Biology subjects

Stepanova, A. N.

Publications and source records attributed to Stepanova, A. N..

10 recordsLinked to original sources

bioRxiv2026

An Integrated Spatially Resolved Mechanistic Model of Hierarchical Auxin-Cytokinin-Ethylene Crosstalk Underlying Root Growth Inhibition in Arabidopsis

Decoding how plants integrate multiple hormone signals to coordinate growth requires tools capable of resolving pathway interactions at cellular resolution in living tissue. Here we present ACE (Auxin-Cytokinin-Ethylene) and ACE2, proof-of-concept single-locus reporters to simultaneously capture activity of multiple hormones. Deploying ACE alongside well-established reporters, exogenous hormone treatments, and reverse-genetic perturbations of hormone biosynthesis, signaling, and transport in three-day-old etiolated Arabidopsis seedlings, we dissect the spatiotemporal hierarchy governing primary root elongation and root apical meristem (RAM) size. We demonstrate that both ethylene- and cytokinin-triggered root growth inhibition involve a boost of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 (TAA1)-mediated auxin biosynthesis and AUXIN RESISTANT1 (AUX1)-dependent auxin redistribution. Two spatially distinct auxin responses underlie the respective root growth effects: ethylene expands TAA1-dependent auxin biosynthesis from the root vasculature into the epidermis and promotes AUX1-mediated auxin import into the transition and elongation zones to inhibit cell elongation, while cytokinin confines ethylene-dependent TAA1-boosted activity to the vasculature and drives auxin accumulation in lateral root cap cells to reduce RAM size. Together, these data establish a reciprocal regulatory loop between these hormones, positioning ethylene as a convergence node in auxin-cytokinin crosstalk, and cytokinin as a modulator of the ethylene-auxin interaction. Critically, the changes in cross-activated reporter patterns described for different genetic backgrounds, alongside quantitative assessment of hormone-specific inhibition of the mutants growth, were consistent with the multi-hormone network established over two decades of research, and added cell-type-resolved spatial detail and a proposed hierarchy for the etiolated seedling root. Finally, a second-generation reporter, ACE2, overcomes key technical limitations of ACE, expanding the platforms capacity toward a higher-order multi-hormone monitoring system. These resources expand the Arabidopsis genetic toolkit and provide a generalizable framework instrumental for dissecting multi-hormone signaling hierarchies at the cellular level.

plant biology↗

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↗

bioRxiv2025

The CYP71A, NIT, AMI, and IAMH gene families are dispensable for indole-3-acetaldoxime-mediated auxin biosynthesis in Arabidopsis

Indole-3-acetic acid (IAA) is a crucial auxin governing plant development and environmental responses. While the indole-3-pyruvic acid (IPyA) pathway is the predominant IAA biosynthesis route, other pathways, like the indole-3-acetaldoxime (IAOx) pathway, have been proposed. The IAOx pathway has garnered attention due to its supposed activation in auxin-overproducing mutants (e.g., sur1, sur2, ugt74b1) and the auxin-like responses triggered by exogenous application of its proposed intermediates: IAOx, indole-3-acetonitrile (IAN), and indole-3-acetamide (IAM). However, despite supporting evidence for individual steps, conclusive physiological relevance of the IAOx pathway remains unproven. Using a comprehensive genetic approach combined with metabolic and phenotypic profiling, we demonstrate that mutating gene families proposed to function in the IAOx pathway does not result in prominent auxin-deficient phenotypes, nor are these genes required for high-auxin production in the sur2 mutant. Our findings also challenge the previously postulated linear IAOx pathway. While exogenously provided IAOx, IAN, and IAM can be converted to IAA in vivo, they do not act as precursors for each other. Finally, our findings question the physiological relevance of IAM and IAN as IAA precursors in plants and suggest the existence of a yet uncharacterized auxin biosynthetic route, likely involving IAOx as an intermediate, for the production of IAA in the sur2 mutant. Future identification of the metabolic steps and the corresponding genes in this new pathway may uncover the previously unknown way of synthesizing IAA in plants.

genetics↗

bioRxiv2025

EBSn, a robust synthetic reporter for monitoring ethylene responses in plants

Ethylene is a gaseous plant hormone that controls a wide array of physiologically relevant processes, including plant responses to biotic and abiotic stress, and induces ripening in climacteric fruits. To monitor ethylene in plants, analytical methods, phenotypic assays, gene expression analysis, and transcriptional or translational reporters are typically employed. In the model plant Arabidopsis, two ethylene-sensitive synthetic transcriptional reporters have been described, 5xEBS:GUS and 10x2EBS-S10:GUS. These reporters harbor a different type, arrangement, and number of homotypic cis-elements in their promoters and thus may recruit the ethylene master regulator EIN3 in the context of alternative transcriptional complexes. Accordingly, the patterns of GUS activity in these transgenic lines differ and neither of them encompasses all plant tissues even in the presence of saturating levels of exogenous ethylene. Herein, we set out to develop and test a more sensitive version of the ethylene-inducible promoter that we refer to as EBSnew (abbreviated as EBSn). EBSn leverages a tandem of ten non-identical, natural copies of a novel, dual, everted, 11bp-long EIN3-binding site, 2EBS(-1). We show that in Arabidopsis, EBSn outperforms its predecessors in terms of its ethylene sensitivity, having the capacity to monitor endogenous levels of ethylene and displaying more ubiquitous expression in response to the exogenous hormone. We demonstrate that the EBSn promoter is also functional in tomato, opening new avenues to manipulating ethylene-regulated processes, such as ripening and senescence, in crops.

plant biology↗

bioRxiv2025

Arabidopsis lines with modified ascorbate concentrations reveal a link between ascorbate and auxin biosynthesis

Ascorbate is the most abundant water-soluble antioxidant in plants, and it is an essential molecule for normal plant development. It is present in all green plants, with very different concentrations in different plant species. While ascorbate accumulation is a trait of nutritional, and therefore, agronomical interest, the impact of different concentrations over cellular homeostasis remains elusive. In order to shed light over this question, we leveraged Arabidopsis lines with very low ascorbate (vtc2 mutant with 20% of WT ascorbate levels), and low ascorbate concentration (vtc4 mutant with 65% of WT levels), and we generated a line that accumulates 165% of WT levels (vtc2/OE-VTC2). An 80% reduction of ascorbate increased the expression of genes implicated in defense against pathogens, but repressed genes associated with abiotic stress responses. Unexpectedly, lines with increased (165% of WT) and decreased (65% of WT) ascorbate levels shared 85% of induced transcription factors and the GO terms associated with their transcriptional programs. Among the group of genes whose expression is positively correlated with ascorbate content, we identified TAA1/WEI8, a gene encoding a tryptophan aminotransferase that catalyzes the first step of auxin biosynthesis. Using a combination of genetic and pharmacological approaches in fluorescent and histochemical reporter lines for auxin biosynthesis and signaling activity, we revealed that TAA1- and TAA1-RELATED2 (TAR2)-mediated auxin biosynthesis is necessary for plants to cope with increased ascorbate concentration in a light-dependent manner, revealing a new layer of complexity in the regulatory landscape of redox homeostasis.

plant biology↗

bioRxiv2025

DASH: A versatile and high-capacity gene stacking system for plant synthetic biology

DNA assembly systems based on the Golden Gate method are popular in synthetic biology but have several limitations: small insert size, incompatibility with other cloning platforms, DNA domestication requirement, generation of fusion scars, and lack of post-assembly modification. To address these obstacles, we present the DASH assembly toolset, which combines features of Golden Gate-based cloning, recombineering, and site-specific recombinase systems. We developed (1) a set of donor vectors based on the GoldenBraid platform, (2) an acceptor vector derived from the plant transformation-competent artificial chromosome (TAC) vector, pYLTAC17, and (3) a re-engineered recombineering-ready E. coli strain, CZ105, based on SW105. The initial assembly steps are carried out using the donor vectors following standard GoldenBraid assembly procedures. Importantly, existing parts and transcriptional units created using compatible Golden Gate-based systems can be transferred to the DASH donor vectors using standard single-tube restriction/ligation reactions. The cargo DNA from a DASH donor vector is then efficiently transferred in vivo in E. coli into the acceptor vector by the sequential action of a rhamnose-inducible phage-derived PhiC31 integrase and arabinose-inducible yeast-derived Flippase (FLP) recombinase using CZ105. Furthermore, recombineering-based post-assembly modification, including the removal of undesirable scars, is greatly simplified. To demonstrate the utility of the DASH system, a 116 kb DNA construct harboring a 97 kb cargo consisting of 35 transcriptional units was generated. One of the CDSs in the final assembly was replaced through recombineering, and the in planta functionality of the entire construct was tested in both transient and stable transformants.

synthetic biology↗

bioRxiv2024

Targeted DNA ADP-ribosylation triggers templated repair in bacteria and base mutagenesis in eukaryotes

Base editors create precise genomic edits by directing nucleobase deamination or removal without inducing double-stranded DNA breaks. However, a vast chemical space of other DNA modifications remains to be explored for genome editing. Here, we harness the bacterial anti-phage toxin DarT2 to append ADP-ribosyl moieties to DNA, unlocking distinct editing outcomes in bacteria versus eukaryotes. Fusing an attenuated DarT2 to a Cas9 nickase, we program site-specific ADP-ribosylation of thymines within a target DNA sequence. In tested bacteria, targeting drives efficient homologous recombination in tested bacteria, offering flexible and scar-free genome editing without base replacement nor counterselection. In tested eukaryotes including yeast, plants and human cells, targeting drives substitution of the modified thymine to adenine or a mixture of adenine and cytosine with limited insertions or deletions, offering edits inaccessible to current base editors. Altogether, our approach, called append editing, leverages the addition of a chemical moiety to DNA to expand current modalities for precision gene editing.

synthetic biology↗

bioRxiv2024

Development of modular geminivirus-based vectors for high cargo expression and gene targeting in plants

Viral vectors can be useful tools for expressing recombinant proteins as well as delivering gene-editing machinery. Despite their utility, the development and subsequent optimization of these tools is often a difficult and tedious process. Thus, although considerable work has been done to create useful viral vectors for gene editing and protein expression, there is a lack of understanding of how best to design these vectors for specific applications. For instance, it is often unclear whether the inclusion of heterologous promoter sequences or different viral components will improve cargo expression or replicon accumulation. To address some of these hurdles, we designed a GoldenBraid (GB)-compatible viral vector system based on the geminivirus - Beet curly top virus (BCTV). This system allows for simple, modular cloning of a variety of reporter constructs. Making use of this modular cloning strategy, we compared a variety of alternative viral vector architectures. Interestingly, native BCTV promoters outperformed the constitutive 35S promoter, while the removal of the BCTV virion-sense genes promoted reporter expression. Intriguingly, these modifications had no effect on total replicon accumulation. These results show the utility of the new modular BCTV-based viral vectors for protein expression and gene targeting applications, as well as uncover design principles that may inform future geminivirus-based viral vector architectures. We anticipate that the availability of this new modular system will spark the broad adoption of replicon-based strategies in protein expression and gene editing experiments in plants.

synthetic biology↗

bioRxiv2020

Structure-function analysis of interallelic complementation in ROOTY transheterozygotes

Auxin is a crucial plant growth regulator. Forward genetic screens for auxin-related mutants have led to the identification of key genes involved in auxin biosynthesis, transport, and signaling. Loss-of-function mutations in the genes involved in indole glucosinolate biosynthesis, a metabolically-related route that produces defense compounds from indolic precursors shared with the auxin pathway, result in auxin overproduction. We identified an allelic series of fertile, hypomorphic mutants for an essential indole glucosinolate route gene ROOTY (RTY) that show a range of high-auxin defects. Genetic characterization of these lines uncovered phenotypic suppression by cyp79b2 b3, wei2, and wei7 mutants and revealed the phenomenon of interallelic complementation in several RTY transheterozygotes. Structural modeling of RTY shed light on the structure-to-function relations in the RTY homo- and heterodimers and unveiled the likely structural basis of interallelic complementation. This work underscores the importance of employing true null mutants in genetic complementation studies.

genetics↗

bioRxiv2019

An improved plant toolset for high-throughput recombineering

Gene functional studies often rely on the expression of a gene of interest as transcriptional and translational fusions with specialized tags. Ideally, this is done in the native chromosomal contexts to avoid potential misexpression artifacts. Although recent improvements in genome editing make it possible to directly modify the target genes in their native chromosomal location, classical transgenesis is still the preferred experimental approach chosen in most gene tagging studies because of its time efficiency and accessibility. We have developed a recombineering-based tagging system that brings together the convenience of the classical transgenic approaches and the high degree of confidence in the obtained results provided by the direct chromosomal tagging achievable by genome editing strategies. These simple and customizable recombineering toolsets and protocols allow for high-throughput generation of a variety of genetic modifications. In addition, a highly efficient recombinase-mediated cassette exchange system has been developed to facilitate the transfer of the desired sequences from a BAC clone to a transformation-compatible binary vector, expanding the use of the recombineering approaches beyond Arabidopsis. The utility of this system is demonstrated by the generation of over 250 whole-gene translational fusions and 123 Arabidopsis transgenic lines corresponding to 62 auxin-related genes, and the characterization of the translational reporter expression patterns for 14 auxin biosynthesis genes.

plant biology↗