soil chemistry and soil texture, whereas little structure was evident above-ground. Furthermore, analyses of species co-occurrence indicates strong species segregation overall but random co-occurrence among confamilials. Our results provide insights into the role of environmental filtering and competitive interactions in the organization of plant diversity below-ground, and also demonstrate the utility of barcoding for the identification of plant roots.     

Unusual growth pattern in the Frasnian alveolitids (Tabulata) from the Holy Cross Mountains (Poland)

Abstract: Growth periodicity is a phenomenon occurring in fossil and modern corals. The most apparent feature is growth banding, and environmental changes are broadly accepted as controls on this phenomenon. If environment controls the growth, then all corallites within a colony should repeat the same growth pattern, as individuals are clones and must have shared the same environment. A study on several species of Alveolitidae (Anthozoa, Tabulata) from the Late Devonian (Early Frasnian) of the Holy Cross Mountains (Poland) shows that the growth pattern varies between neighbouring individuals within the same corallum. This contradicts observations of closely related Favositida as demonstrated on Pachyfavosites sp. from the Givetian of Avesnois, France, where neighbouring individuals repeat the same pattern. Therefore, environmental control on growth rhythm in Alveolitidae can be excluded; the causes of differences between individuals remain unknown.     

Effects of a belowground mutualism on an aboveground mutualism

Studies of multitrophic interactions between below‐ and aboveground communities have generally focused on soil organisms and antagonists of plant shoots and leaves (herbivores). Despite the widespread occurrence of plant mutualists below‐ and aboveground which can occur on the same host plant, the potential for interactions between them has not been considered. Here we demonstrate that aboveground plant mutualists, insect pollinators, are strongly influenced by belowground plant mutualists, arbuscular mycorrhizal fungi. The presence of arbuscular mycorrhizal fungi in the roots of Chamerion angustifolium increased pollinator visitation and per cent seed set of this plant in the field by up to two times compared with non‐mycorrhizal plants. We propose that interactions between belowground and aboveground mutualisms are widespread and may play important functional roles in populations and communities.     

THE EFFECT OF INBREEDING IN DIPLOID AND TETRAPLOID POPULATIONS OF EPILOBIUM ANGUSTIFOLIUM (ONAGRACEAE): IMPLICATIONS FOR THE GENETIC BASIS OF INBREEDING DEPRESSION

The partial dominance model for the evolution of inbreeding depression predicts that tetraploids should exhibit less inbreeding depression than their diploid progenitors. We tested this prediction by comparing the magnitude of inbreeding depression in tetraploid and diploid populations of the herbaceous perennial Epilobium angustifolium (Onagraceae). Inbreeding depression was estimated in the greenhouse for three tetraploid and two diploid populations at four life stages. The mating system of a tetraploid population was estimated and compared to a previous estimate for diploids. Tetraploids showed less inbreeding depression than diploids at all life history stages, and these differences were significant for seed-set and cumulative fitness, but not for germination, survival, or plant dry mass at nine weeks. This result suggests that the genetic basis of inbreeding depression may differ among life stages. The primary selfing rate of the tetraploid population was r = 0.43, which is nearly identical to that of a diploid population (r = 0.45), indicating that differences in inbreeding depression between diploids and tetraploids are probably not due to differences in the mating system. Cumulative inbreeding depression, calculated from the four life history stages, was significantly higher for diploids () than for tetraploids (), supporting the partial dominance model of inbreeding depression.     

An association between the acute phase response and patterns of antigen induced T cell proliferation in juvenile idiopathic arthritis

The aim of this research was to determine whether all memory T cells have the same propensity to migrate to the joint in patients with juvenile idiopathic arthritis. Paired synovial fluid and peripheral blood mononuclear cell proliferative responses to a panel of antigens were measured and the results correlated with a detailed set of laboratory and clinical data from 39 patients with juvenile idiopathic arthritis. Two distinct patterns of proliferative response were found in the majority of patients: a diverse pattern, in which synovial fluid responses were greater than peripheral blood responses for all antigens tested; and a restricted pattern, in which peripheral blood responses to some antigens were more vigorous than those in the synovial fluid compartment. The diverse pattern was generally found in patients with a high acute phase response, whereas patients without elevated acute phase proteins were more likely to demonstrate a restricted pattern. We propose that an association between the synovial fluid T cell repertoire and the acute phase response suggests that proinflammatory cytokines may influence recruitment of memory T cells to an inflammatory site, independent of their antigen specificity. Additionally, increased responses to enteric bacteria and the presence of αEβ7 T cells in synovial fluid may reflect accumulation of gut associated T cells in the synovial compartment, even in the absence of an elevated acute phase response. This is the first report of an association between the acute phase response and the T cell population recruited to an inflammatory site.     

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Multiple origins of self-fertilization in tristylous Eichhornia paniculata (Pontederiaceae): Inferences from style morph and isozyme variation

Populations of Eichhornia paniculata (Pontederiaceae) exhibit a wide range of mating systems, from predominant outcrossing to high levels of self-fertilization. The origin of self-fertilization in this tristylous species is associated with the loss of style-length morphs from populations and the spread of self-pollinating, floral variants. We examined geographic variation in style morph and allozyme frequencies to determine whether the loss of style morphs and transition to selfing could have multiple origins in E. paniculata. Surveys of floral variation in 167 populations from six states in northeastern Brazil revealed that at least one style morph was absent from 29.3%. Non-trimorphic populations occurred in all states and ranged in frequency from 9% in Ceará to 68% in Alagoas. Selfing variants occurred in 8.5% and 55% of trimorphic and non-trimorphic populations, respectively, and were distributed among five of six states with primary concentrations in Alagoas and Pernambuco. A comparison of electrophoretic variation at 24 isozyme loci in 28 trimorphic, 13 dimorphic and 3 monomorphic populations indicated that non-trimorphic populations contained 84% of the allelic variation present in trimorphic populations and were markedly differentiated from one another. Analyses of genetic distance and the distribution of rare alleles indicated that non-trimorphic populations were often more similar to neighbouring trimorphic populations than to one another. Populations with selfing variants occurred at low frequency in three genetically distinct parts of the range. These results, in combination with genetic and morphological evidence suggest that style morphs are lost repeatedly from populations of E. paniculata and that selfing variants may have originated on at least three separate occasions in northeastern Brazil.