The Arabidopsis splicing factor PORCUPINE/SmE1 orchestrates temperature-dependent root development via auxin homeostasis maintenance.

Appropriate abiotic stress response is pivotal for plant survival and makes use of multiple signaling molecules and phytohormones to achieve specific and fast molecular adjustments. A multitude of studies has highlighted the role of alternative splicing in response to abiotic stress, including temperature, emphasizing the role of transcriptional regulation for stress response. Here we investigated the role of the core-splicing factor PORCUPINE (PCP) on temperature-dependent root development. We used marker lines and transcriptomic analyses to study the expression profiles of meristematic regulators and mitotic markers, and chemical treatments, as well as root hormone profiling to assess the effect of auxin signaling. The loss of PCP significantly alters RAM architecture in a temperature-dependent manner. Our results indicate that PCP modulates the expression of central meristematic regulators and is required to maintain appropriate levels of auxin in the RAM. We conclude that alternative pre-mRNA splicing is sensitive to moderate temperature fluctuations and contributes to root meristem maintenance, possibly through the regulation of phytohormone homeostasis and meristematic activity.

PICLN modulates alternative splicing and light/temperature responses in plants.

Plants undergo transcriptome reprograming to adapt to daily and seasonal fluctuations in light and temperature conditions. While most efforts have focused on the role of master transcription factors, the importance of splicing factors modulating these processes is now emerging. Efficient pre-mRNA splicing depends on proper spliceosome assembly, which in plants and animals requires the methylosome complex. Ion Chloride nucleotide-sensitive protein (PICLN) is part of the methylosome complex in both humans and Arabidopsis (Arabidopsis thaliana), and we show here that the human PICLN ortholog rescues phenotypes of Arabidopsis picln mutants. Altered photomorphogenic and photoperiodic responses in Arabidopsis picln mutants are associated with changes in pre-mRNA splicing that partially overlap with those in PROTEIN ARGININE METHYL TRANSFERASE5 (prmt5) mutants. Mammalian PICLN also acts in concert with the Survival Motor Neuron (SMN) complex component GEMIN2 to modulate the late steps of UsnRNP assembly, and many alternative splicing events regulated by PICLN but not PRMT5, the main protein of the methylosome, are controlled by Arabidopsis GEMIN2. As with GEMIN2 and SM PROTEIN E1/PORCUPINE (SME1/PCP), low temperature, which increases PICLN expression, aggravates morphological and molecular defects of picln mutants. Taken together, these results establish a key role for PICLN in the regulation of pre-mRNA splicing and in mediating plant adaptation to daily and seasonal fluctuations in environmental conditions.

From Soy Waste to Bioplastics: Industrial Proof of Concept.

The global plastic waste problem is pushing for the development of sustainable alternatives, encouraged by stringent regulations combined with increased environmental consciousness. In response, this study presents an industrial-scale proof of concept to produce self-standing, transparent, and flexible bioplastic films, offering a possible solution to plastic pollution and resource valorization. We achieve this by combining amyloid fibrils self-assembled from food waste with methylcellulose and glycerol. Specifically, soy whey and okara, two pivotal protein-rich byproducts of tofu manufacturing, emerge as sustainable and versatile precursors for amyloid fibril formation and bioplastic development. An exhaustive industrial-scale feasibility study involving the transformation of 500 L of soy whey into ∼1 km (27 kg) of bioplastic films underscores the potential of this technology. To extend the practicality of our approach, we further processed a running kilometer of film at the industrial scale into transparent windows for paper-based packaging. The mechanical properties and the water interactions of the novel film are tested and compared with those of commercially used plastic films. By pioneering the large-scale production of biodegradable bioplastics sourced from food byproducts, this work not only simultaneously addresses the dual challenges of plastic pollution and food waste but also practically demonstrates the feasibility of biopolymeric building block valorization for the development of sustainable materials in real-world scenarios.

The SHREAD gene therapy platform for paracrine delivery improves tumor localization and intratumoral effects of a clinical antibody.

The goal of cancer-drug delivery is to achieve high levels of therapeutics within tumors with minimal systemic exposure that could cause toxicity. Producing biologics directly in situ where they diffuse and act locally is an attractive alternative to direct administration of recombinant therapeutics, as secretion by the tumor itself provides high local concentrations that act in a paracrine fashion continuously over an extended duration (paracrine delivery). We have engineered a SHielded, REtargeted ADenovirus (SHREAD) gene therapy platform that targets specific cells based on chosen surface markers and converts them into biofactories secreting therapeutics. In a proof of concept, a clinically approved antibody is delivered to orthotopic tumors in a model system in which precise biodistribution can be determined using tissue clearing with passive CLARITY technique (PACT) with high-resolution three-dimensional imaging and feature quantification within the tumors made transparent. We demonstrate high levels of tumor cell-specific transduction and significant and durable antibody production. PACT gives a localized quantification of the secreted therapeutic and allows us to directly observe enhanced pore formation in the tumor and destruction of the intact vasculature. In situ production of the antibody led to an 1,800-fold enhanced tumor-to-serum antibody concentration ratio compared to direct administration. Our detailed biochemical and microscopic analyses thus show that paracrine delivery with SHREAD could enable the use of highly potent therapeutic combinations, including those with systemic toxicity, to reach adequate therapeutic windows.

Perturbations in plant energy homeostasis prime lateral root initiation via SnRK1-bZIP63-ARF19 signaling.

Plants adjust their energy metabolism to continuous environmental fluctuations, resulting in a tremendous plasticity in their architecture. The regulatory circuits involved, however, remain largely unresolved. In Arabidopsis, moderate perturbations in photosynthetic activity, administered by short-term low light exposure or unexpected darkness, lead to increased lateral root (LR) initiation. Consistent with expression of low-energy markers, these treatments alter energy homeostasis and reduce sugar availability in roots. Here, we demonstrate that the LR response requires the metabolic stress sensor kinase Snf1-RELATED-KINASE1 (SnRK1), which phosphorylates the transcription factor BASIC LEUCINE ZIPPER63 (bZIP63) that directly binds and activates the promoter of AUXIN RESPONSE FACTOR19 (ARF19), a key regulator of LR initiation. Consistently, starvation-induced ARF19 transcription is impaired in bzip63 mutants. This study highlights a positive developmental function of SnRK1. During energy limitation, LRs are initiated and primed for outgrowth upon recovery. Hence, this study provides mechanistic insights into how energy shapes the agronomically important root system.

Genomic selection strategies for the German Merino sheep breeding programme - A simulation study.

Genomic selection is widely implemented in livestock breeding programmes across species. Its potential is also evident for sheep breeding; however, it has several limitations, particularly because of the high genetic diversity across and within sheep breeds. In Germany, the predominant sheep breed is the Merino sheep. Until now, there has been no use of genomic selection in the German Merino sheep breeding programme. In this simulation study, different genomic selection strategies were compared with a reference scenario with a breeding value estimation based on pedigree BLUP. A simplified version of the German Merino sheep breeding programme, including a health and a production trait in the breeding goal, was simulated via the R package Modular Breeding Program Simulator (MoBPS). Real genotype data were used to create a population specific simulation. The reference scenario was compared with several alternative scenarios in which selection was based on single-step GBLUP (ssGBLUP) breeding value estimation with varying genotyping strategies. In addition to scenarios in which all male and all male plus all female lambs were genotyped, scenarios with a preselection of lambs, that is only a certain proportion (top 25%, top 50%) genotyped, were simulated. The results revealed that genetic gain increased with increasing numbers of available genotypes. However, marginal gains decreased with increasing numbers of genotypes. Compared with the reference scenario, genotyping the top 25% of male lambs increased the genetic gain for the breeding ram population by 13% for both traits whereas genotyping the top 50% of male lambs or all male lambs led to increases of 18% (17%) or 26% (21%) for the health (production) trait, respectively. The potential of genotyping females in addition to male lambs was less evident on the male side with no significant differences between the scenarios with different proportions of genotyped females. The results have shown that genomic selection can be a valuable tool to increase genetic gain in the German Merino sheep population and that the genotyping of a certain proportion of animals might lead to substantial improvement over pedigree-based breeding value estimation. Nevertheless, further studies, especially economic evaluations, are needed before practical implementation.

Genomic analyses of nitrogen utilization efficiency, its indicator trait blood urea nitrogen and the relationship to classical growth performance and feed efficiency traits in a Landrace × Piétrain crossbred population.

Improving the nutrient efficiency in pork production is required to reduce the resource competition between human food and animal feed regarding diet components edible for humans and to minimize emissions relevant to climate or the environment. Thereby, protein utilization efficiency and its equivalent nitrogen utilization efficiency (NUE) play a major role. Breeding for more nitrogen (N) efficient pigs bears a promising strategy to improve such traits, however, directly phenotyping NUE based on N balance data is neither cost-efficient nor straightforward and not applicable for routine evaluations. Blood urea nitrogen (BUN) levels in the pig are suitable to predict the NUE and, therefore, might be an indicator trait for NUE because BUN is a relatively easy-to-measure trait. This study investigated the suitability of NUE as a selection trait in future breeding programs. The relationships to classical growth performance and feed efficiency traits were analysed as well as the relationship to BUN to infer the role of BUN as an indicator trait to improve NUE via breeding. The analyzes were based on a Landrace F1 cross population consisting of 502 individuals who descended from 20 Piétrain sires. All animals were genotyped for 48,525 SNPs. They were phenotyped in two different fattening phases, i.e., FP1 and FP2, during the experiment. Uni- and bivariate analyses were run to estimate variance components and to determine the genetic correlation between different traits or between the same trait measured at different time points. Moderate heritabilities were estimated for all traits, whereby the heritability for NUE was h2 = 0.293 in FP1 and h2 = 0.163 in FP2 and BUN had the by far highest heritability (h2 = 0.415 in FP1 and h2 = 0.460 in FP2). The significant genetic correlation between NUE and BUN showed the potential of BUN to be considered an indicator trait for NUE. This was particularly pronounced when NUE was measured in FP1 (genetic correlations r g = - 0.631 and r g = - 0.688 between NUE and BUN measured in FP1 and FP2, respectively). The genetic correlations of NUE and BUN with important production traits suggest selecting pigs with high growth rates and low BUN levels to breed more efficient pigs in future breeding programs.

Exo- and endophytic fungi enable rapid transfer of nutrients from ant waste to orchid tissue.

The epiphytic orchid Caularthron bilamellatum sacrifices its water storage tissue for nutrients from the waste of ants lodging inside its hollow pseudobulb. Here, we investigate whether fungi are involved in the rapid translocation of nutrients. Uptake was analysed with a 15 N labelling experiment, subsequent isotope ratio mass spectrometry (IRMS) and secondary ion mass spectrometry (ToF-SIMS and NanoSIMS). We encountered two hyphae types: a thick melanized type assigned to 'black fungi' (Chaetothyriales, Cladosporiales, and Mycosphaerellales) in ant waste, and a thin endophytic type belonging to Hypocreales. In few cell layers, both hyphae types co-occurred. 15 N accumulation in both hyphae types was conspicuous, while for translocation to the vessels only Hypocreales were involved. There is evidence that the occurrence of the two hyphae types results in a synergism in terms of nutrient uptake. Our study provides the first evidence that a pseudobulb (=stem)-born endophytic network of Hypocreales is involved in the rapid translocation of nitrogen from insect-derived waste to the vegetative and reproductive tissue of the host orchid. For C. bilamellatum that has no contact with the soil, ant waste in the hollow pseudobulbs serves as equivalent to soil in terms of nutrient sources.

Is the Femoral-Epiphyseal Acetabular Roof (FEAR) index associated with hip pain in patients with hip dysplasia?

BACKGROUND: Micro instability of the hip joint has been suggested to cause pain in patients with hip dysplasia. Recently, the Femoral-Epiphyseal Acetabular Roof (FEAR) index has been developed to evaluate hip instability in patients with dysplasia. PURPOSE: To investigate associations between the FEAR index and patient-reported outcomes before and six months after periacetabular osteotomy (PAO). MATERIAL AND METHODS: Radiographs of patients with hip dysplasia who underwent PAO between 2018 and 2020 were retrospectively assessed by a radiologist and an orthopedic surgeon. Radiographic measurements indicative of hip instability (Shenton's line, FEAR index, center-edge angle of Wiberg, acetabular index of Tönnis, and the femoral neck-shaft angle) were measured. Data on hip pain, function, and quality of life were collected prospectively using the Hip dysfunction and Osteoarthritis Outcome Score (HOOS). RESULTS: A total of 222 patients were included in the study. All radiographic measurements and patient-reported outcomes improved significantly from preoperative to six months postoperative (P < 0.001). There were no differences in the change score of patient-reported outcomes between patients with a FEAR index >2° (indicative of hip instability) and patients with a FEAR index ≤2°. CONCLUSION: The FEAR index was not associated with hip pain, function, and quality of life among patients with hip dysplasia. This study did not find evidence supporting that instability defined by the FEAR index caused pain in patients with hip dysplasia.

Impaired KIN10 function restores developmental defects in the Arabidopsis trehalose 6-phosphate synthase1 (tps1) mutant.

Sensing carbohydrate availability is essential for plants to coordinate their growth and development. In Arabidopsis thaliana, TREHALOSE 6-PHOSPHATE SYNTHASE 1 (TPS1) and its product, trehalose 6-phosphate (T6P), are important for the metabolic control of development. tps1 mutants are embryo-lethal and unable to flower when embryogenesis is rescued. T6P regulates development in part through inhibition of SUCROSE NON-FERMENTING1 RELATED KINASE1 (SnRK1). Here, we explored the role of SnRK1 in T6P-mediated plant growth and development using a combination of a mutant suppressor screen and genetic, cellular and transcriptomic approaches. We report nonsynonymous amino acid substitutions in the catalytic KIN10 and regulatory SNF4 subunits of SnRK1 that can restore both embryogenesis and flowering of tps1 mutant plants. The identified SNF4 point mutations disrupt the interaction with the catalytic subunit KIN10. Contrary to the common view that the two A. thaliana SnRK1 catalytic subunits act redundantly, we found that loss-of-function mutations in KIN11 are unable to restore embryogenesis and flowering, highlighting the important role of KIN10 in T6P signalling.

Phloem Companion Cell-Specific Transcriptomic and Epigenomic Analyses Identify MRF1, a Regulator of Flowering.

The phloem plays essential roles in the source-to-sink relationship and in long-distance communication, and thereby coordinates growth and development throughout the plant. Here we employed isolation of nuclei tagged in specific cell types coupled with low-input, high-throughput sequencing approaches to analyze the changes of the chromatin modifications H3K4me3 and H3K27me3 and their correlation with gene expression in the phloem companion cells (PCCs) of Arabidopsis(Arabidopsis thaliana) shoots in response to changes in photoperiod. We observed a positive correlation between changes in expression and H3K4me3 levels of genes that are involved in essential PCC functions, including regulation of metabolism, circadian rhythm, development, and epigenetic modifications. By contrast, changes in H3K27me3 signal appeared to contribute little to gene expression changes. These genomic data illustrate the complex gene-regulatory networks that integrate plant developmental and physiological processes in the PCCs. Emphasizing the importance of cell-specific analyses, we identified a previously uncharacterized MORN-motif repeat protein, MORN-MOTIF REPEAT PROTEIN REGULATING FLOWERING1 (MRF1), that was strongly up-regulated in the PCCs in response to inductive photoperiod. The mrf1 mutation delayed flowering, whereas MRF1 overexpression had the opposite effect, indicating that MRF1 acts as a floral promoter.

On the evolution and physiology of cable bacteria.

Cable bacteria of the family Desulfobulbaceae form centimeter-long filaments comprising thousands of cells. They occur worldwide in the surface of aquatic sediments, where they connect sulfide oxidation with oxygen or nitrate reduction via long-distance electron transport. In the absence of pure cultures, we used single-filament genomics and metagenomics to retrieve draft genomes of 3 marine Candidatus Electrothrix and 1 freshwater Ca. Electronema species. These genomes contain >50% unknown genes but still share their core genomic makeup with sulfate-reducing and sulfur-disproportionating Desulfobulbaceae, with few core genes lost and 212 unique genes (from 197 gene families) conserved among cable bacteria. Last common ancestor analysis indicates gene divergence and lateral gene transfer as equally important origins of these unique genes. With support from metaproteomics of a Ca. Electronema enrichment, the genomes suggest that cable bacteria oxidize sulfide by reversing the canonical sulfate reduction pathway and fix CO2 using the Wood-Ljungdahl pathway. Cable bacteria show limited organotrophic potential, may assimilate smaller organic acids and alcohols, fix N2, and synthesize polyphosphates and polyglucose as storage compounds; several of these traits were confirmed by cell-level experimental analyses. We propose a model for electron flow from sulfide to oxygen that involves periplasmic cytochromes, yet-unidentified conductive periplasmic fibers, and periplasmic oxygen reduction. This model proposes that an active cable bacterium gains energy in the anodic, sulfide-oxidizing cells, whereas cells in the oxic zone flare off electrons through intense cathodic oxygen respiration without energy conservation; this peculiar form of multicellularity seems unparalleled in the microbial world.

Olive byproducts and their bioactive compounds as a valuable source for food packaging applications.

Among the most important agro-industrial activities in the Mediterranean basin, olive oil production has a high impact on the economy of many Mediterranean countries. However, olive oil extraction generates huge quantities of byproducts, including leaves, pomace residues, stones and wastewater, which have severe environmental impacts mainly because of their phytotoxicity and great organic content. Olive oil byproducts are regarded as inexpensive and abundant raw materials rich in bioactive compounds with high and varied health-related activities. Several phenolic compounds and terpenoids were recovered from olive byproducts using different conventional and advanced extraction methods due to their potential to be used in food, packaging, pharmaceutical, and cosmetic industries. Recently, the use of olive byproducts and their functional compounds to enhance the functional properties of packaging systems was investigated as a sustainable strategy for food preservation, fostering the sustainability of the olive-oil chain, and promoting circular economy. In this framework, the main goals of this review are to summarize the main bioactive compounds in olive byproducts, to review the main advancements in their extraction, purification, and characterization, and finally to discuss their applications in food packaging systems as well as safety-related aspects.

The trehalose 6-phosphate pathway impacts vegetative phase change in Arabidopsis thaliana.

The vegetative phase change marks the beginning of the adult phase in the life cycle of plants and is associated with a gradual decline in the microRNA miR156, in response to sucrose status. Trehalose 6-phosphate (T6P) is a sugar molecule with signaling function reporting the current sucrose state. To elucidate the role of T6P signaling in vegetative phase change, molecular, genetic, and metabolic analyses were performed using Arabidopsis thaliana loss-of-function lines in TREHALOSE PHOSPHATE SYNTHASE1 (TPS1), a gene coding for an enzyme that catalyzes the production of T6P. These lines show a significant delay in vegetative phase change, under both short and long day conditions. Induced expression of TPS1 complements this delay in the TPS1 knockout mutant (tps1-2 GVG::TPS1). Further analyses indicate that the T6P pathway promotes vegetative phase transition by suppressing miR156 expression and thereby modulating the levels of its target transcripts, the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE genes. TPS1 knockdown plants, with a delayed vegetative phase change phenotype, accumulate significantly more sucrose than wild-type plants as a result of a feedback mechanism. In summary, we conclude that the T6P pathway forms an integral part of an endogenous mechanism that influences phase transitions dependent on the metabolic state.

Lactoferrin-Hexon Interactions Mediate CAR-Independent Adenovirus Infection of Human Respiratory Cells.

Virus entry into host cells is a complex process that is largely regulated by access to specific cellular receptors. Human adenoviruses (HAdVs) and many other viruses use cell adhesion molecules such as the coxsackievirus and adenovirus receptor (CAR) for attachment to and entry into target cells. These molecules are rarely expressed on the apical side of polarized epithelial cells, which raises the question of how adenoviruses-and other viruses that engage cell adhesion molecules-enter polarized cells from the apical side to initiate infection. We have previously shown that species C HAdVs utilize lactoferrin-a common innate immune component secreted to respiratory mucosa-for infection via unknown mechanisms. Using a series of biochemical, cellular, and molecular biology approaches, we mapped this effect to the proteolytically cleavable, positively charged, N-terminal 49 residues of human lactoferrin (hLF) known as human lactoferricin (hLfcin). Lactoferricin (Lfcin) binds to the hexon protein on the viral capsid and anchors the virus to an unknown receptor structure of target cells, resulting in infection. These findings suggest that HAdVs use distinct cell entry mechanisms at different stages of infection. To initiate infection, entry is likely to occur at the apical side of polarized epithelial cells, largely by means of hLF and hLfcin bridging HAdV capsids via hexons to as-yet-unknown receptors; when infection is established, progeny virions released from the basolateral side enter neighboring cells by means of hLF/hLfcin and CAR in parallel.IMPORTANCE Many viruses enter target cells using cell adhesion molecules as receptors. Paradoxically, these molecules are abundant on the lateral and basolateral side of intact, polarized, epithelial target cells, but absent on the apical side that must be penetrated by incoming viruses to initiate infection. Our study provides a model whereby viruses use different mechanisms to infect polarized epithelial cells depending on which side of the cell-apical or lateral/basolateral-is attacked. This study may also be useful to understand the biology of other viruses that use cell adhesion molecules as receptors.

TERMINAL FLOWER1 Functions as a Mobile Transcriptional Cofactor in the Shoot Apical Meristem.

The floral transition is a critical step in the life cycle of flowering plants, and several mechanisms control this finely orchestrated process. TERMINAL FLOWER1 (TFL1) is a floral repressor and close relative of the florigen, FLOWERING LOCUS T (FT). During the floral transition, TFL1 expression is up-regulated in the inflorescence apex to maintain the indeterminate growth of the shoot apical meristem (SAM). Both TFL1 and FT are mobile proteins, but they move in different ways. FT moves from the leaves to the SAM, while TFL1 appears to move within the SAM. The importance of TFL1 movement for its function in the regulation of flowering time and shoot indeterminacy and its molecular function are still largely unclear. Our results using Arabidopsis (Arabidopsis thaliana) indicate that TFL1 moves from its place of expression in the center of the SAM to the meristem layer L1 and that the movement in the SAM is required for the regulation of the floral transition. Chromatin immunoprecipitation sequencing and RNA sequencing demonstrated that TFL1 functions as a cotranscription factor that associates with and regulates the expression of hundreds of genes. These newly identified direct TFL1 targets provide the possibility to discover new roles for TFL1 in the regulation of floral transition and inflorescence development.

Epigenetic Regulation of Temperature Responses - Past Successes and Future Challenges.

In contrast to animals, plants cannot avoid unfavorable temperature conditions. Instead, plants have evolved intricate signaling pathways that enable them to perceive and respond to temperature. General acclimation processes that prepare the plant to respond to stressful heat and cold, usually occur throughout the whole plant. More specific temperature responses, however, are limited to certain tissues or cell types. While global responses are amenable to epigenomic analyses, responses which are highly localized are more problematic as the chromatin in question is not easily accessible. Here we review the current knowledge of the epigenetic regulation of FLOWERING LOCUS C and FLOWERING LOCUS T as examples of temperature-responsive flowering time regulators that are expressed broadly throughout the plants and in specific cell types, respectively. While undoubtably extremely successful, we reason that future analyses would benefit from higher spatiotemporal resolution. We conclude by reviewing methods and successful applications of tissue- and cell type-specific epigenomic analyses and provide a brief outlook into the future, single-cell epigenomics.

Insights into the role of alternative splicing in plant temperature response.

Alternative splicing occurs in all eukaryotic organisms. Since the first description of multiexon genes and the splicing machinery, the field has expanded rapidly, especially in animals and yeast. However, our knowledge about splicing in plants is still quite fragmented. Though eukaryotes show some similarity in the composition and dynamics of the splicing machinery, observations of unique plant traits are only starting to emerge. For instance, plant alternative splicing is closely linked to their ability to perceive various environmental stimuli. Due to their sessile lifestyle, temperature is a central source of information allowing plants to adjust their development to match current growth conditions. Hence, seasonal temperature fluctuations and day-night cycles can strongly influence plant morphology across developmental stages. Here we discuss the available data about temperature-dependent alternative splicing in plants. Given its fragmented state it is not always possible to fit specific observations into a coherent picture, yet it is sufficient to estimate the complexity of this field and the need of further research. Better understanding of alternative splicing as a part of plant temperature response and adaptation may also prove to be a powerful tool for both, fundamental and applied sciences.

WRKY23 is a component of the transcriptional network mediating auxin feedback on PIN polarity.

Auxin is unique among plant hormones due to its directional transport that is mediated by the polarly distributed PIN auxin transporters at the plasma membrane. The canalization hypothesis proposes that the auxin feedback on its polar flow is a crucial, plant-specific mechanism mediating multiple self-organizing developmental processes. Here, we used the auxin effect on the PIN polar localization in Arabidopsis thaliana roots as a proxy for the auxin feedback on the PIN polarity during canalization. We performed microarray experiments to find regulators of this process that act downstream of auxin. We identified genes that were transcriptionally regulated by auxin in an AXR3/IAA17- and ARF7/ARF19-dependent manner. Besides the known components of the PIN polarity, such as PID and PIP5K kinases, a number of potential new regulators were detected, among which the WRKY23 transcription factor, which was characterized in more detail. Gain- and loss-of-function mutants confirmed a role for WRKY23 in mediating the auxin effect on the PIN polarity. Accordingly, processes requiring auxin-mediated PIN polarity rearrangements, such as vascular tissue development during leaf venation, showed a higher WRKY23 expression and required the WRKY23 activity. Our results provide initial insights into the auxin transcriptional network acting upstream of PIN polarization and, potentially, canalization-mediated plant development.

Long-distance electron transport in individual, living cable bacteria.

Electron transport within living cells is essential for energy conservation in all respiring and photosynthetic organisms. While a few bacteria transport electrons over micrometer distances to their surroundings, filaments of cable bacteria are hypothesized to conduct electric currents over centimeter distances. We used resonance Raman microscopy to analyze cytochrome redox states in living cable bacteria. Cable-bacteria filaments were placed in microscope chambers with sulfide as electron source and oxygen as electron sink at opposite ends. Along individual filaments a gradient in cytochrome redox potential was detected, which immediately broke down upon removal of oxygen or laser cutting of the filaments. Without access to oxygen, a rapid shift toward more reduced cytochromes was observed, as electrons were no longer drained from the filament but accumulated in the cellular cytochromes. These results provide direct evidence for long-distance electron transport in living multicellular bacteria.