Phenotypic diversity and altered environmental plasticity in Arabidopsis thaliana with reduced Hsp90 levels

The molecular chaperone HSP90 aids the maturation of a diverse but select set of metastable protein clients, many of which are key to a variety of signal transduction pathways. HSP90 function has been best investigated in animal and fungal systems, where inhibition of the chaperone has exceptionally diverse effects, ranging from reversing oncogenic transformation to preventing the acquisition of drug resistance. Inhibition of HSP90 in the model plant Arabidopsis thaliana uncovers novel morphologies dependent on normally cryptic genetic variation and increases stochastic variation inherent to developmental processes. The biochemical activity of HSP90 is strictly conserved between animals and plants. However, the substrates and pathways dependent on HSP90 in plants are poorly understood. Progress has been impeded by the necessity of reliance on light-sensitive HSP90 inhibitors due to redundancy in the A. thaliana HSP90 gene family. Here we present phenotypic and genome-wide expression analyses of A. thaliana with constitutively reduced HSP90 levels achieved by RNAi targeting. HSP90 reduction affects a variety of quantitative life-history traits, including flowering time and total seed set, increases morphological diversity, and decreases the developmental stability of repeated characters. Several morphologies are synergistically affected by HSP90 and growth temperature. Genome-wide expression analyses also suggest a central role for HSP90 in the genesis and maintenance of plastic responses. The expression results are substantiated by examination of the response of HSP90-reduced plants to attack by caterpillars of the generalist herbivore Trichoplusia ni. HSP90 reduction potentiates a more robust herbivore defense response. In sum, we propose that HSP90 exerts global effects on the environmental responsiveness of plants to many different stimuli. The comprehensive set of HSP90-reduced lines described here is a vital instrument to further examine the role of HSP90 as a central interface between organism, development, and environment.     

Two distinct mechanisms segregate Prospero in the longitudinal glia underlying the timing of interactions with axons

Prospero is required in dividing longitudinal glia (LG) during axon guidance; initially to enable glial division in response to neuronal contact, and subsequently to maintain glial precursors in a quiescent state with mitotic potential. Only Prospero-positive LG respond to neuronal ablation by over-proliferating, mimicking a glial-repair response. Prospero is distributed unequally through the progeny cells of the longitudinal glioblast lineage. Just before axon contact the concentration of Prospero is higher in two of the four progeny cells, and after axon guidance Prospero is present only in six out of ten progeny LG. Here we ask how Prospero is distributed unequally in these two distinct phases. We show that before neuronal contact, longitudinal glioblasts undergo invaginating divisions, perpendicular to the ectodermal layer. Miranda is required to segregate Prospero asymmetrically up to the four glial-progeny stage. After neuronal contact, Prospero is present in only the LG that activate Notch signalling in response to Serrate provided by commissural axons, and Numb is restricted to the glia that do not contain Prospero. As a result of this dual regulation of Prospero deployment, glia are coupled to the formation and maintenance of axonal trajectories.     

Identification and structural basis of binding to host lung glycogen by streptococcal virulence factors

The ability of pathogenic bacteria to recognize host glycans is often essential to their virulence. Here we report structure-function studies of previously uncharacterized glycogen-binding modules in the surface-anchored pullulanases from Streptococcus pneumoniae (SpuA) and Streptococcus pyogenes (PulA). Multivalent binding to glycogen leads to a strong interaction with alveolar type II cells in mouse lung tissue. X-ray crystal structures of the binding modules reveal a novel fusion of tandem modules into single, bivalent functional domains. In addition to indicating a structural basis for multivalent attachment, the structure of the SpuA modules in complex with carbohydrate provides insight into the molecular basis for glycogen specificity. This report provides the first evidence that intracellular lung glycogen may be a novel target of pathogenic streptococci and thus provides a rationale for the identification of the streptococcal alpha-glucan-metabolizing machinery as virulence factors.     

Inundation,Hydrodynamics and Vegetation Influence Carbon Dioxide Concentrations in Amazon Floodplain Lakes

Ecosystems - Extensive floodplains and numerous lakes in the Amazon basin are well suited to examine the role of floodable lands within the context of the sources and processing of carbon within...     

Protein complexes associated with β-catenin differentially influence the differentiation profile of neonatal and adult CD8+ T cells

The canonical Wnt signaling pathway is a master cell regulator involved in CD8⁺ T cell proliferation and differentiation. In human CD8⁺ T cells, this pathway induces differentiation into memory cells or a “stem cell memory like” population, which is preferentially present in cord blood. To better understand the role of canonical Wnt signals in neonatal or adult blood, we compared the proteins associated with β-catenin, in nonstimulated and Wnt3a-stimulated human neonatal and adult naive CD8⁺ T cells. Differentially recruited proteins established different complexes in adult and neonatal cells. In the former, β-catenin-associated proteins were linked to cell signaling and immunological functions, whereas those of neonates were linked to proliferation and metabolism. Wnt3a stimulation led to the recruitment and overexpression of Wnt11 in adult cells and Wnt5a in neonatal cells, suggesting a differential connexion with planar polarity and Wnt/Ca²⁺ noncanonical pathways, respectively. The chromatin immunoprecipitation polymerase chain reaction β-catenin was recruited to a higher level on the promoters of cell renewal genes in neonatal cells and of differentiation genes in those of adults. We found a preferential association of β-catenin with CBP in neonatal cells and with p300 in the adult samples, which could be involved in a higher self-renewal capacity of the neonatal cells and memory commitment in those of adults. Altogether, our results show that different proteins associated with β-catenin during Wnt3a activation mediate a differential response of neonatal and adult human CD8⁺ T cells.     

A field portable method for the semi‐quantitative estimation of dehydration tolerance of photosynthetic tissues across distantly related land plants

Desiccation tolerant (DT) plants withstand complete cellular dehydration, reaching relative water contents (RWC) below 30% in their photosynthetic tissues. Desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with differing degrees of DHT from truly DT plants. We developed a simple, feasible and portable protocol to differentiate between DT and different degrees of DHT in the photosynthetic tissues of seed plants and between fast desiccation (< 24 h) tolerant (FDT) and sensitive (FDS) bryophytes. The protocol is based on (1) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities that, consequently, induce three different speeds and extents of dehydration and (2) an evaluation of the average percentage of maximal photochemical efficiency of PSII (F_v/fm) recovery after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (1) imbibition of absorbent material with concentrated salt‐solutions inside the tubes provides stable relative humidity and avoids direct contact with samples; (2) for 50 ml capacity tubes, the optimal plant amount is 50–200 mg fresh weight; (3) the method is useful in remote locations due to minimal instrumental requirements; and (4) a threshold of 30% recovery of the initial F_v/fm upon reaching RWC ≤ 30% correctly categorises DT species, with three exceptions: two poikilochlorophyllous species and one gymnosperm. The protocol provides a semi‐quantitative expression of DHT that facilitates comparisons of species with different morpho‐physiological traits and/or ecological attributes.     

Effect of stirring speed on the production of phenolic secondary metabolites and growth of Buddleja cordata cells cultured in mechanically agitated bioreactor

Plant Cell, Tissue and Organ Culture (PCTOC) - Shake-flask in vitro culture of Buddleja cordata cells produces large amounts of biomass and synthetizes verbascoside (VB), linarin and...     

Improvement of almond production using Bombus terrestris (Hymenoptera: Apidae) in Mediterranean conditions

Almond trees are one of the most important crops in the Balearic Islands. The pollination of almonds is limited to the activity of insects, and cross‐pollination is necessary for fruit development. Currently, honey bees and wild bee populations are declining considerably due to multiple causes, such as the use of pesticides, diseases and habitat loss. An alternative to increase the almond production is the use of commercial pollinators. In this long‐term (3 years) study, the effect of the introduction of Bombus terrestris colonies on almond production was evaluated in two orchards. Two experimental designs were carried out to study the best management of this pollinator. For 2 years, all bumble bee colonies were placed in the middle of the plot and during the last year, the bumble bee colonies were distributed homogenously in the plot. Fruit set and the foraging behaviour of bumble bees during the blossoming period was determined, and the effect of different environmental variables on the visitation rate of bumble bees was assessed by means of a generalized linear mixed model (GLMM). Moreover, for the first time, the spatial distribution of fruit set was evaluated. Our results show that fruit set was significantly higher in the fields where B. terrestris had been introduced than in the control plots. This increased production resulted in a positive economic balance for the farmer. Moreover, bumble bees showed to prefer trees in a southwest orientation that were close to their colony. The activity of bumble bees showed to be significantly influenced by wind speed (the higher the speed the more flowers are visited by B. terrestris) and time after flowering (visitation rate decreased with days after flowering). In order to improve its management and obtain the highest possible almond production, it is important to understand the activity and behaviour of this pollinator.