Biology subjects

Feil, R.

Publications and source records attributed to Feil, R..

At least 19 recordsLinked to original sources

bioRxiv2026

C4 photosynthetic pathway fluxes in transgenic rice plants

Most land plants photosynthesize using the C3 pathway, in which ribulose bisphosphate carboxylase/oxygenase (Rubisco) fixes CO2 into 3-carbon acids. The C4 pathway, a biochemical CO2-concentrating mechanism that operates in the context of specialized leaf anatomy to concentrate CO2 around Rubisco, is more efficient. Introduction of the C4 pathway into the C3 crop rice could increase yield by 50%. Expression of five C4 enzymes in transgenic rice previously led to flux through the first step. However, there was no evidence for flux later in the cycle. Here we developed new transgenic rice lines and novel protocols to detect C4 cycle activity: CO2 fixation into C4 acids by carboxylation of a C3 compound, decarboxylation, refixation of CO2 by Rubisco, and regeneration of the C3 donor. We demonstrate that these four core C4 reactions are operating in rice, establishing the in vivo flux framework needed to progress towards a functional carbon-concentrating mechanism

plant biology↗

bioRxiv2026

Arteriolar GMP signaling revealed by FRET-based real-time measurement in vivo

cGMP evokes arteriolar vasorelaxation and is generated in smooth muscle by the soluble guanylyl cyclase (sGC) stimulated by endothelial NO. Phosphodiesterases (PDEs) degrade cGMP and may contribute in diameter regulation. We examined arteriolar cGMP levels in real-time in vivo upon NO and acetylcholine (ACh) and effects of PDE inhibition. Changes in cGMP were measured by FRET using the indicator protein cGi500. Arterioles in the cremaster muscle of anesthetized mice expressing cGi500 were exposed for imaging. They were stimulated with various NO donors (DEA/NO, SNP, SNAP) and ACh with or without PDE inhibition (non-specific: IBMX; PDE-5 specific: sildenafil). Furthermore, dilations induced by ACh and SNP were studied in sGC-deficient mice. DEA/NO and SNAP led to a fast, concentration-dependent rise of fluorescence ratio of cGi500 (by 4.0% at 10{micro}M), that declined on removal slowly. These ratio changes indicated cGMP increases as verified by inhibition of the sGC using ODQ. PDE inhibition increased cGMP levels slowly despite NO synthase inhibition. However, it did not amplify NO-induced ratio increases, but the decline after drug removal was decelerated. Interestingly, ACh did not modify cGMP levels and dilations were not impaired in sGC-deficient mice. FRET-based imaging allows reliable real-time assessment of arteriolar cGMP levels in vivo. PDE activity does not limit the amplitude, but the duration of cGMP signaling after stimulation. Furthermore, we conclude that ACh does not release endothelial NO in murine arterioles. Preliminary experiments demonstrate that simultaneous measurement of cGMP and diameter is feasible using mice with expression of cGi500 in smooth muscle cells.

physiology↗

bioRxiv2026

Transient uncoupling of the Suc-Tre6P-SnRK1 nexus during salt stress associates with biphasic metabolic reprogramming and root plasticity

Soil salinization threatens global agriculture reducing yields, yet the metabolic signals controlling salt-sensitive root plasticity in alfalfa remain unclear. We hypothesize that salinity transiently uncouples the sucrose-trehalose-6-P (Tre6P)- Sucrose non-fermenting kinase 1 (SnRK1) nexus, aligning with a biphasic root metabolic response and altered root architecture. Alfalfa seedlings were grown in a hydroponic system and exposed to 200 mM NaCl, with root samples collected from 1 h to 7 d. While primary root growth and biomass remained unchanged, lateral root development was enhanced under salinity. Early response (1 h-1 d) was characterized by reduced carbon metabolites, low Tre6P, increased malondialdehyde, and SnRK1 activation, with a decline in glycolytic and TCA intermediates. During this phase, sucrose was negatively correlated with both Tre6P and SnRK1. Late response (3-7 d) showed a SnRK1 reactivation, Tre6P recovery, and osmoprotectant accumulation, including increased antioxidant capacity (+75% at 3dpt), proline (+178%), and sucrose (+18%) and starch depletion (-57%) at 7dpt respect to control. These metabolic changes coincided with the enhanced lateral root emergence. These findings indicate a two-phase response: early metabolic downscaling with transient Suc-Tre6P-SnRK1 disruption, followed by recovery with Tre6P restoration, SnRK1 reactivation, osmoprotection, and sustained root plasticity under salinity. HighlightSalinity triggers a temporary metabolic shift in alfalfa roots: plants first conserve energy, then adapt to stress, maintaining lateral root growth and flexible root architecture.

plant biology↗

bioRxiv2026

Intercellular Concentration Gradients of 3-Phosphoglycerate and Triose-Phosphate Demonstrate Operation of an Energy Shuttle in NAD-Malic Enzyme and Phosphoenolypyruvate Carboxykinase C4 Subtypes

In C4 photosynthesis, incoming CO2 is incorporated in mesophyll cells (MC) into 4-carbon acids that diffuse to bundle sheath cells (BSC) and decarboxylated to generate a high CO2 concentration that suppresses the oxygenation reaction of Rubisco. Decarboxylation can occur by NADP-malic enzyme, (NADP-ME), NAD-malic enzyme (NAD-ME) or phosphoenolpyruvate carboxykinase (PEPCK). NADP-ME generates NADPH in the BSC chloroplast and species that use it as the major route for decarboxylation typically have dimorphic BSC chloroplasts with little or no photosystem II. They operate an energy shuttle: much of the 3-phosphoglycerate formed in the Calvin-Benson cycle diffuses to the MC, enters the chloroplasts and is reduced to triose phosphates that return to the BSC. In species where carboxylation occurs mainly via NAD-ME or PEPCK, BSC chloroplasts possess photosystem II. Indirect evidence indicates they nevertheless have the capacity to operate an energy shuttle. We show here that NAD-ME and PEPCK species possess large pools of 3PGA and triose phosphates and, for two examples of each subtype, opposed concentration gradients of 3-phosphoglycerate and triose phosphates to drive rapid exchange between the BSC and MC. Reasons for and consequences of the widespread operation of the intercellular energy shuttle in C4 plants are discussed. Highlight StatementAn intercellular energy shuttle in which 3-phosphoglycerate moves from the bundle sheath to the mesophyll and triose phosphates return to the bundle sheath is a general feature of C4 photosynthesis.

plant biology↗

bioRxiv2025

TPS Proteins coordinate plant growth with sugar availability via the SnRK1 Kinase

The ability to sense and respond to nutrients determines adaptation and survival in all organisms. In plants, sucrose stimulates growth and developmental progression via the signalling sugar trehalose 6-phosphate (T6P) which reflects sucrose availability. T6P acts, at least partly, by inhibiting the protein kinase SUCROSE NON-FERMENTING 1 (SNF1)-RELATED KINASE 1 (SnRK1) but the underlying mechanisms are poorly understood. Here, we identify a group of catalytically inactive T6P synthase (TPS) proteins, TPS5/6/7, as important factors for coupling the T6P signal to SnRK1 activity. In Arabidopsis thaliana, lack of TPS5/6/7 causes severe growth defects, particularly in roots. This is accompanied by a metabolic signature that is suggestive of T6P insensitivity and impaired sucrose utilization. Using a combination of genetics, SnRK1 activity assays, and imaging, we demonstrate that the growth defects of the tps5/6/7 mutant are due to SnRK1 misregulation and are reverted by knocking-down SnRK1 in this background. Co-immunoprecipitation assays further show that T6P promotes the interaction of TPS proteins with SnRK1 in a highly specific and dose-dependent manner. Our results support a model where TPS proteins act as T6P sensors, inhibiting non-nuclear SnRK1 activity when sucrose is abundant to promote biosynthetic processes and growth.

plant biology↗

bioRxiv2025

Exploring the diversity of the CO2-concentrating mechanism (CCM) in different C4 subtypes

C4 plants have traditionally been classified into NADP-malic enzyme (NADP-ME), NAD-malic enzyme (NAD-ME) and PEP carboxykinase (PEPCK) subtypes based on the predominant C4-acid decarboxylating enzyme. To investigate the relative contributions of malate and aspartate to C4-pathway fluxes in each subtype, we performed 13CO2 pulse and pulse-chase labelling experiments on four C4 grass species: Zea mays and Setaria viridis (NADP-ME), Panicum miliaceum (NAD-ME) and Megathyrsus maximus (PEPCK). Only a proportion (8-50%) of the total malate pool in the leaves is photosynthetically active whereas essentially all of the aspartate pool is photosynthetically active. Estimates of metabolic fluxes indicate that approximately two thirds of the C4 pathway flux is via malate in Z. mays and the remaining third via aspartate, while in S. viridis 50% of the flux is via malate and 50% via aspartate. In P. miliaceum and M. maximus, 91% and 85% of the flux is via aspartate and the remaining 5% and 15% via malate, respectively. The results reveal greater complexity of C4 pathway fluxes than is usually represented in textbook diagrams, and demonstrate the feasibility of using non-radioactive 13CO2 in pulse-chase labelling experiments to study C4 photosynthesis and to detect C4 pathway fluxes in C3 plants engineered to perform C4 photosynthesis. Highlight StatementPhotosynthetic fluxes in C4 species are more complex than most textbook models show, with malate and aspartate both carrying C4 cycle fluxes in all three subtypes (NADP-ME, NAD-ME and PEPCK).

plant biology↗

bioRxiv2025

Overcoming extensive redundancy in the arabidopsis TREHALOSE-6-PHOSPHATE PHOSPHATASE gene family reveals connections to development

Arabidopsis encodes ten TREHALOSE-6-PHOSPHATE PHOSPHATASE (TPP) genes, homologous to maize RAMOSA3 (I), which controls shoot branching. To explore the roles of the arabidopsis TPPs, we analyzed their expression in shoot apices and found distinct spatial patterns, including TPPI and TPPJ expressed in shoot meristem boundaries, reminiscent of RA3 expression. Single and double TPP mutants lacked dramatic phenotypes, however a CRISPR-Cas9 knockout of all ten TPP genes resulted in increased branching, mirroring ra3 mutants in maize, as well as reduced size and earlier flowering. Expression of GFP-tagged TPPI under its native promoter partially complemented these defects, with protein localization in meristems, vascular tissues and in nuclei. Metabolite profiling revealed higher trehalose 6-phosphate (Tre6P), lower trehalose, and altered sugar and iron-associated metabolites. The mutants also developed chlorosis and grew poorly on low-nutrient media, linked to low iron levels, and reversible with iron supplementation. Consistent with these findings, developmental and iron-responsive genes were up-regulated in the mutants, while photosynthesis-related genes were repressed. Our findings suggest that TPP genes redundantly regulate shoot architecture, sugar metabolism, iron homeostasis and photosynthesis in arabidopsis, and support a role for TPP-mediated Tre6P signaling in coordinating developmental and physiological pathways.

plant biology↗

bioRxiv2025

Seasonal changes in the physiology and metabolism of grapevine perennating buds

Grapevine (Vitis vinifera L.) buds undergo seasonal dormancy to survive unfavourable conditions and synchronize growth with environmental cues. While dormancy transitions have been widely studied in temperate woody perennials, the physiological and metabolic dynamics underlying these transitions in grapevine remain poorly understood. Our study investigates seasonal changes in the physiology and metabolism of perennating buds in V. vinifera cv. Cabernet Sauvignon, focusing on dormancy depth, respiration, sugar metabolism, and cell cycle activity. We identified three distinct phases of bud quiescence: (i) para-dormancy (early summer), characterized by active metabolism and high levels of tricarboxylic acid cycle intermediates, shikimate, and myo-inositol; (ii) endo-dormancy (late summer to autumn), where dormancy depth peaked in late summer and was marked by reduced respiration and bud water content, and a sharp decline in hexose levels with a concomitant increase in raffinose; and (iii) eco-dormancy (winter to spring), featuring increased respiration, sugar mobilization (notably sucrose, glucose, and trehalose), and reactivation of cell division, with a shift of cells into the G2 phase. Just prior to bud burst, we observed a significant accumulation of sugar-phosphates, providing evidence that supports their role in promoting bud burst also in grapevine. Our findings provide new insights into the biochemical and physiological regulation of bud dormancy and bud burst, contributing to a deeper understanding of dormancy transitions in perennial crops.

plant biology↗

bioRxiv2025

Too much sugar makes plants "pregnant": maternal sucrose signals fertilization in Arabidopsis seeds

Reproduction is deemed successful if it ensures the perpetuation of the species. Nonetheless, evolution has optimized reproductive efficiency across a diverse range of strategies. Animal vivipary, the process in which embryos develop inside the parents body, allows for larger offspring and better protection. This reproductive strategy relies on a fertilization signal sent to the maternal tissues to establish an embryo-supportive environment, a process known as "maternal recognition of pregnancy". Despite being a strictly animal-only term, plants independently evolved a conceptually similar strategy: the seed habit, wherein the embryo is nourished and protected by surrounding maternal tissues. We discovered that sucrose is sufficient to trigger a fertilization-independent response in the maternal tissues of Arabidopsis ovules. Upon fertilization, the release of Polycomb-mediated repression promotes the symplastic and apoplastic flow of sucrose into the seed by modulating auxin and trehalose 6-phosphate signaling. The sucrose signal is then perceived by the TARGET OF RAPAMYCIN kinase and transduced into a gibberellin response to initiate the differentiation of the seed maternal tissues. This work revealed a zygotic-maternal interplay of hormonal and sugar signaling that drives the plant "maternal recognition of fertilization", incorporating energetic cues into developmental pathways.

plant biology↗

bioRxiv2025

Wave-like SnRK1 Activation and Tre6P-Sucrose Imbalance Shape Early Salt Stress Response in Growing Alfalfa Leaves

Alfalfa (Medicago sativa L.) is a key forage crop valued for its adaptability and nutritional quality, yet salinity significantly limits its productivity, particularly in arid regions. Understanding early stress responses is crucial for improving resilience. Salt stress impairs leaf growth and photosynthesis, triggering complex, time-dependent signaling. Sucrose non-fermenting kinase 1 (SnRK1), a central metabolic sensor, regulates metabolism and growth under stress. We investigated the dynamics of SnRK1, sucrose, and trehalose-6- phosphate (Tre6P) during leaf expansion in a salt-tolerant alfalfa cultivar. Plants were hydroponically grown and exposed to 200 mM NaCl. Stress induced transient declines in chloroplast performance (Fv/Fm, performance index). SnRK1 activity peaked within 1 hour post-treatment (hpt), likely initiating metabolic shifts. By 3 hpt, sugar metabolism shifted, with increased catabolism, TCA cycle modulation, and glucose-6-phosphate accumulation. SnRK1 and sucrose showed opposing wave-like patterns, with sucrose peaking at 1 day post-treatment (dpt) as Tre6P declined, indicating a disrupted regulatory link. A second SnRK1 peak at 3 dpt correlated with reduced leaf growth. Exogenous sucrose inhibited SnRK1, while NaCl enhanced it. This is the first report of wave-like SnRK1 activation and Tre6P-sucrose uncoupling in alfalfa, highlighting early SnRK1 activation as key to salt stress adaptation. HighlightsO_LIEarly SnRK1 activation is a key determinant of salt stress response in alfalfa, linking early biochemical shifts to downstream metabolic alteration. C_LIO_LIFirst evidence of a wave-like SnRK1 activation pattern and disruption of the Tre6P- Sucrose nexus reveals novel dynamics in alfalfas stress signaling. C_LIO_LISucrose inhibits SnRK1 activity in source leaves with or without NaCl C_LI

plant biology↗

bioRxiv2025

Pharmacological Activation of NO-Sensitive Guanylyl Cyclase Ameliorates Obesity-Induced Arterial Stiffness

ObjectiveArterial stiffness, or loss of elastic compliance in large arteries, is an independent precursor of cardiovascular disease (CVD)1 and dementia2. Akin to anti-hypertensive and lipid-lowering drugs, arterial de-stiffening therapies could be beneficial at decreasing CVD risk. We previously discovered that enhanced cytoskeletal actin polymerization in vascular smooth muscle cells (VSMCs) contributes to increased arterial stiffness3. In aortas and VSMCs, we previously found that decreased NO-sensitive guanylyl cyclase (NO-GC), the NO receptor which synthesizes cGMP, caused downregulation of cGMP-dependent protein kinase I (cGKI) and of its target vasodilator-stimulated phosphoprotein (pVASPS239), leading to increased cytoskeletal actin polymerization3. In the current study, we tested whether activating NO-GC with an NO-GC activator (cinaciguat) modulates pVASPS239 and cytoskeletal actin polymerization in VSMCs, thereby preventing obesity-induced arterial stiffness. Approach & ResultsCinaciguat administration (5 mg/kg) to high fat, high sucrose diet (HFHS)-fed mice, our established model of arterial stiffness4, (1) decreased pulse wave velocity, the in vivo index of arterial stiffness, without affecting blood pressure, (2) increased aortic pVASPS239 levels, and (3) decreased the ratio of filamentous (F) to globular (G) actin, compared to vehicle administration. In cultured VSMCs, cinaciguat (10 mol/L) increased pVASPS239 levels and decreased the F/G actin ratio at baseline and after stimulation with the cytokine tumor necrosis factor (TNF), used to mimic the inflammatory milieu of HFHS aortas. These effects were abrogated in aortas and VSMCs from mice with smooth muscle-specific cGKI deletion (cGKISMKO), while being mimicked by a cell-permeable cGMP analog (8-Br-cGMP, 1 mol/L), which also decreased VSMC stiffness in vitro. ConclusionsCollectively, our data strongly support the notion that pharmacological NO-GC activation would be beneficial in decreasing obesity-associated arterial stiffness by decreasing VSMC cytoskeletal actin hyper-polymerization. If translated to humans, NO-GC activators could become a viable approach to clinically treat arterial stiffness, which remains an unmet medical need.

pharmacology and toxicology↗

bioRxiv2024

Intercellular compartmentation of trehalose 6-phosphate metabolism in Setaria viridis leaves

Trehalose 6-phosphate (Tre6P) is a signal metabolite that links carbon metabolism with plant development. Our current understanding of Tre6P metabolism and signalling is predominantly based on studies in Arabidopsis thaliana. Some features could be adapted to the specific physiology, anatomy, and life cycle of this C3 eudicot model species, and thus might not be representative of other angiosperms. To better understand Tre6P metabolism in monocot C4 species we used Setaria viridis, which has been widely adopted as a model for the major C4 NADP-malic enzyme subtype crop species, such as maize (Zea mays), sorghum (Sorghum bicolor) and sugarcane (Saccharum officinarum). In this work, we analysed the levels of transcripts encoding Tre6P-related enzymes in different tissues and cell types from S. viridis. The TREHALOSE-6-PHOSPHATE SYNTHASE1 transcript, its encoded protein (TPS1, the enzyme responsible for Tre6P synthesis) and Tre6P were mainly located in bundle sheath cells of S. viridis. Our results show that Tre6P is predominately synthesized and located in bundle sheath and associated cells. HighlightTrehalose 6-phosphate, a sugar signalling metabolite, is mainly present in the bundle sheath cells of Setaria viridis leaves.

plant biology↗

bioRxiv2024

The stress-protectant molecule trehalose mediates fluconazole tolerance in Candida glabrata

The incidence of non-albicans Candida infections has witnessed a substantial rise in recent decades. Candida glabrata (Nakaseomyces glabratus), an opportunistic human fungal pathogen, is accountable for both superficial mucosal and life-threatening bloodstream infections, particularly in immunocompromised individuals. Distinguished by its remarkable resilience to environmental stressors, C. glabrata exhibits intrinsic tolerance to azoles and a high propensity to swiftly develop azole resistance during treatment. The molecular mechanism for the high tolerance is not fully understood. In this work we investigated the possible role of trehalose in this tolerance. We generated mutants in the C. glabrata TPS1, TPS2, and NTH1 genes, encoding trehalose 6-phosphate synthase (Tps1), trehalose 6-phosphate phosphatase (Tps2), and neutral trehalase (Nth1), respectively. As expected, the tps1{Delta} strain cannot grow on glucose. The tps2{Delta} strain demonstrated diminished trehalose accumulation and very high levels of trehalose 6-phosphate (T6P), the biosynthetic intermediate, in comparison to the WT strain. Whereas these higher T6P levels did not affect growth, the lower trehalose levels clearly resulted in lower environmental stress tolerance and a lower susceptibility to fluconazole. More interestingly, the tps2{Delta} strain completely lost tolerance to fluconazole, characterized by the absence of slow growth at supra-MIC concentrations of this drug. All these phenotypes are reversed in the nth1{Delta} strain, which accumulates high levels of trehalose. Our findings underscore the role of trehalose in enabling tolerance towards fluconazole in C. glabrata. We further show that the change in tolerance is a result of the effect that trehalose has on the sterol pattern in the cell, showing that accumulation of toxic sterols correlate with absence of tolerance. Author summaryC. glabrata is a yeast of significant medical importance, known for causing nosocomial outbreaks of invasive candidiasis. Its propensity to develop resistance to antifungal medications, notably azoles such as fluconazole, raises considerable concern. An underlying reason for the rapid development of resistance is its intrinsic tolerance to this drug. The underlying molecular mechanism of tolerance to fluconazole is heavily studied but not understood. This study sheds light on the involvement of trehalose in modulating tolerance to fluconazole. We have elucidated that trehalose serves not only as a protective agent against various stresses but also as a mediator of fluconazole resistance and tolerance. To start elucidating how this may work, we provide data that trehalose (or the enzymes affecting the amount of trehalose in the cell) alters the ergosterol type and level in the cells, thereby affecting tolerance.

microbiology↗

bioRxiv2023

Direct and indirect responses of the Arabidopsis transcriptome to an induced increase in trehalose 6-phosphate

Trehalose 6-phosphate (Tre6P) is an essential signal metabolite that reports and regulates the level of sucrose, linking growth and development to the metabolic status. We hypothesized that Tre6P plays a role in mediating the regulation of gene expression by sucrose. To test this, we performed transcriptomic profiling on Arabidopsis plants that expressed a bacterial trehalose-6-phosphate synthase (TPS) under the control of an ethanol-inducible promoter. Induction led to a 4-fold rise in Tre6P levels, a concomitant decrease in sucrose, and significant changes of over 13,000 transcripts and two-fold or larger changes of over 5000 transcripts. Comparison with nine published responses to sugar availability allowed some of these changes to be linked to the rise in Tre6P, while others were probably due to lower sucrose or other indirect effects. Changes linked to Tre6P included repression of photosynthesis and induction of many growth-related processes including ribosome biogenesis. About 500 starvation-related genes are known to be induced by SUCROSE-NON-FERMENTING-1-RELATED KINASE 1 (SnRK1). They were largely repressed by Tre6P in a manner consistent with Tre6P acting to inhibit SnRK1. SnRK1 also represses many genes that are involved in biosynthesis and growth. These responded to Tre6P in a more complex manner, pointing to Tre6P also interacting with further C-signaling pathways. In addition, elevated Tre6P modified expression of genes encoding regulatory subunits of the SnRK1 complex and TPS class II and FLZ proteins that are thought to modulate SnRK1 function, and genes involved in the circadian clock and in TOR, light, abscisic acid and other hormone signaling. One sentence summaryAn induced increase in trehalose 6-phosphate levels has direct effects on gene expression via inhibition of SUCROSE-NON-FERMENTING-1-RELATED KINASE 1 and interactions with light, circadian clock and phytohormone signaling, and widespread indirect effects on gene expression from reciprocal changes in sucrose levels.

plant biology↗

bioRxiv2023

Spliceosomal complex components are critical for adjusting the C:N balance during high-light acclimation

Plant acclimation to an ever-changing environment is decisive for growth, reproduction and survival. Light availability limits biomass production on both ends of the intensity spectrum. Therefore, the adjustment of plant metabolism is central to high-light (HL) acclimation, and accumulation of photoprotective anthocyanins is commonly observed. However, mechanisms and factors regulating the HL acclimation response are less clear. Two Arabidopsis mutants of spliceosome components exhibiting a pronounced anthocyanin overaccumulation in HL were isolated from a forward genetic screen for new factors crucial for plant acclimation. Time-resolved physiological, transcriptome and metabolome analysis revealed a vital function of the spliceosome components for rapidly adjusting gene expression and metabolism. Deficiency of INCREASED LEVEL OF POLYPLOIDY1 (ILP1), NTC-RELATED PROTEIN1 (NTR1), and PLEIOTROPIC REGULATORY LOCUS1 (PRL1) resulted in a marked overaccumulation of carbohydrates and strongly diminished amino acid biosynthesis in HL. While not generally limited in N-assimilation, ilp1, ntr1, and prl1 mutants showed higher glutamate levels and reduced amino acid biosynthesis in HL. The comprehensive analysis reveals a function of the spliceosome in the conditional regulation of the carbon:nitrogen-balance and the accumulation of anthocyanins during HL acclimation. The importance of gene expression, metabolic regulation, and re-direction of carbon towards anthocyanin biosynthesis for HL acclimation are discussed.

molecular biology↗

bioRxiv2023

S1 basic leucine zipper transcription factors shape plant architecture by controlling C/N partitioning to apical and lateral organs

Plants exhibit an immense plasticity in their architecture. While the impact of hormonal regulation is well-characterised, the importance of sugar-signalling has just recently emerged. Here, we addressed which sugar-signalling components mediate the trade-off between growth of apical versus lateral meristems and how they control organ sink-strength. Thereby, we unravelled a novel developmental function of the sugar-controlled S1 basic-leucine-zipper (S1-bZIP) transcription factors in establishing global source-sink interactions. Applying comprehensive molecular, analytical, and genetic approaches, we demonstrate that S1-bZIPs operate in a redundant manner to control tissue-specific expression of defined SWEET sugar-transporters and the GAT1_2.1 glutaminase. By these means, S1-bZIPs control carbohydrate (C)-channelling from source leaves to apical shoot and root organs and tune systemic organic nitrogen (N)-supply to restrict lateral organ formation by C/N depletion. Knowledge of the underlying mechanisms controlling plant C/N partitioning is of pivotal importance for breeding strategies to generate plants with desired architectural and nutritional characteristics.

plant biology↗

bioRxiv2023

The transcription factor bZIP11 acts antagonistically with trehalose 6-phosphate to inhibit shoot branching

The ontogenetic regulation of shoot branching allows plants to adjust their architecture in accordance with the environment. This process is due to the regulation of axillary bud outgrowth into branches, which can be induced by increasing sugar availability to the buds through decapitation of the shoot tip. Different sugar signalling components have been identified in the induction of shoot branching. However, the molecular components that maintain bud dormancy in response to sugar starvation remain largely unknown. Here, we show at the genetic level that basic leucine zipper 11 (bZIP11), a transcription factor that plays important roles in response to sugar starvation in plants, inhibits shoot branching in Arabidopsis thaliana. Physiology experiments demonstrated that bZIP11 protein levels are decreased by decapitation. Molecular and genetic evidence suggests that bZIP11 acts in a negative feedback loop with trehalose 6-phosphate (Tre6P), a sugar signal that promotes shoot branching. Our data also suggest that the central energy sensor SUCROSE NON-FERMENTING 1 RELATED KINASE1 (SnRK1), alleviates the inhibitory effect of Tre6P on bZIP11 protein accumulation and inhibits shoot branching. Altogether, these data provide a working model that involves bZIP11, Tre6P and SnRK1 in the regulation of shoot branching.

plant biology↗

bioRxiv2023

Role of the NO-GC/cGMP signaling pathway in platelet biomechanics

Cyclic guanosine monophosphate (cGMP) is a second messenger produced by the NO-sensitive guanylyl cyclase (NO-GC) enzyme. In platelets, the NO-GC/cGMP pathway inhibits aggregation. One aspect of the inhibitory mechanism involves changes in the cytoskeleton; however, the molecular mechanisms underlying platelet inhibition and its correlation with cytoskeletal cellular stiffness are poorly understood. We measured the cellular stiffness of individual platelets after treatment with the NO-GC stimulator riociguat or the NO-GC activator cinaciguat, using scanning ion conductance microscopy (SICM). We quantified changes in platelet shape using deep learning-based platelet morphometry. Cytoskeletal actin polymerization and platelet activation were measured by co-immunostaining F-actin and P-selectin, respectively. To test for clinical applicability of NO-GC stimulators in the context of increased thrombogenicity risk, we investigated the effect of riociguat on platelets from human immunodeficiency virus (HIV)-positive patients taking abacavir sulphate (ABC)-containing regimens, compared with HIV-negative volunteers. Stimulation of human and murine platelets with the NO-GC stimulator riociguat or with the NO-GC activator cinaciguat downregulated P-selectin expression, decreased F-actin polymerization, and decreased cellular stiffness by {approx}50%, compared to vehicle control. In addition, platelets became more circular, indicating decreased activation. Riociguat did not cause any change in platelet aggregation or circularity in HIV-positive patients taking ABC-containing regimens. These results corroborate a functional role of the NO-GC enzyme in platelet biomechanics (cellular stiffness) in correlation with the inhibition of platelet activation and morphological changes. The observed changes in stiffness and platelet shape therefore demonstrate the possibility of pharmacologically targeting the NO-GC/cGMP pathway.

biochemistry↗