Floral organ abscission in Arabidopsis requires the combined activities of three TALE homeodomain transcription factors

Floral organ abscission is a separation process in which sepals, petals, and stamens detach from the plant at abscission zones. Here, we investigated the collective role of three amino-acid-loop-extension (TALE) homeobox genes ARABIDOPSIS THALIANA HOMEOBOX GENE1 (ATH1), KNAT6 (for KNOTTED LIKE from Arabidopsis thaliana) and KNAT2, which form a module that patterns boundaries under the regulation of BLADE-ON-PETIOLE 1 and 2 (BOP1/2) co-activators. These TALE homeodomain transcription factors were shown to maintain boundaries in the flower, functioning as a unit to coordinate the growth, patterning, and activity of abscission zones. Together with BOP1 and BOP2, ATH1 and its partners KNAT6 and KNAT2 collectively contribute to the differentiation of lignified and separation layers of the abscission zone. The genetic interactions of BOP1/2 and ATH1 with INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) were also explored. We showed that BOP1/2 co-activators and ATH1 converge with the IDA signalling pathway to promote KNAT6 and KNAT2 expression in the abscission zone and cell separation. ATH1 acts as a central regulator in floral organ abscission as it controls the expression of other TALE genes in abscission zone cells.

Drosophila Sex Peptide controls the assembly of lipid microcarriers in seminal fluid

Seminal fluid plays an essential role in promoting male reproductive success and modulating female physiology and behavior. In the fruit fly, Drosophila melanogaster, Sex Peptide (SP) is the best-characterized protein mediator of these effects. It is secreted from the paired male accessory glands (AGs), which, like the mammalian prostate and seminal vesicles, generate most of the seminal fluid contents. After mating, SP binds to spermatozoa and is retained in the female sperm storage organs. It is gradually released by proteolytic cleavage and induces several long-term postmating responses, including increased ovulation, elevated feeding, and reduced receptivity to remating, primarily signaling through the SP receptor (SPR). Here, we demonstrate a previously unsuspected SPR-independent function for SP. We show that, in the AG lumen, SP and secreted proteins with membrane-binding anchors are carried on abundant, large neutral lipid-containing microcarriers, also found in other SP-expressing Drosophila species. These microcarriers are transferred to females during mating where they rapidly disassemble. Remarkably, SP is a key microcarrier assembly and disassembly factor. Its absence leads to major changes in the seminal proteome transferred to females upon mating. Males expressing nonfunctional SP mutant proteins that affect SP's binding to and release from sperm in females also do not produce normal microcarriers, suggesting that this male-specific defect contributes to the resulting widespread abnormalities in ejaculate function. Our data therefore reveal a role for SP in formation of seminal macromolecular assemblies, which may explain the presence of SP in Drosophila species that lack the signaling functions seen in Dmelanogaster.

Metabarcoding of shrimp stomach content: Harnessing a natural sampler for fish biodiversity monitoring

Given their positioning and biological productivity, estuaries have long represented key providers of ecosystem services and consequently remain under remarkable pressure from numerous forms of anthropogenic impact. The monitoring of fish communities in space and time is one of the most widespread and established approaches to assess the ecological status of estuaries and other coastal habitats, but traditional fish surveys are invasive, costly, labour intensive and highly selective. Recently, the application of metabarcoding techniques, on either sediment or aqueous environmental DNA, has rapidly gained popularity. Here, we evaluate the application of a novel, high‐throughput DNA‐based monitoring tool to assess fish diversity, based on the analysis of the gut contents of a generalist predator/scavenger, the European brown shrimp, Crangon crangon. Sediment and shrimp samples were collected from eight European estuaries, and DNA metabarcoding (using both 12S and COI markers) was carried out to infer fish assemblage composition. We detected 32 teleost species (16 and 20, for 12S and COI, respectively). Twice as many species were recovered using metabarcoding than by traditional net surveys. By comparing and interweaving trophic, environmental DNA and traditional survey‐based techniques, we show that the DNA‐assisted gut content analysis of a ubiquitous, easily accessible, generalist species may serve as a powerful, rapid and cost‐effective tool for large‐scale, routine estuarine biodiversity monitoring.

Repression of BLADE-ON-PETIOLE genes by KNOX homeodomain protein BREVIPEDICELLUS is essential for differentiation of secondary xylem in Arabidopsis root

Repression of boundary genes by KNOTTED1-like homeodomain transcription factor BREVIPEDICELLUS promotes the differentiation of phase II secondary xylem in Arabidopsis roots. Plant growth and development relies on the activity of meristems. Boundaries are domains of restricted growth that separate forming organs and the meristem. Class I KNOX homeodomain transcription factors are important regulators of meristem maintenance. Members of this class including BREVIDICELLUS also called KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (BP/KNAT1) fulfill this function in part by spatially regulating boundary genes. The vascular cambium is a lateral meristem that allows for radial expansion of organs during secondary growth. We show here that BP/KNAT1 repression of boundary genes plays a crucial role in root secondary growth. In particular, exclusion of BLADE-ON-PETIOLE1/2 (BOP1/2) and other members of this module from xylem is required for the differentiation of lignified fibers and vessels during the xylem expansion phase of root thickening. These data reveal a previously undiscovered role for boundary genes in the root and shed light on mechanisms controlling wood development in trees.

Regulation of Dense-Core Granule Replenishment by Autocrine BMP Signalling in Drosophila Secondary Cells

Regulated secretion by glands and neurons involves release of signalling molecules and enzymes selectively concentrated in dense-core granules (DCGs). Although we understand how many secretagogues stimulate DCG release, how DCG biogenesis is then accelerated to replenish the DCG pool remains poorly characterised. Here we demonstrate that each prostate-like secondary cell (SC) in the paired adult Drosophila melanogaster male accessory glands contains approximately ten large DCGs, which are loaded with the Bone Morphogenetic Protein (BMP) ligand Decapentaplegic (Dpp). These DCGs can be marked in living tissue by a glycophosphatidylinositol (GPI) lipid-anchored form of GFP. In virgin males, BMP signalling is sporadically activated by constitutive DCG secretion. Upon mating, approximately four DCGs are typically released immediately, increasing BMP signalling, primarily via an autocrine mechanism. Using inducible knockdown specifically in adult SCs, we show that secretion requires the Soluble NSF Attachment Protein, SNAP24. Furthermore, mating-dependent BMP signalling not only promotes cell growth, but is also necessary to accelerate biogenesis of new DCGs, restoring DCG number within 24 h. Our analysis therefore reveals an autocrine BMP-mediated feedback mechanism for matching DCG release to replenishment as secretion rates fluctuate, and might explain why in other disease-relevant systems, like pancreatic β-cells, BMP signalling is also implicated in the control of secretion.

BMP-regulated exosomes from Drosophila male reproductive glands reprogram female behavior

Male Drosophila reproductive glands secrete exosomes in a BMP-dependent manner that fuse with sperm after mating and suppress female remating.

Male reproductive glands secrete signals into seminal fluid to facilitate reproductive success. In Drosophila melanogaster, these signals are generated by a variety of seminal peptides, many produced by the accessory glands (AGs). One epithelial cell type in the adult male AGs, the secondary cell (SC), grows selectively in response to bone morphogenetic protein (BMP) signaling. This signaling is involved in blocking the rapid remating of mated females, which contributes to the reproductive advantage of the first male to mate. In this paper, we show that SCs secrete exosomes, membrane-bound vesicles generated inside late endosomal multivesicular bodies (MVBs). After mating, exosomes fuse with sperm (as also seen in vitro for human prostate-derived exosomes and sperm) and interact with female reproductive tract epithelia. Exosome release was required to inhibit female remating behavior, suggesting that exosomes are downstream effectors of BMP signaling. Indeed, when BMP signaling was reduced in SCs, vesicles were still formed in MVBs but not secreted as exosomes. These results demonstrate a new function for the MVB–exosome pathway in the reproductive tract that appears to be conserved across evolution.

Evaluation and optimization of IgY spin column technology in the depletion of abundant proteins from human serum

Serum depletion strategies are commonly implemented in order to remove abundant proteins, increasing the number of proteins detected in a biomarker study. The IgY spin columns used in this study bind 12 and 14 primate proteins, respectively. 1-D SDS-PAGE and 2-DE revealed a suboptimal performance of the IgY spin columns. However, modification of the manufacturer's protocol, subjecting samples to two rounds of depletion, improved the number of proteins resolved by 2-DE. With alteration of the manufacturer protocol, the Seppro(®) IgY14 spin column can produce depleted serum with an increased number of spots resolved by 2-DE compared to untreated serum.

Bone strength index in adolescent girls: does physical activity make a difference?

BACKGROUND

Bone strength index (BSI) combines bone mineral and bone biomechanical properties to measure resistance to bending. This index may have greater clinical significance than the more often described markers of bone mineral content (BMC), areal density, or geometry alone and, in turn, may show a stronger relation to fracture risk. The BSI is the product of volumetric cortical bone mineral density (BMD) and cross sectional moment of inertia within a region of interest. Calculations combine dual energy x ray absorptiometry and magnetic resonance imaging technologies and provide a useful, non-invasive measure of in vivo bone strength.

OBJECTIVES

(a) To compare BSI in adolescent female middle distance runners and age matched controls; (b) to examine factors predictive of BSI in adolescent girls.

METHODS

Twenty adolescent female middle distance runners (mean (SD) age 16 (1.7) years, physical activity 8.9 (2.1) hours a week) and 20 female controls (age 16 (1.8) years, physical activity 2.0 (0.07) hours a week) were recruited. To calculate BSI, a region of interest representing 10% of the mid-distal tibia was analysed for dual energy x ray absorptiometry derived BMC and was combined with bone geometry and biomechanical properties obtained by magnetic resonance imaging assessments. Potential predictors of BSI were also examined.

RESULTS

Independent t tests showed that BMC (p = 0.028), cortical bone volume (p = 0.002), volumetric cortical BMD (p = 0.004), cross sectional moments of inertia (p = 0.005), and BSI (p = 0.002) were higher in the distal tibia of athletes than of controls. The strongest predictor of BSI was hours of physical activity a week (R2 = 0.46).

CONCLUSIONS

Athletes habitually exposed to high training loads displayed greater BSI at the distal tibia than controls. The results further confirm BSI as a significant and discerning marker in musculoskeletal health in adolescent girls engaged in high and low mechanical loading.