Biology subjects

Novak, O.

Publications and source records attributed to Novak, O..

At least 37 records · Page 2Linked to original sources

bioRxiv2025

The transcription factor NO TRANSMITTING TRACT / WIP2 regulates cytokinin homeostasis in Arabidopsis

NO TRANSMITTING TRACT / WIP2 (NTT/WIP2) is a zinc finger transcription factor that alters developmental programs in Arabidopsis when overexpressed. Loss of NTT function, alone or in combination with closely related genes, leads to developmental defects in gynoecia and roots, respectively. Its overexpression phenotype resembles the effects of cytokinin treatments, suggesting a potential connection to this hormonal pathway. To further investigate this connection, we conducted cytokinin content and response evaluations, and transcriptome analyses in an inducible NTT line. Alterations in cytokinin content and response, as evaluated with the TCSn::GFP line, were observed. In both cases, as in the global expression analyses, the observed changes were dependent on the tissue analyzed. Moreover, Y1H and transactivation assays suggested direct NTT binding to the IPT5, AHP6 and CKX7, regulatory regions. We propose that NTT, among other mechanisms, regulates development through the modulation of cytokinin homeostasis at different levels, including its local concentration. Since NTT is a target of AUXIN RESPONSE FACTOR 5 / MONOPTEROS, the results presented here indicate that NTT connects an auxin input to a change in cytokinin levels.

plant biology↗

bioRxiv2025

Welcome pathogens: transient heat dampens the responses to acibenzolar-S-methyl beyond defenses in apple plants

Climate change affects plant-pathogen interactions, with disease outcome varying depending on pathosystem and environmental scenario. In Arabidopsis, a thermo-sensitive module of salicylic acid (SA) signaling makes immunity vulnerable to heat. The potent resistance inducer acibenzolar-S-methyl (ASM), an SA analogue that up-regulates transcription of defense genes, could restore plant protection under heat but not core SA signaling. Here, we investigated how high temperature rewires the ASM-induced responses of the apple immune system. We treated apple plants with ASM under contrasting heatwave scenarios and subsequently exposed them to Erwinia amylovora (the fire blight bacterium) or Venturia inaequalis (the apple scab fungus) while monitoring gene expression. While pre-exposing apple plants to high temperature did not change their susceptibility to pathogens, it drove a loss of ASM-induced protection. Transcriptomic analysis revealed broad dampening of ASM-regulation upon high temperature, for a wide range of biological processes beyond defense. We uncovered thermo-sensitive "resistance" and "susceptibility" marker genes with ASM-responsiveness being critically vulnerable to heat. We concluded that exposure to heatwave prevents ASM from fully mounting its protective responses in apple, not only lowering defenses but also offering more favorable hosting conditions. Our work highlights plant immunity as the joint outcome of resistant and susceptible responses. Summary StatementWe found that heatwaves "disarm" apples ability to mount an effective inducible-immunity response against two major diseases, fire blight and apple scab. Heatwaves not only prevent full expression of plant defenses, but also favor a physiological status that is beneficial to the pathogens.

plant biology↗

bioRxiv2025

Metabolic network divergence: polyamine and ethylene dynamics in Arabidopsis thaliana and Solanum lycopersicum

Polyamines are ubiquitously present in all living organisms. In plants, together with phytohormone ethylene, their metabolism plays a crucial role in plant stress and ontogenesis. We have evaluated differences in the responses of model plants Arabidopsis thaliana and Solanum lycopersicum to abiotic stresses and metabolic modulators based on key metabolite levels. Previous approaches have often focused separately on either polyamines, amino acids, or ethylene precursors. As these pathways are directly interconnected, their simultaneous evaluation can significantly impact our understanding of their core mechanisms. We have therefore developed a novel and validated liquid chromatography - tandem mass spectrometry based method, enabling quantification of fourteen compounds: the amino acids L-arginine, L-citrulline, L-ornithine; biogenic amines N-acetyl-L-ornithine and agmatine; the polyamines putrescine, spermidine, spermine, thermospermine, N-acetylputrescine, cadaverine, homospermidine; together with methionine and 1-aminocyclopropane-1-carboxylic acid, serving as key non-volatile precursors of ethylene. Our analysis revealed distinct metabolic responses between Arabidopsis and tomato, highlighted by species-specific differences in polyamine metabolism and ethylene precursors dynamics. Drought and salinity stresses triggered fundamentally different metabolic adjustments, with drought consistently inducing higher metabolite levels and spermine showing stress-specific responses. Metabolic inhibitor treatments with aminoguanidine and L-norvaline revealed further divergencies, mainly demonstrated as significant variations in ethylene precursor levels. For all approaches, Arabidopsis displayed more pronounced metabolic fluctuations compared to tomato. These results provide direct insights into contrasting metabolic plasticity and the interconnected roles of polyamines, amino acids, and ethylene precursors in plant responses and adaptations.

plant biology↗

bioRxiv2024

The monomer/dimer switch modulates the activity of plant adenosine kinase

HighlightThe switch from active monomers to inactive dimers in plant ADKs impacts overall enzyme activity and represents a novel negative feedback-loop mechanism to maintain steady levels of adenosine and AMP. Adenosine undergoes ATP-dependent phosphorylation catalyzed by adenosine kinase (ADK). In plants, ADK also phosphorylates cytokinin ribosides, transport forms of the hormone. Here, we investigated the substrate preferences, oligomeric states and structures of ADKs from moss (Physcomitrella patens) and maize (Zea mays) alongside metabolomic and phenotypic analyses. We showed that dexamethasone-inducible ZmADK overexpressor lines in Arabidopsis can benefit from a higher number of lateral roots and larger root areas under nitrogen starvation. We discovered that maize and moss enzymes can form dimers upon increasing protein concentration, setting them apart from the monomeric human and protozoal ADKs. Structural and kinetic analyses revealed a catalytically inactive unique dimer. Within the dimer, both active sites are mutually blocked. The activity of moss ADKs, exhibiting a higher propensity to dimerize, was tenfold lower compared to maize ADKs. Two monomeric structures in a ternary complex highlight the characteristic transition from an open to a closed state upon substrate binding. This suggests that the oligomeric state switch can modulate the activity of moss ADKs and likely other plant ADKs. Moreover, dimer association represents a novel negative feedback mechanism, helping to maintain steady levels of adenosine and AMP.

plant biology↗

bioRxiv2024

Light quantity impacts early response to cold and cold acclimation in young leaves of Arabidopsis

Plant reactions to stress vary with development stage and fitness. This study assessed the relationship between light and chilling stress in Arabidopsis acclimation. By analyzing the transcriptome and proteome responses of expanding leaves subjected to varying light intensity and cold, 2251 and 2064 early response genes and proteins were identified, respectively. Many of these represent as yet unknown part of early response to cold, illustrating development-dependent response to stress and a duality in plant adaptations. While standard light promoted photosynthetic upregulation, plastid maintenance, and increased resilience, low light triggered a unique metabolic shift, prioritizing ribosome biogenesis and lipid metabolism and attenuating expression of genes associated with plant immunity. The comparison of early response in young leaves with that in expanded ones showed striking differences, suggesting a sacrifice of expanded leaves to support young ones. Validations of selected DEGs in mutant background confirmed a role of HSP90-1, transcription factor FLZ13, and Phospholipase A1 (PLIP) in response to cold, and the PLIP family emerged as crucial in promoting acclimation and freezing stress tolerance. The findings highlight the dynamic mechanisms that enable plants to adapt to challenging environments and pave the way for the development of genetically modified crops with enhanced freezing tolerance.

plant biology↗

bioRxiv2024

Long-term high temperatures affect seed maturation and seed coat integrity in Brassica napus

Temperatures above the optimum growth threshold affect seed development, accelerating embryo development and producing seeds with ruptured seed coats. However, the underlying mechanisms of this effect remain unclear. To investigate temperature-induced seed coat rupture, we used a multidisciplinary approach combining detailed phenotyping, transcriptomics, histology, immunolabelling, cell wall profiling and nanoindentation-based mechanics of the seed coat in oilseed rape (Brassica napus). Our data reveal that high temperatures accelerate embryo growth, resulting in larger embryos without a compensatory increase in overall seed size. This rapid embryo expansion may exert elevated mechanical stress on the seed coat cells, significantly thinning the seed coat layers. Concurrently, prolonged exposure to high temperatures drives premature biochemical maturation of the seed coat, characterized by accumulation of demethylesterified pectin. Nanoindentation analysis demonstrated that these changes may have compromised the structural integrity of seed coat cell walls. Ultimately, the weakened seed coat may not withstand the internal tension imposed by the fast-growing embryo, leading to seed coat rupture and reduced seed quality. Our work on seed maturation and the mechanism of heat-induced seed coat rupture provides valuable insights for future research into breeding thermotolerant Brassica napus, crucial in the context of a changing climate. HIGHLIGHTSO_LIGrowth of Brassica napus under long-term high temperatures accelerated embryo growth and led to seed coat rupture in approximately half of the seeds. C_LIO_LIPathways linked to cell wall modification were found to be significantly differentially regulated at high temperatures, accompanied by increased pectin demethylesterification in the seed coat. C_LIO_LIA lower reduced modulus and hardness indicate that the surface of HT seeds is mechanically more compliant and softer. Together with the reduced thickness of the seed coat layers, such a seed coat, as a whole structure, is mechanically weaker and less able to resist deformation imposed by embryo growth, resulting in seed coat rupture. C_LI

plant biology↗

bioRxiv2024

Phenylacetic acid metabolism in land plants: novel pathways and metabolites

In recent years, substantial progress has been made in exploring auxin conjugation and metabolism, primarily aiming at indole-3-acetic acid (IAA). However, the metabolic regulation of another key auxin, phenylacetic acid (PAA), remains largely uncharacterized. Here, we provide a comprehensive exploration of PAA metabolism in land plants. Through LC-MS screening across multiple plant species and their organs, we identified four previously unreported endogenous PAA metabolites: phenylacetyl-leucine (PAA-Leu), phenylacetyl-phenylalanine (PAA-Phe), phenylacetyl-valine (PAA-Val), and phenylacetyl-glucose (PAA-glc). Enzyme assays, genetic evidence, crystal structures, and docking studies demonstrate that PAA and IAA share core metabolic machinery, revealing a complex regulatory network that maintains auxin homeostasis. Furthermore, our study of PAA conjugation with amino acids and glucose suggests limited compensatory mechanisms within known conjugation pathways, pointing to the existence of alternative metabolic routes in land plants. These insights advance our knowledge of auxin-specific metabolic networks and highlight the unique complexity within plant hormone regulation.

plant biology↗

bioRxiv2024

PRC2 facilitates the transition from heterotrophy to photoautotrophy during seedling emergence

Seed-to-seedling transition represents a key developmental and metabolic switch in plants. Catabolism of seed storage reserves fuels germination and early seedling emergence until photosynthesis is established. The developmental transition is controlled by Polycomb repressive complex 2 (PRC2). However, the coordination of PRC2 activity and its contribution to transcriptional reprogramming during seedling establishment is unknown. By analysing the re-distribution of H3K27me3 and changes in gene transcription in shoot and root tissues of heterotrophic and photoautotrophic seedlings, we reveal two phases of PRC2-mediated gene repression. The first phase is independent of light and photosynthesis and results in irreversible repression of the embryo maturation programme, marked by heterotrophy and biosynthesis of reserve storage molecules. The second phase is associated with the repression of metabolic pathways related to germination and early seedling emergence, and H3K27me3 deposition in this phase is sensitive to photosynthesis inhibition. We show that preventing transcription of the PRC2-repressed glyoxylate cycle gene ISOCITRATE LYASE is sufficient to drive the vegetative phase transition in PRC2-depleted plants. This underscores a key role of PRC2 repression in the coordinated metabolic and developmental switches during seedling emergence and emphasizes the close connection between metabolic and developmental identities.

plant biology↗

bioRxiv2024

The Draparnaldia genome: alternative mechanisms for multicellularity and terrestrialization in green plants

Green plants contain two algal lineages: Streptophyte algae that diverged into land plants and Chlorophyte algae that are mostly aquatic. Draparnaldia is a Chlorophyte alga morphologically resembling mosses and living in both, the aquatic and terrestrial habitats. Because of its complex morphology and terrestrial adaptations, Draparnaldia can provide new insights into the evolution of multicellularity and terrestrialization in green plants. To develop Draparnaldia into a model, we de novo sequenced its genome and transcriptomes, and profiled its phytohormone repertoire. We found that 1) Expanded gene families in Draparnaldia with respect to unicellular Chlamydomonas are linked to multicellularity and abiotic stresses. 2) Draparnaldias terrestrial adaptations are reflected at both the morphological and molecular levels. 3) Draparnaldia synthesizes most of the phytohormones used by land plants to thrive in terrestrial habitats. All of this makes Draparnaldia a powerful model to uncover and study alternative evolutionary trajectories towards multicellularity and terrestrialization in plants.

evolutionary biology↗

bioRxiv2024

Enhanced auxin signaling hub triggers root hair growth at moderate low temperature in Arabidopsis thaliana

Root hairs (RH) as a mixed tip- and non-tip growing protrusions that develop from root epidermal cells are important for nutrient and water uptake, root anchoring, and interaction with soil microorganisms. Although nutrient availability and temperature are critical interlinked factors for sustained plant growth, the molecular mechanisms underlying their sensing and downstream signaling pathways remain unclear. Here, we identified a moderate low temperature (10{degrees}C) condition that triggers a strong RH elongation response involving several molecular components of the auxin pathway. Then, we have determined that auxin biosynthesis carried out by YUCCAs/TAA1, the auxin transport conducted by PIN2/PIN4 and AUX1/PGP4, and the auxin signaling controlled by TIR1/AFB2 coupled to four specific ARFs (ARF6/ARF8 and ARF7/ARF19), are all crucial for the RH response at moderate low temperature. These results uncover the auxin pathway as one central hub under moderate low temperature in the roots to trigger RH growth. Our work highlights the importance of moderate low temperature stimulus as a complex nutritional signal from the media soil into the roots that may be fine-tuned for future biotechnological applications to enhance nutrient uptake.

plant biology↗

bioRxiv2024

Integration of multi-omics and deep phenotyping provides novel insights into multiple abiotic stress responses in potato

Potato is highly water and space efficient but susceptible to abiotic stresses such as heat, drought, or flooding, which are severely exacerbated by climate change. Understanding of crop acclimation to abiotic stress, however, remains limited. Here, we present a comprehensive molecular and physiological high-throughput profiling of potato (Solanum tuberosum, cv. Desiree) under heat, drought and waterlogging applied as single stresses or in combinations designed to mimic realistic future scenarios. Stress-responses were monitored via daily phenotyping and multi-omics analyses of leaf samples comprising transcriptomics, proteomics, metabolomics and hormonomics at several timepoints during and after stress treatments. Additionally, critical metabolites of tuber samples were analysed at the end of the stress period. Integrative analysis of multi-omics data was performed using a bioinformatic pipeline, which was established here, based on machine learning and knowledge networks. Overall, waterlogging had the most immediate and dramatic effects on potato plants, interestingly activating ABA-responses similar to drought stress. In addition, we observed distinct stress signatures at multiple molecular levels in response to heat or drought and to a combination of both. In response to all treatments, we found a downregulation of photosynthesis at different molecular levels, an accumulation of minor amino acids and diverse stress induced hormones. Our integrative multi-omics analysis provides global insights into plant stress responses, facilitating improved breeding strategies towards climate-adapted potato varieties. One Sentence SummaryIntegrated multi-omics analysis of high-throughput phenotyping in potato reveals distinct molecular signatures of acclimation to single and combined abiotic stresses related to climate change.

plant biology↗

bioRxiv2024

ESR2 orchestrates cytokinin dynamics leading to developmental reprogramming and green callus formation

Callus formation and shoot regeneration are natural plant abilities triggered by stress and damage. They are also key components of tissue culture, which for many species is crucial for gene editing, transformation, propagation, and other technologies, and their study provides valuable insights into plant development. The transcription factor ENHANCER OF SHOOT REGENERATION 2 (ESR2/DRNL/BOL/SOB) promotes green callus formation in roots and shoot regeneration when overactive, while the phythormone cytokinin plays a prominent role in both phenomena. Yet, the positive action of ESR2 on the cytokinin pathway had not been previously described. We explored the effects of ESR2 and found that cytokinin content and the expression of the cytokinin biosynthesis gene ISOPENTENYLTRANSFERASE 5 (IPT5) increase in plants where ESR2 activity is induced. ESR2 also regulates the cytokinin signaling repressor ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER 6 (AHP6), and surprisingly, the ESR2-stimulated green calli formation requires both IPT5 and AHP6. Therefore, ESR2 promotes both cytokinin biosynthesis and cytokinin signaling inhibition and requires a paradoxical combination of these two for green callus induction. This finding provides a foundation to better understand the processes involved in tissue reprogramming towards callus formation and the role of ESR2 in shoot regeneration and the development of new organs.

plant biology↗

bioRxiv2024

Identification of RACK1A as a component of the auxin-ethylene crosstalk regulating apical hook development in Arabidopsis thaliana

Apical hook development is an ideal model for studying differential growth in plants, and is controlled by complex hormonal crosstalk, with auxin and ethylene being the major players. Here, we identified a bioactive small molecule that decelerates apical hook opening in Arabidopsis thaliana. Our genetic studies suggest that this molecule enhances or maintains the auxin maximum found in the inner hook side and requires certain auxin and ethylene signaling components to modulate apical hook opening. Using biochemical approaches, we then revealed the WD40 repeat scaffold protein RECEPTOR FOR ACTIVATED C KINASE 1A (RACK1A) as a direct target of this compound. We present data in support of RACK1A playing a positive role in apical hook opening by negatively regulating the differential auxin response gradient across the hook via specific auxin and ethylene signaling mechanisms and thereby adjusting differential cell growth, an essential process for organ structure and function in plants. We have thus identified a role for RACK1A and auxin-ethylene crosstalk in negatively regulating differential cell growth to promote apical hook opening. Significance StatementDifferential growth, or the growth of cells at different rates across tissues, is essential for providing shape and structure during plant development. The apical hook is a transient structure formed by differential cell growth across the hypocotyl tip in dark-grown seedlings, which protects the underlying tissues, and which opens during seedling development. We identified a small molecule that decelerates hook opening and discovered that it targets the protein RECEPTOR FOR ACTIVATED C KINASE 1A (RACK1A). We then showed that RACK1A promotes apical hook opening at the level of crosstalk between the plant hormones auxin and ethylene, by adjusting differential cell growth. Our work paves the way to a better understanding of how plants regulate and adapt their growth during development.

plant biology↗

bioRxiv2024

Sucrose-responsive osmoregulation of plant cell size by a long non-coding RNA

The shoot of green plants is the primary site of carbon assimilation into sugars, the key source of energy and metabolic building blocks. The systemic transport of sugars is essential for plant growth and morphogenesis. Plants evolved intricate networks of molecular players to effectively orchestrate the subcellular partitioning of sugars. Dynamic distribution of these osmotically active compounds is a handy tool to regulate cell turgor pressure. Pressure-induced mechanical forces play an instructive role in developmental biology across kingdoms. Here, we functionally characterized a long non-coding RNA, CARMA, as a negative regulator of a receptor-like kinase, CANAR. Sugar-responsive CARMA specifically fine-tunes CANAR expression in the phloem, the route of sugar transport. By controlling sugar distribution, the CARMA-CANAR module allows cells to flexibly adapt to the external osmolality and adjust the size of vascular cell types during organ growth and development. We identify a nexus of plant vascular tissue formation with cell internal pressure monitoring and reveal a novel functional aspect of long non-coding RNAs in developmental biology.

plant biology↗

bioRxiv2023

The dimorphic diaspore model Aethionema arabicum (Brassicaceae): Distinct molecular and morphological control of responses to parental and germination temperatures

Plants in habitats with unpredictable conditions are often characterized by diversifying their bet-hedging strategies that ensure fitness over a wider range of variable environmental factors. A striking example is the diaspore (seed and fruit) heteromorphism that evolved to maximize species survival in Aethionema arabicum (Brassicaceae) in which external and endogenous triggers allow the production of two distinct diaspores on the same plant. Using this dimorphic diaspore model, we identified contrasting molecular, biophysical, and ecophysiological mechanisms in the germination responses to different temperatures of the mucilaginous seeds (M+ seed morphs), the dispersed indehiscent fruits (IND fruit morphs), and the bare non-mucilaginous M- seeds obtained by pericarp (fruit coat) removal from IND fruits. Large-scale comparative transcriptome and hormone analyses of M+ seeds, IND fruits, and M- seeds provided comprehensive datasets for their distinct thermal responses. Morph-specific differences in co-expressed gene modules in seeds, as well as seed and pericarp hormone contents identified a role of the IND pericarp in imposing coat dormancy by generating hypoxia affecting ABA sensitivity. This involved expression of morph-specific transcription factors, hypoxia response and cell wall-remodeling genes, as well as altered abscisic acid (ABA) metabolism, transport, and signaling. Parental temperature affected ABA contents and ABA-related gene expression and altered IND pericarp biomechanical properties. Elucidating the molecular framework underlying the diaspore heteromorphism can provide insight into developmental responses to globally changing temperatures. IN A NUTSHELL BackgroundHeteromorphic diaspores (fruits and seeds) are an adaptive bet-hedging strategy to ensure survival in spatiotemporally variable environments. The stone cress Aethionema arabicum, an annual plant native to semi-arid habitats in Anatolia (Turkey), one of the worlds hotspots of biodiversity. It is a close relative of Arabidopsis, rapeseed, cabbage and other Brassica crops, but in contrast to these Ae. arabicum disperses two distinct diaspores from the same plant. These dimorphic diaspores are the mucilaginous seeds (dispersed by pod shatter) and indehiscent fruits (dispersed by abscission). The wing-like pericarp (fruit coat) of the single-seeded indehiscent fruit allows wind dispersal over large distances. The amounts and ratios of the dimorphic diaspores are variable and depend on the environmental conditions. The dimorphic diaspores differ in morphology, dormancy and germination properties and thereby make Ae. arabicum an excellent model for the comparative investigation of the underpinning molecular mechanisms. QuestionWe asked how temperature during fruit and seed formation and during seed germination affect dormancy release and germination speed, and how the morphology, hormonal regulation, and the expression of genes differ between the dimorphic diaspores. FindingsLarge-scale comparative transcriptome and hormone analyses of the mucilaginous seeds and the indehiscent fruits, as well as the seeds artificially extracted from indehiscent fruits by pericarp (fruit coat) removal, provided comprehensive datasets for their distinct thermal responses. Material obtained from plants grown at different temperatures during reproduction was imbibed at different temperatures for germination. This altered the abscisic acid (ABA) metabolism and the pericarp biomechanical properties. Diaspore-specific differences in response to distinct imbibition temperatures identified distinct gene expression patterns in seeds, distinct seed and pericarp hormone contents, and a role of the pericarp in generating hypoxia inside the fruit and imposing coat dormancy. This revealed distinct combinations of specific transcription factors, hypoxia responses and cell wall-remodeling genes, as well as altered signaling pathway genes. Next stepsOur large-scale comparative transcriptome datasets are easily and publicly accessible via the Aethionema arabicum web portal (https://plantcode.cup.uni-freiburg.de/aetar_db/index.php). We plan to expand this by future work on seedlings derived from the dimorphic diaspores, by comparing different Ae. arabicum genotypes, and by studying responses to specific stresses. Understanding the molecular basis of this fascinating example of developmental diversity and plasticity and its regulation by temperature is expected to add insight how plants respond to changing environmental conditions.

plant biology↗

bioRxiv2023

Cell wall integrity modulates a PHYTOCHROME-INTERACTING FACTOR (PIF) - HOOKLESS1 (HLS1) signalling module controlling apical hook formation in Arabidopsis.

Etiolated seedlings of dicots form an apical hook to protect the meristems during soil emergence. Hook formation is the result of differential growth on both sides of the hypocotyl apex and is tightly controlled by environmental cues and hormones, among which auxin and gibberellins (GAs) are the main contributors. Cell expansion is tightly regulated by the cell wall, but whether and how feedback from this structure contributes to hook development is still unclear. Here we show that etiolated seedlings of the Arabidopsis thaliana quasimodo2-1 (qua2) mutant, defective in pectin biosynthesis, display severe defects in apical hook formation and maintenance, accompanied by loss of asymmetric auxin maxima and differential cell expansion. Moreover, qua2 seedlings show reduced expression of HOOKLESS1 (HLS1) and PHYTOCHROME-INTERACTING FACTOR 4 and 5 (PIF4/5), positive regulators of hook formation, and accumulate reduced levels of the active gibberellin GA4. Treatment of wild-type seedlings with the cellulose inhibitor isoxaben (isx) also prevents hook development and represses HLS1 expression and PIF4 accumulation. Moreover, isx stabilizes the DELLA protein REPRESSOR OF ga1-3 (RGA), which inhibits HLS1 expression and hook formation. Exogenous GAs or HLS1 overexpression partially restore hook development in isx-treated seedlings. Notably, agar concentration in the medium restores, both in qua2 and isx-treated seedlings, hook development and WT-like levels of PIFs and HLS1. We propose that turgor-dependent signals link changes in cell wall integrity to the PIF4/5-HLS1 signalling module to repress differential cell elongation during hook formation. Significance statementCell wall integrity modulates apical hook development through poorly understood mechanisms. We show here that, in Arabidopsis, repression of hook formation by either mutations in pectin biosynthesis or by isoxaben treatment is at least partially mediated by the downregulation of a gibberellin-controlled signalling module that comprises PIF4/5 and HLS1. Our results indicate that the signals derived from changes in the cell wall can modulate hormone-mediated pathways to control asymmetric growth during plant development.

plant biology↗

bioRxiv2023

Cytokinins control secondary cell wall formation in the inflorescence stem of Arabidopsis

Spatiotemporal control over developmental programs is vital to all organisms. Here we show that cytokinin (signaling) deficiency leads to early secondary cell wall (SCW) formation in Arabidopsis inflorescence stem that associates with precocious upregulation of a SCW transcriptional cascade controlled by NAC TFs (NSTs). We demonstrate that cytokinin signaling through the AHK2/3 and the ARR1/10/12 suppresses the expression of several NSTs and SCW formation in the apical portions of stems. Exogenous cytokinin application reconstituted both proper development and apical-basal gradient of NST1 and NST3 in a cytokinin biosynthesis-deficient mutant. We show that AHK2 and AHK3 required functional NST1 or NST3 to control SCW initiation in the interfascicular fibers, further evidencing that cytokinins act upstream of NSTs transcription factors. The premature onset of a rigid SCW biosynthesis and altered expression of NST1/3 and VND6/7 due to cytokinin deficiency led to the formation of smaller tracheary elements (TEs) and impaired hydraulic conductivity. We conclude that cytokinins downregulate NSTs to inhibit premature SCW formation in the apical part of the inflorescence stem, facilitating thus the development of fully functional TEs and interfascicular fibers. Summary statementCytokinins attenuate premature secondary cell wall (SCW) formation via downregulating the expression of NAC TFs, the master switches of SCW transcriptional cascade, thus affecting the tracheary elements size and conductivity.

plant biology↗

bioRxiv2023

Conjugation of cis-OPDA with amino acids is a conserved pathway affecting cis-OPDA homeostasis upon stress responses

Jasmonates (JAs) are a family of oxylipin phytohormones regulating plant development and growth and mediating defense versus growth responses. The upstream JA biosynthetic precursor cis-(+)-12-oxo-phytodienoic acid (cis-OPDA) has been reported to act independently of the COI1-mediated JA signaling in several stress-induced and developmental processes. However, its means of perception and metabolism are only partially understood. Furthermore, cis-OPDA, but not JA, occurs in non-vascular plant species, such as bryophytes, exhibiting specific functions in defense and development. A few years ago, a low abundant isoleucine analog of the biologically active JA-Ile, OPDA-Ile, was detected in wounded leaves of flowering plants, opening up to the possibility that conjugation of cis-OPDA to amino acids might be a relevant mechanism for cis-OPDA regulation. Here, we extended the analysis of amino acid conjugates of cis-OPDA and identified naturally occurring OPDA-Val, OPDA-Phe, OPDA-Ala, OPDA-Glu, and OPDA-Asp in response to biotic and abiotic stress in Arabidopsis. The newly identified OPDA-amino acid conjugates show cis-OPDA-related plant responses in a JAR1-dependent manner. We also discovered that the synthesis and hydrolysis of cis-OPDA amino acid conjugates are regulated by members of the amidosynthetase GH3 and the amidohydrolase ILR1/ILL families. Finally, we found that the cis-OPDA conjugative pathway already functions in non-vascular plants and gymnosperms. Thus, one level of regulation by which plants modulate cis-OPDA homeostasis is the synthesis and hydrolysis of OPDA-amino acid conjugates, which temporarily store cis-OPDA in stress responses.

plant biology↗