TWISTED DWARF1 regulates Arabidopsis stamen development by differential activation of ABCB-mediated auxin transport

Despite clear evidence that a local accumulation of auxin is likewise critical for male fertility, much less is known about the components that regulate auxin-controlled stamen development.In this study, we analyzed physiological and morphological parameters in mutants of key players of ABCB-mediated auxin transport and spatially and temporally dissected their expression on the protein level as well as auxin fluxes in the Arabidopsis stamens. Our analyses revealed that the FKBP42, TWISTED DWARF1 (TWD1), promotes stamen elongation and, to a lesser extent, anther dehiscence, as well as pollen maturation and thus is required for seed development. Most of the described developmental defects in twd1 are shared with the abcb1 abcb19 mutant, which can be attributed to the fact that TWD1 - as a described ABCB chaperon - is a positive regulator of ABCB1 and ABCB19-mediated auxin transport. However, reduced stamen number was dependent on TWD1 but not on investigated ABCBs, suggesting additional actors down-stream of TWD1. We predict an overall housekeeping function for ABCB1 during earlier stages, while ABCB19 seems to be responsible for the key event of rapid elongation at later stages of stamen development. Our data indicate that TWD1 controls stamen development by differential activation of ABCB-mediated auxin transport in the stamen.HighlightBy using a mix of phenotypical and imaging analyses, we here identify and functionally characterize a new master regulator of flower development.

Use of an Organic Fertilizer Also Having a Biostimulant Action to Promote the Growth of Young Olive Trees

In 2019–2020, trials were carried out with the aim of evaluating the possibilities of using an organic fertilizer, reported to have a biostimulant action, for promoting the growth of young olive trees. The experiments were implemented using both potted and field-grown trees. The effects of the organic fertilizer were evaluated with respect to trees treated with a chemical fertilizer; for potted trees a control without any fertilization was also used. Therefore, the compared treatments were: organic fertilization vs. chemical fertilization or no fertilization in the experiment with potted trees; organic fertilization vs. chemical fertilization in the experiment with field-grown trees. Non-fertilized potted trees had the lowest growth. The organic fertilizer, with respect to the chemical one, determined higher growth in both potted and field-grown trees (+22–29% of the increment of the trunk cross sectional area). In potted trees, it determined a rapid elongation of the stem (+30% of the increment of tree height with respect to chemically fertilized trees) and this likely favored the development of a higher number of leaves, which, together with an increase in their photosynthetic activity (in August, +27% with respect to chemical fertilized trees), created conditions for higher assimilate production and in turn greater tree growth. Trees in the field showed that the greater growth was not obtained at the expenses of reproductive growth, which increased to the same degree as the vegetative growth. Overall, the results support the biostimulant action of the organic fertilizer and indicate the possibility of its use to improve the growth of young olive trees.

Multiple morphogens and rapid elongation promote segmental patterning during development

The vertebrate hindbrain is segmented into rhombomeres (r) initially defined by distinct domains of gene expression. Previous studies have shown that noise-induced gene regulation and cell sorting are critical for the sharpening of rhombomere boundaries, which start out rough in the forming neural plate (NP) and sharpen over time. However, the mechanisms controlling simultaneous formation of multiple rhombomeres and accuracy in their sizes are unclear. We have developed a stochastic multiscale cell-based model that explicitly incorporates dynamic morphogenetic changes (i.e. convergent-extension of the NP), multiple morphogens, and gene regulatory networks to investigate the formation of rhombomeres and their corresponding boundaries in the zebrafish hindbrain. During pattern initiation, the short-range signal, fibroblast growth factor (FGF), works together with the longer-range morphogen, retinoic acid (RA), to specify all of these boundaries and maintain accurately sized segments with sharp boundaries. At later stages of patterning, we show a nonlinear change in the shape of rhombomeres with rapid left-right narrowing of the NP followed by slower dynamics. Rapid initial convergence improves boundary sharpness and segment size by regulating cell sorting and cell fate both independently and coordinately. Overall, multiple morphogens and tissue dynamics synergize to regulate the sizes and boundaries of multiple segments during development.

Cynodon plectostachyus (African stargrass).

C. plectostachyus is a grass cultivated as a forage species that has been established and has persisted in pastures across the tropics and which currently occupies a large area principally in wet areas. It can grow on a wide range of habitats and soil types and competes well with other grasses and weeds due to its aggressive growth and rapid propagation. It is a fast-growing grass characterized by a rapid elongation of stolons and a rapid production and death of leaves, displacing native vegetation and generating large accumulation of dry-matter biomass associated with changes in fuel load and fire regimes in invaded habitats (Barkworth, 2003; Heuzé et al., 2015; PROTA, 2015). C. plectostachyus recovers quickly after fire, and can even benefit from fire through spittlebug and disease control (FAO, 2015; Heuzé et al., 2015). Currently, C. plectostachyus is listed as invasive in California (USA), Cuba, and Brazil (Oviedo Prieto et al., 2012; I3N-Brasil, 2015; USDA-NRCS, 2015).

Twinfilin bypasses assembly conditions and actin filament aging to drive barbed end depolymerization

Cellular actin networks grow by ATP-actin addition at filament barbed ends and have long been presumed to depolymerize at their pointed ends, primarily after filaments undergo “aging” (ATP hydrolysis and Pi release). The cytosol contains high levels of actin monomers, which favors assembly over disassembly, and barbed ends are enriched in ADP-Pi actin. For these reasons, the potential for a barbed end depolymerization mechanism in cells has received little attention. Here, using microfluidics-assisted TIRF microscopy, we show that mouse twinfilin, a member of the ADF-homology family, induces depolymerization of ADP-Pi barbed ends even under assembly-promoting conditions. Indeed, we observe in single reactions containing micromolar concentrations of actin monomers the simultaneous rapid elongation of formin-bound barbed ends and twinfilin-induced depolymerization of free barbed ends. The data show that twinfilin catalyzes dissociation of subunits from ADP-Pi barbed ends and thereby bypasses filament aging prerequisites to disassemble newly polymerized actin filaments.

RYK-mediated filopodial pathfinding facilitates midgut elongation

ABSTRACTBetween embryonic days 10.5 and 14.5, active proliferation drives rapid elongation of the murine midgut epithelial tube. Within this pseudostratified epithelium, nuclei synthesize DNA near the basal surface and move apically to divide. After mitosis, the majority of daughter cells extend a long, basally oriented filopodial protrusion, building a de novo path along which their nuclei can return to the basal side. WNT5A, which is secreted by surrounding mesenchymal cells, acts as a guidance cue to orchestrate this epithelial pathfinding behavior, but how this signal is received by epithelial cells is unknown. Here, we have investigated two known WNT5A receptors: ROR2 and RYK. We found that epithelial ROR2 is dispensable for midgut elongation. However, loss of Ryk phenocopies the Wnt5a−/− phenotype, perturbing post-mitotic pathfinding and leading to apoptosis. These studies reveal that the ligand-receptor pair WNT5A-RYK acts as a navigation system to instruct filopodial pathfinding, a process that is crucial for continuous cell cycling to fuel rapid midgut elongation.