Biology subjects

Kohlen, W.

Publications and source records attributed to Kohlen, W..

14 recordsLinked to original sources

bioRxiv2026

Spatiotemporal dynamics of ethylene biosynthesis shape infection and nodule initiation in Medicago truncatula

Ethylene is a well-established negative regulator of nodulation, yet how ethylene biosynthesis and perception are spatially coordinated during early symbiotic signalling remains unresolved. Here, we investigate the dynamics of ethylene responses in Medicago truncatula using transcriptomics, promoter-reporter analyses, loss-of-function approaches and a synthetic reporter. We show that the activity of the ethylene-responsive EBSn reporter shifts from inner root tissues under non-symbiotic conditions to the outer cortex and epidermis following rhizobial inoculation, revealing a spatial reprogramming of ethylene signalling. Among the eight Medicago 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHASE (ACS) genes, upon rhizobia application MtACS3 is induced in outer root cell layers, while MtACS10 is repressed in the inner cortex and pericycle, mirroring the shift in ethylene perception. Functional analysis demonstrates that MtACS10 restricts nodule initiation, whereas MtACS3 modulates infection thread number, prevents nodule clustering, and contributes to radial positioning of nodule primordia. Rhizobial induced ectopic ACS expression in the root interior counteracts MtACS10 repression and blocks nodulation, highlighting the requirement for spatially confined downregulation of ethylene biosynthesis. Together, these findings establish a framework in which localized shift in ethylene biosynthesis, mediated by distinct Medicago ACS genes, balances infection and organogenesis while co-defining the spatial limits of the root susceptible zone.

plant biology↗

bioRxiv2024

C-terminally encoded peptides promoting root symbiotic nodulation in legume plants also promote the root arbuscular mycorrhizal symbiotic interaction

C-terminally encoded peptides (CEPs) are small secreted signalling peptides that promote in legumes the root nitrogen-fixing nodulation symbiosis depending on soil mineral nitrogen availability1. In Medicago truncatula, their action is mediated by the Leucine-rich repeat receptor-like protein kinase COMPACT ROOT ARCHITECTURE 2 (CRA2)2-4. As most land plants, under inorganic phosphate (Pi) limitation, M. truncatula establishes another root endosymbiotic interaction with arbuscular fungi, the arbuscular mycorrhizal symbiosis (AMS). Because this interaction is beneficial for the plant but has a high energetic cost, it is tightly controlled by host plants to limit AMS infections mainly depending on Pi availability5. We show in this study that the expression of a subset of CEP encoding genes is enhanced in the low Pi conditions that favour AMS colonization, and that overexpression of the low Pi-induced MtCEP1 gene, previously shown to promote the nitrogen-fixing root nodulation symbiosis, enhances the AMS colonization from the initial entry point of the fungi. Conversely, a loss-of-function mutation of the CRA2 receptor required for mediating CEP peptides action2 decreases the AMS interaction capacity from the same initial fungal entry stage. Transcriptomic analyses revealed that the cra2 mutant is negatively affected in the regulation of key Pi transport and response genes as well as in the biosynthesis of strigolactone (SL) hormones that are required for establishing the AMS interaction. Accordingly, SL contents were drastically decreased in cra2 mutant roots. Overall, we showed that the CEP/CRA2 pathway promotes, in legume plants, both root nodulation and AMS depending on soil mineral nutrients availability. In briefThe establishment and maintenance of root nodule and arbuscular mycorrhizal symbioses (AMS) in legume plants is tightly regulated respectively by nitrogen and phosphate availability. Pedinotti and Teyssendier de la Serve et al. show that the CEP/CRA2 pathway, previously known to promote root competence to nodulate under low nitrogen conditions, also enhances AMS establishment by controlling the expression of Pi homeostasis and strigolactone (SL) hormone biosynthesis genes, as well as SL accumulation. HighlightsO_LIA subset of M. truncatula CEP genes is induced by AMS-promoting low phosphate conditions. C_LIO_LIThe CEP1 peptides positively regulate AMS establishment, while the cra2 CEP receptor loss of function mutants display a reduced AMS colonization. C_LIO_LIThe CEP/CRA2-dependent regulation of AMS acts through downstream signals distinct from the ones involved in root nodule symbiosis regulation. The CEP/CRA2 pathway regulates AMS establishment by controlling Pi homeostasis and strigolactone (SL) hormone biosynthesis genes, as well as SL accumulation. C_LI

plant biology↗

bioRxiv2024

Brassinosteroid and gibberellin signaling are required for Tomato internode elongation in response to low red: far-red light

In this study, we explore the dynamic interplay between the plant hormones gibberellins (GA), brassinosteroids (BR), and Indole-3-Acetic Acid (IAA) in their collective impact on plant shade avoidance elongation under varying light conditions. We focus particularly on low Red: Far-red (R:FR) light conditions achieved by supplementing the background light with FR. Our research delves into how these hormones individually and synergistically influence stem elongation in tomato plants. Through meticulous experimental modulations of GA, IAA, and BR, we demonstrate that GA and BR are sufficient but also necessary for inducing stem elongation under low R:FR light conditions. Intriguingly, while IAA alone shows limited effects, its combination with GA yields significant elongation, suggesting a nuanced hormonal balance. Furthermore, we unveil the complex interplay of these hormones under light with low R:FR, where the suppression of one hormones effect can be compensated by the others. This study provides insights into the hormonal mechanisms governing plant adaptation to light, highlighting the intricate and adaptable nature of plant growth responses. Our findings have far-reaching implications for agricultural practices, offering potential strategies for optimizing plant growth and productivity in various lighting environments. HighlightThis study unveils the interplay of brassinosteroids and gibberellins in shade avoidance elongation, revealing how tomatoes acclimate in response to far-red enriched light conditions.

plant biology↗

bioRxiv2023

Nodule organogenesis in Medicago truncatula requires local stage-specific auxin biosynthesis and transport

The importance of auxin in plant organ development including root nodule formation is well established. Using auxin reporter constructs the spatiotemporal auxin distribution pattern during nodule development has previously been illustrated. However, our understanding of how this pattern is built-up and maintained still remains elusive. To this end, we studied how the auxin gradient visualized by DR5 expression patterns at different stages of nodule development in Medicago truncatula (Medicago), is correlated with the spatiotemporal expression patterns of known auxin biosynthesis and auxin transport genes. In addition, we record the MtPIN10-GFP expression pattern and polar positioning on the cell plasma membranes during nodule primordium development to investigate the auxin flux. RNA interference and the application of auxin synthesis blockers were used to demonstrate the relevance of biosynthesis and transport at the initial stages of the nodulation process. Our results show that upon rhizobium inoculation, preceding the first mitotic activity, a specific set of MtYUCs and MtPINs as well as MtLAX2 are expressed in the pericycle contributing to the creation of an auxin maximum. Overall, we demonstrate that dynamic spatiotemporal expression of both, MtYUCs and MtPINs, result in specific auxin outputs in subsequent stages of nodule primordia and nodule meristem formation.

plant biology↗

bioRxiv2023

CYP79B2 and CYP79B3 contribute to root branching through production of the auxin precursor indole-3-acetonitrile

Lateral root placement, outgrowth and density are influenced by environmental changes, including salinity stress. CYP79B2 and B3 are two cytochrome P450 enzymes previously identified as required for root architecture remodeling in salt. They produce iAOx, a metabolite that can be converted into indole glucosinolates (IGs), camalexin and indole-3-acetic acid (IAA), a type of auxin. We report here that lateral root appearance, induced by an auxin maximum in the bending zone after gravistimulation, is delayed in the absence of CYP79B2/B3. This delay traces back to a decrease in early lateral root growth after emergence, taking place before lateral roots are macroscopically visible. We measured gene transcripts and abundance of metabolites in the iAOx pathway in root segments that are forming lateral roots. Genes involved in tryptophane and IG biosynthesis were upregulated in cyp79b2/b3 mutants, suggesting a transcriptional feedback-loop. Salt stress was found to increase the expression of genes involved in IAN biosynthesis, a precursor of both IAA and camalexin, in the root during lateral root formation. Moreover, salt increases the concentration of IAN in tissue forming lateral roots in a CYP79B2/B3 dependent manner, but these changes in IAN did not coincide with altered IAA levels. Both the reduction in lateral root density under salt and the delayed lateral root appearance in cyp79b2/b3 knock-out mutants can be complemented by exogenous application of IAN. Our results reveal a role for the iAOx pathway in regulating the timing of lateral root appearance, allowing the modulation of lateral root density under salt stress.

plant biology↗

bioRxiv2023

Comparative Phylogenomics and Phylotranscriptomics Provide Insights into the Genetic Complexity of Nitrogen Fixing Root Nodule Symbiosis

Plant root nodule symbiosis (RNS) with mutualistic nitrogen-fixing bacteria is restricted to a single clade of angiosperms, the Nitrogen-Fixing Nodulation Clade (NFNC), and is best understood in the legume family. It is widely accepted that nodulation originated through the assembly of modules recruited from existing functions, such as mycorrhizal symbiosis, polar growth, and lateral root development. Because nodulating species are scattered within the NFNC, the number of times nodulation has evolved or has been lost has been a matter of considerable speculation. This interesting evolutionary question has practical implications concerning the ease with which nodulation might be engineered in non-nodulating crop plants. Nodulating species share many commonalities, due either to divergence from a common ancestor over 100 million years ago or to convergence or deep homology following independent origins over that same time period. In either case, comparative analyses of diverse nodulation syndromes can provide insights into constraints on nodulation--what must be acquired or cannot be lost for a functional symbiosis--and what the latitude is for variation in the symbiosis. However, much remains to be learned about nodulation, especially outside of legumes. Here we present new information across the spectrum of nodulating groups. We find no evidence for convergence at the level of amino acid residues or gene family expansion across the NFNC. Our phylogenomic analyses further emphasize the uniqueness of the transcription factor, NIN, as a master regulator of nodulation, and identify key mutations affecting its function across the NFNC. We find that nodulation genes are over-represented among orthologous gene groups (OGs) present in the NFNC common ancestor, but that lineage-specific OGs play major roles in nodulation. We identified over 900,000 conserved noncoding elements (CNEs), of which over 300,000 were unique to NFNC species. A significant proportion of these are associated with nodulation-related genes and thus are candidates for transcriptional regulators.

evolutionary biology↗

bioRxiv2022

Cytokinin synthesis and export from symbiotic root nodules coordinates shoot growth with nitrogen fixation

O_LIDevelopment of symbiotic root nodules is a cytokinin-dependent process that is critical to nitrogen acquisition in legumes. The extent and manner in which root nodules contribute to whole-plant cytokinin and nitrogen supply signalling is unknown. C_LIO_LIUsing a combination of genetic, biochemical and physiological approaches, we characterised the role of cytokinin synthesis, export and perception in coordination of symbiotic nodule development and shoot growth in the legume Lotus japonicus. C_LIO_LILjPup1 encodes a plasma membrane localised cytokinin exporter with isopentenyladenine (iP) and trans-Zeatin (tZ) export capacity. LjPup1 shows a distinct nodule-specific expression pattern with greatest transcript levels detected in mature nodules. Mutants accumulate more isopentenyladenine riboside (iPR) in nodule tissues and demonstrate hallmarks of reduced cytokinin signalling. Despite normal nodule numbers and function, shoot growth is markedly reduced in Ljpup1 mutants, as well as in mutants impaired in tZ biosynthesis. C_LIO_LIWe found symbiotic root nodules contribute to shoot growth via export of active cytokinins. A cytokinin exporter in the purine permease family thus contributes to long-distance cytokinin homeostasis regulating plant development. C_LI

plant biology↗

bioRxiv2022

Selective degradation of ARF monomers controls auxin response in Marchantia

The plant signaling molecule auxin controls a variety of growth and developmental processes in land plants. Auxin regulates gene expression through a nuclear auxin signaling pathway (NAP) consisting of a ubiquitin ligase auxin receptor TIR1/AFB, its Aux/IAA degradation substrate, and the DNA-binding ARF transcription factors. While extensive qualitative understanding of the pathway and its interactions has been obtained by studying the flowering plant Arabidopsis thaliana, it is so far unknown how these translate to quantitative system behaviour in vivo, a problem that is confounded by large NAP gene families in this species. Here we used the minimal NAP of the liverwort Marchantia polymorpha to quantitatively map NAP protein accumulation and dynamics in vivo through the use of knock-in fluorescent fusion proteins. Beyond revealing the native accumulation profile of the entire NAP protein network, we discovered that the two central ARFs MpARF1 and MpARF2 are proteasomally degraded. This degradation serves two functions: it tunes the stoichiometry of auxin-responsive, positively acting MpARF1 and auxin-independent, negatively acting MpARF2, thereby permitting auxin response. Secondly, through mapping a minimal degradation motif, we found that degradation is likely selective for MpARF2 monomers and favours accumulation of dimers. Interfering with MpARF1:MpARF2 stoichiometry or preventing degradation of MpARF2 monomers caused strong growth defects associated with auxin response defects. Thus, quantitative analysis of the entire Marchantia NAP, allowed to identify a novel regulatory mechanism in auxin response, built on regulated ARF degradation.

plant biology↗

bioRxiv2022

Long-lasting impact of chito-oligosaccharide application on strigolactone biosynthesis and fungal accommodation promotes arbuscular mycorrhiza in Medicago truncatula

O_LIThe establishment of arbuscular mycorrhiza (AM) between plants and Glomeromycotina fungi is preceded by the exchange of chemical signals: fungal released Myc-factors, including chitoligosaccharides (CO) and lipo-chitooligosaccharides (LCO), activate plant symbiotic responses, while root exuded strigolactones stimulate hyphal branching and boost CO release. C_LIO_LIFurthermore, fungal signaling reinforcement through CO application was shown to promote AM development in Medicago truncatula, but the cellular and molecular bases of this effect remained unclear. C_LIO_LIHere we focused on long-term M. truncatula responses to CO treatment, demonstrating its impact on the transcriptome of both mycorrhizal and non-mycorrhizal roots over several weeks and providing a novel insight into the mechanistic bases of the CO-dependent promotion of AM colonization. C_LIO_LICO treatment caused the long-lasting regulation of strigolactone biosynthesis and fungal accommodation related genes. This was mirrored by an increase in root didehydro-orobanchol content, and the promotion of accommodation responses to AM fungi in root epidermal cells. Lastly, an advanced down-regulation of AM symbiosis marker genes was observed at the latest time point in CO-treated plants, in line with an increased number of senescent arbuscules. C_LIO_LIOverall, CO treatment triggered molecular, metabolic and cellular responses underpinning a protracted acceleration of AM development. C_LI

plant biology↗

bioRxiv2022

Local light signalling at the leaf tip drives remote differential petiole growth through auxin-gibberellin dynamics

Although plants are immobile, many of their organs are flexible to move in response to environmental cues. In dense vegetation plants detect neighbours through far-red light perception with their leaf tip. They respond remotely, with asymmetrical growth between the abaxial and adaxial sides of the leafstalk, the petiole. This results in upward movement that brings the leaf blades into better lit zones of the canopy. The plant hormone auxin is required for this response, but it is not understood how non-differential leaf tip-derived auxin can remotely regulate movement. Here we show that remote light signalling promotes auxin accumulation in the abaxial petiole by reinforcing an intrinsic auxin transport directionality. In the petiole, auxin elicits a response of both auxin as well as a second growth promoter; gibberellin. We show that this dual regulation is necessary for hyponastic leaf movement in response to light. Our results reveal how plants can spatially relay information about neighbour proximity from their sensory leaf tips to the petiole base, thus driving adaptive growth.

plant biology↗

bioRxiv2021

Medicago SPX1 and SPX3 regulate phosphate homeostasis, mycorrhizal colonization and arbuscule degradation

To acquire sufficient mineral nutrients such as phosphate (Pi) from the soil, most plants engage in a symbiosis with arbuscular mycorrhizal (AM) fungi. Attracted by plant-secreted strigolactones, the fungi colonize the roots and form highly-branched hyphal structures called arbuscules inside inner cortex cells. It is essential that the host plant controls the different steps of this interaction to maintain its symbiotic nature. However, how plants sense the amount of Pi obtained from the fungus and how this determines the arbuscule lifetime is far from understood. Here, we show that Medicago truncatula SPX-domain containing proteins SPX1 and SPX3 regulate root phosphate starvation responses as well as fungal colonization and arbuscule degradation. SPX1 and SPX3 are induced upon phosphate starvation but become restricted to arbuscule-containing cells upon establishment of the symbiosis. Under Pi-limiting conditions they facilitate the expression of the strigolactone biosynthesis gene DWARF27, which correlates with increased fungal branching by root exudates and increased root colonization. Later, in the arbuscule-containing cells SPX1 and SPX3 redundantly control the timely degradation of arbuscules. This regulation does not seem to involve direct interactions with known transcriptional regulators of arbuscule degradation. We propose a model where SPX1 and SPX3 control arbuscule degeneration in a Pi-dependent manner via a yet-to-identify negative regulator.

plant biology↗

bioRxiv2020

Nitrate inhibits nodule organogenesis through inhibition of cytokinin biosynthesis in Lotus japonicus

Legumes balance nitrogen acquisition from soil nitrate with symbiotic nitrogen fixation. Nitrogen fixation requires establishment of a new organ, which is a cytokinin dependent developmental process in the root. We found cytokinin biosynthesis is a central integrator, balancing nitrate signalling with symbiotic acquired nitrogen. Low nitrate conditions provide a permissive state for induction of cytokinin by symbiotic signalling and thus nodule development. In contrast, high nitrate is inhibitory to cytokinin accumulation and nodule establishment in the root zone susceptible to nodule formation. This reduction of symbiotic cytokinin accumulation was further exacerbated in cytokinin biosynthesis mutants, which display hypersensitivity to nitrate inhibition of nodule development, maturation and nitrogen fixation. Consistent with this, cytokinin application can rescue nodulation and nitrogen fixation of biosynthesis mutants in a concentration dependent manner. These inhibitory impacts of nitrate on symbiosis occur in a Nlp1 and Nlp4 dependent manner and contrast with the positive influence of nitrate on cytokinin biosynthesis that occurs in non-symbiotic species. Altogether this shows that legumes, as exemplified by Lotus japonicus, have evolved a different cytokinin response to nitrate compared to non-legumes. One sentence summaryCytokinin biosynthesis is suppressed by nitrate in Lotus japonicus, providing a mechanism for nitrate inhibition of symbiotic nodule organogenesis.

plant biology↗

bioRxiv2018

Nitrate inhibition of nodule formation in Medicago truncatula is mediated by ACC SYNTHASE 10

Legumes form a mutualistic endosymbiosis with nitrogen-fixing rhizobia. These rhizobia are housed intracellularly in specialised lateral root organs, called nodules. Initiation of these nodules is triggered by bacterial derived signalling molecules, lipochitooligosaccharides (LCO). The process of nitrogen fixation is highly energy-demanding and therefore nodule initiation is tightly regulated. Nitrate is a potent inhibitor of nodulation. However, the precise mechanisms by which nitrate inhibits nodulation is poorly understood. Here, we demonstrate that in Medicago truncatula nitrate interferes with the transcriptional regulation of the ethylene biosynthesis gene ACC SYNTHASE 10. ACSs commit the rate limiting step in ethylene biosynthesis and in M. truncatula ACS10 is highly expressed in the zone of the root where nodulation occurs. Our results show that a reduction in ACS10 expression in response to LCO exposure correlates with the ability to form nodules. In addition, RNAi-mediated knockdown of ACS10 confers nodulation ability under otherwise inhibitory nitrate conditions. This discovery sheds new light on how ethylene is involved in the inhibition of nodulation by nitrate, bringing us one step closer to understanding how plants regulate their susceptibility towards rhizobia.

plant biology↗

bioRxiv2017

Parallel loss of symbiosis genes in relatives of nitrogen-fixing non-legume Parasponia

Rhizobium nitrogen-fixing nodules are a well-known trait of legumes, but nodules also occur in other plant lineages either with rhizobium or the actinomycete Frankia as microsymbiont. The widely accepted hypothesis is that nodulation evolved independently multiple times, with only a few losses. However, insight in the evolutionary trajectory of nodulation is lacking. We conducted comparative studies using Parasponia (Cannabaceae), the only non-legume able to establish nitrogen fixing nodules with rhizobium. This revealed that Parasponia and legumes utilize a large set of orthologous symbiosis genes. Comparing genomes of Parasponia and its non-nodulating relative Trema did not reveal specific gene duplications that could explain a recent gain of nodulation in Parasponia. Rather, Trema and other non-nodulating species in the Order Rosales show evidence of pseudogenization or loss of key symbiosis genes. This demonstrates that these species have lost the potential to nodulate. This finding challenges a long-standing hypothesis on evolution of nitrogen-fixing symbioses, and has profound implications for translational approaches aimed at engineering nitrogen-fixing nodules in crop plants.

plant biology↗