Biology subjects

Melnyk, C. W.

Publications and source records attributed to Melnyk, C. W..

15 recordsLinked to original sources

bioRxiv2024

A long-distance inhibitory system regulates haustoria numbers in parasitic plants

The ability of parasitic plants to withdraw nutrients from their hosts depends on the formation of an infective structure known as the haustorium. How parasites regulate their haustoria numbers is poorly understood, and here, we uncovered that existing haustoria in the facultative parasitic plants Phtheirospermum japonicum and Parentucellia viscosa suppressed the formation of new haustoria on distant roots. Using Phtheirospermum japonicum, we found that this effect depended on the formation of mature haustoria and could be induced through the application of external nutrients. To understand the molecular basis of this root plasticity, we analyzed hormone response and found that existing infections upregulated cytokinin responsive genes first at the haustoria and then more distantly in Phtheirospermum shoots. We observed that infections increased endogenous cytokinin levels in Phtheirospermum roots and shoots, and this increase appeared relevant since local treatments with exogenous cytokinins blocked the formation of both locally and distantly formed haustoria. In addition, local overexpression of a cytokinin degrading enzyme in Phtheirospermum prevented this systemic inter-haustoria repression and increased haustoria numbers locally. We propose that a long-distance signal produced by haustoria negatively regulates future haustoria, and in Phtheirospermum, such a signaling system is mediated by a local increase in cytokinin to regulate haustoria numbers and balance nutrient acquisition.

plant biology↗

bioRxiv2024

Water availability determines plant regeneration fates

Wounding and hormones serve as diverse triggers for regeneration in animals and plants but how organisms determine regeneration outcomes remains largely unknown. Here, we demonstrated that wounded Arabidopsis tissues regenerate two distinct fates, wound-induced callus or de novo root formation, that are driven by antagonizing molecular pathways related to cambium and root development. We discovered that local water availability dictated these regeneration outcomes in Arabidopsis and tomato, with high water triggering root fate and low water initiating callus fate. Moreover, distinct spatial distributions of auxin response maxima were critical for fate progression and water availability regulated these auxin maxima through the hormones ethylene and jasmonic acid. We propose that water availability determines environmental control of regeneration plasticity with applied potential for improving regeneration in agriculture.

plant biology↗

bioRxiv2024

Cell fate plasticity of xylem-pole-pericycle in Arabidopsis roots

In Arabidopsis roots, xylem-pole-pericycle (XPP) cells exhibit remarkable cell fate plasticity by contributing to both lateral root (LR) and cambium formation. Despite significant progress in understanding these individual processes, the mechanism orchestrating these two fates and their effects on root architecture and secondary growth remain unclear. Here we combined lineage tracing with molecular genetics to study the fate dynamics of XPP cells. We showed that developmentally arrested lateral root primordia (LRP) that fail to emerge as lateral roots, gradually obtain cambium identity thus contributing to secondary growth. Conversely, preestablished procambium identity within XPP cells can be reverted to LR identity when simulated by auxin, an important player in LR development. This competence for auxin-induced LR formation from XPP cells, termed LR potency, however, decreases as the root matures. We found key cambium regulators play essential roles in shaping LR potency by promoting cambium activation and inhibiting LR development. Consistently, corresponding mutants with impaired cambium activity display broader LR potency. Moreover, cytokinins, essential players in cambium development, facilitate the identity transition of LRPs to cambium and reduce LR potency through key cambium regulators. Overall, our findings highlight the inherent cellular plasticity of XPP cells and elucidate how plant hormones influence root architecture and secondary growth through balancing the two cell fates of XPP cells.

plant biology↗

bioRxiv2023

A conserved graft formation process in Picea abies and Arabidopsis thaliana identifies the PAT gene family as central regulators of wound healing

The widespread use of plant grafting has enabled eudicots and gymnosperms to join with closely related species and grow as one. Gymnosperms have dominated forests for over 200 million years and despite their economic and ecological relevance, we know little about how they graft. Here, we developed a micrografting method in conifers using young tissues that allowed efficient grafting between closely related species and distantly related genera. Conifer graft junctions rapidly connected vasculature and differentially expressed thousands of genes including auxin and cell wall-related genes. By comparing these genes to those induced during Arabidopsis thaliana graft formation, we found a common activation of cambium, cell division, phloem and xylem-related genes. A gene regulatory network analysis in Picea abies (Norway spruce) predicted that PHYTOCHROME A SIGNAL TRANSDUCTION 1 (PAT1) acted as a core regulator of graft healing. This gene was strongly upregulation during both P. abies and Arabidopsis grafting, and Arabidopsis mutants lacking PAT-genes failed to attach tissues or successfully graft. Complementing Arabidopsis PAT mutants with the P. abies PAT1 homolog rescued tissue attachment and enhance callus formation. Together, our data demonstrate an ability for young tissues to facilitate grafting with distantly related species and identifies the PAT gene family as conserved regulators of graft healing and tissue regeneration.

plant biology↗

bioRxiv2023

Auxin signaling in the cambium promotes tissue attachment and vascular development during Arabidopsis thaliana graft formation

The remarkable ability of plants to regenerate wounds is exemplified during the process of plant grafting when two plants are cut and joined together to grow as one. During graft healing, damaged tissues attach, cells proliferate and the vasculatures connect to form a graft union. The plant hormone auxin plays a central role and mutants perturbed in auxin response fail to successfully graft. Here, we investigated the role of individual cell types and their response to auxin during Arabidopsis thaliana graft formation. By employing an inducible misexpression system, we blocked auxin response in individual cell types using the bodenlos mutation. We found that auxin signaling in procambial tissues was critical for both successful tissue attachment and also for vascular differentiation. In addition, we found that auxin signaling was required for cell divisions of the procambial cells during graft formation. Loss of function mutants in cambial pathways also perturbed attachment and phloem reconnection. We propose that cambium and procambium are key tissues that allow both tissue attachment and vascular differentiation during successful grafting. Our study thus refines our knowledge of graft development and furthers our understanding of regeneration biology and the function of cambium.

plant biology↗

bioRxiv2023

Damage activates EVG1 to suppress vascular differentiation during regeneration in Arabidopsis thaliana

Plants possess remarkable regenerative abilities to form de novo vasculature after damage and in response to pathogens that invade and withdraw nutrients. To look for common factors that affect vascular formation upon stress, we searched for Arabidopsis thaliana genes differentially expressed during Agrobacterium infection, nematode infection and plant grafting. One such gene was cell-wall associated and highly induced by all three stresses. Mutations in it enhanced ectopic xylem formation in Vascular cell Induction culture System Using Arabidopsis Leaves (VISUAL) and enhanced graft formation and was thus named ENHANCER OF VISUAL AND GRAFTING 1 (EVG1). Mutated evg1 inhibited cambium development and callus formation yet promoted tissue attachment, syncytium size, phloem reconnection and xylem formation. evg1 affected abscisic acid and cell wall responses and was itself down regulated by ABA. We found mutations in a receptor-like gene, RLP44, had the same regeneration phenotype as EVG1 mutations including enhancing VISUAL and grafting. evg1 and rlp44 mutants affected the expression of many genes in common including those important for successful regeneration and vascular formation. We propose that EVG1 integrates information from cutting, wounding or parasitism stresses and functions with RLP44 to suppress vascular differentiation during regeneration.

plant biology↗

bioRxiv2023

PME-mediated pectin modifications promote haustoria initiation and xylem bridge development in the parasitic plant Phtheirospermum japonicum

O_LIParasitic plants produce cell wall modifying enzymes that are thought to be important for efficient host infection. Here, we investigated the role of pectin methylesterases (PMEs) and their inhibitors (PMEIs) during haustorium development in the facultative parasitic plant Phtheirospermum japonicum infecting Arabidopsis thaliana. C_LIO_LIWe employed immunohistochemistry to characterise tissue-specific changes in pectin methylesterification during haustorium development. We found putative PME and PMEI genes in P. japonicum and used genetic and transcriptomic approaches to identify those involved in haustorium development. C_LIO_LIOur results show tissue-specific changes in pectin methylesterification during haustorium development. De-methylesterified pectin correlated with haustorial intrusive cells whereas highly methylated pectin correlated with vascular tissues. We also found that inhibition of PME activity delayed haustoria development and xylem connectivity. Several PjPME and PjPMEI genes increased expression specifically during haustorium development but such increases did not occur when haustorium initiation or xylem connections were blocked by chemical treatment. C_LIO_LIThis study describes the importance of pectin modifications in parasitic plants during host infection. Our results suggest a dynamic regulation of PMEs and PMEIs contributes to haustoria initiation and to the establishment of xylem connections between parasite and host. C_LI

plant biology↗

bioRxiv2021

The regeneration factors ERF114 and ERF115 act as transducers of mechanical cues to developmental pathways

Plants show an unparalleled regenerative capacity, allowing them to survive severe stress conditions, such as injury, herbivory attack and harsh weather conditions. This potential not only replenishes tissues and restores damaged organs, but can also give rise to whole plant bodies, highlighting the intertwined nature of development and regeneration. It suggests that regeneration and developmental processes respond to the same upstream signals, but how a cell knows which of the two processes to engage is currently unknown. Here, we demonstrate that next to being regulators of regeneration, ETHYENE RESPONSE FACTOR 114 (ERF114) and ERF115 govern developmental growth in the absence of wounding or injury. Increased ERF114 and ERF115 activity is correlated with enhanced xylem maturation and lateral root formation, whereas their knockout results in a decrease in lateral roots and xylem connectivity following grafting. Moreover, we provide evidence that mechanical cues contribute to ERF114 and ERF115 expression in correlation with BZR1 mediated brassinosteroid signaling under both regenerative and developmental conditions. Antagonistically, negative regulation of cell wall extensibility via cell wall-associated mechanosensory FERONIA signaling suppresses their expression under both conditions. Our data suggest a molecular framework in which mechanical perturbations too great to be compensated by adaptive cell wall remodeling results in strong ERF114 and ERF115 expression, switching their role from developmental to regenerative regulators. One-Sentence SummaryMechanical cues drive ERF114/ERF115 expression during lateral root development as well as regeneration.

plant biology↗

bioRxiv2021

High temperature perception in leaves promotes vascular regeneration in distant tissues

Cellular regeneration in response to wounding is fundamental to maintain tissue integrity. Various internal factors including hormones and developmental pathways affect wound healing but little is known about how external factors influence regeneration. To better understand how the environment affects regeneration, we investigated the effects of temperature using the horticulturally relevant process of plant grafting. We found that elevated temperatures accelerated vascular regeneration of Arabidopsis thaliana and tomato (Solanum lycopersicum) grafts. Leaves were critical for this effect since blocking auxin transport or mutating PHYTOCHROME INTERACTING FACTOR4 (PIF4) or YUCCA2/5/8/9 in the cotyledons abolished the temperature enhancement. However, these perturbations had no effect upon graft healing at ambient temperatures and mutations in PIF4 did not affect the temperature enhancement of callus formation or tissue adhesion, suggesting that leaf-derived auxin was specific for enhancing vascular regeneration in response to elevated temperatures. Tissue-specific perturbations of auxin response using a BODENLOS (BDL) mutant revealed an asymmetric effect of temperature upon regeneration: the presence of bdl above the cut prevented temperature enhancement whereas the presence of bdl below the cut prevented graft healing regardless of temperature. Promotion of tissue regeneration by elevated temperatures was not specific for graft healing and we found that elevated temperatures accelerated xylem formation between the parasite Phtheirospermum japonicum and host Arabidopsis thaliana, and this effect required shoot-derived auxin from the parasite. Taken together, our results identify a pathway by which elevated temperatures accelerate vascular development which could be of relevance for improving regeneration and better understanding inter-plant vascular connections.

plant biology↗

bioRxiv2021

Nitrates increase abscisic acid levels to regulate haustoria formation in the parasitic plant Phtheirospermum japonicum

Parasitic plants are globally prevalent pathogens that withdraw nutrients from their host plants using an organ known as the haustorium. Some, the obligate parasites are entirely dependent on their hosts for survival, whereas others, the facultative parasites, are independent of their hosts and infect depending on environmental conditions and the presence of the host. How parasitic plants regulate their haustoria in response to their environment is largely unknown. Using the facultative root parasite Phtheirospermum japonicum, we found that external nutrient levels modified haustorial numbers. This effect was independent of phosphate and potassium but nitrates were sufficient and necessary to block haustoria formation. Elevated nitrate levels prevented the activation of hundreds of genes associated with haustoria formation, downregulated genes associated with xylem development and increased levels of abscisic acid (ABA). Enhancing ABA levels independently of nitrates blocked haustoria formation whereas reducing ABA biosynthesis allowed haustoria to form in the presence of nitrates suggesting that nitrates mediated haustorial regulation in part via ABA production. Nitrates also inhibited haustoria formation and reduced infectivity of the obligate root parasite Striga hermonthica, suggesting a more widely conserved mechanism by which parasitic plants adapt their extent of parasitism according to nitrogen availability in the external environment.

plant biology↗

bioRxiv2021

Analysis of phloem trajectory links tissue maturation to cell specialization.

The mechanisms that allow cells in the plant meristem to coordinate tissue-wide maturation gradients with specialized cell networks are critical for indeterminate growth. Here, we reconstructed the protophloem developmental trajectory of 19 cells from cell birth to terminal differentiation at single cell resolution in the Arabidopsis root. We found that cellular specification is mediated near the stem cell niche by PHLOEM EARLY DOF (PEAR) transcription factors. However, the PEAR dependent differentiation program is repressed by a broad gradient of PLETHORA (PLT) transcription factors, which directly inhibit PEARs own direct target ALTERED PHLOEM DEVELOPMENT (APL). The dissipation of PLT gradient around 7 cells from the stem cell activates APL expression, and a subsequent transitional network that results in a "seesaw" pattern of mutual inhibition over developmental time. Together, we provide a mechanistic understanding of how morphogen-like maturation gradients interface with cell-type specific transcriptional regulators to stage cellular differentiation.

plant biology↗

bioRxiv2020

Bipartite influence of abscisic acid on xylem differentiation trajectories is dependent on distinct VND transcription factors in Arabidopsis

Plants display a remarkable ability to adjust their growth and development to changes in environmental conditions, such as reduction in water availability. This high degree of plasticity is apparent not only as altered root and shoot growth rates, but also as changes to tissue patterning and cell morphology [1,2]. We have previously shown that Arabidopsis thaliana root xylem displays plastic developmental responses to limited water availability, mediated by non-cell autonomous action of abscisic acid, ABA [2]. Here, we show through analyses of ABA response reporters and tissue specific suppression of ABA signalling that xylem cells act as primary signalling centres for mediation of changes to both xylem cell fate and differentiation rate revealing a cell autonomous control of xylem development by ABA. Transcriptomic changes in response to ABA showed that members of the VASCULAR RELATED NAC DOMAIN (VND) transcription factor family are rapidly activated. Molecular and genetic analyses revealed that the two aspects of xylem developmental changes, cell fate and differentiation rate, are dependent on distinct members of this transcription factor family. Thus, this study provides insights into how different aspects of developmental plasticity can be interlinked, yet genetically independent of each other. Moreover, similarities in phenotypic and molecular responses to ABA in diverse species indicate an evolutionary conservation of the ABA-xylem development regulatory network among eudicots. Hence, this study gives molecular insights on how environmental stress promotes anatomical plasticity to key plant traits with potential relevance for water use optimization and adaptation to drought conditions.

plant biology↗

bioRxiv2019

Shoot-to-root translocation of the jasmonate precursor 12-oxo-phytodienoic acid (OPDA) coordinates plant growth responses following tissue damage

Multicellular organisms rely upon the movement of signaling molecules across cells, tissues and organs to communicate among distal sites. In plants, herbivorous insects, necrotrophic pathogens and mechanical wounding stimulate the activation of the jasmonate (JA) pathway, which in turn triggers the transcriptional changes necessary to protect plants against those challenges, often at the expense of growth. Although previous evidence indicated that JA species can translocate from damaged into distal sites, the identity of the mobile compound(s), the tissues through which they translocate and the consequences of their relocation remain unknown. Here, we demonstrated that endogenous JA species generated after shoot injury translocate to unharmed roots via the phloem vascular tissue in Arabidopsis thaliana. By wounding wild-type shoots of chimeric plants and by quantifying the relocating compounds from their JA-deficient roots, we uncovered that the JA-Ile precursor 12-oxo-phytodienoic acid (OPDA) is a mobile JA species. Our data also showed that OPDA is a primary mobile compound relocating to roots where, upon conversion to the bioactive hormone, it induces JA-mediated gene expression and root growth inhibition. Collectively, our findings reveal the existence of long-distance transport of endogenous OPDA which serves as a communication molecule to coordinate shoot-to-root responses, and highlight the importance of a controlled distribution of JA species among organs during plant stress acclimation.

plant biology↗

bioRxiv2017

Nitrate modulates stem cell dynamics by regulating WUSCHEL expression through cytokinins

The shoot apical meristem (SAM) is responsible for the generation of all of the aerial parts of plants1. Given its critical role, dynamical changes in SAM activity should play a central role in the adaptation of plant architecture to the environment2. Using quantitative microscopy, grafting experiments and genetic perturbations, we connect the plant environment to the SAM, by describing the molecular mechanism by which cytokinins signal the level of nutrient availability to the SAM. We show that a systemic signal of cytokinin precursors3 mediates the adaptation of SAM size and organogenesis rate to the availability of mineral nutrients by modulating the expression of WUSCHEL, a key regulator of stem cell homeostasis4. In time-lapse experiments, we further show that this mechanism allows meristems to adapt to rapid changes in nitrate concentration, and thereby modulate their rate of organ production to the availability of mineral nutrients within a few days. Our work sheds new light on the role of the stem cell regulatory network, by showing that it does not only maintain meristem homeostasis but also allows plants to adapt to rapid changes in the environment.

plant biology↗

bioRxiv2017

Gene expression dynamics and inter-tissue recognition mechanisms during tissue fusion at the Arabidopsis graft junction

The ability for cut tissues to join together and form a chimeric organism is a remarkable property of many plants, however, grafting is poorly characterized at the molecular level. To better understand this process we monitored genome-wide temporal and spatial gene expression changes in grafted Arabidopsis thaliana hypocotyls. Tissues above and below the graft rapidly developed an asymmetry such that many genes were more highly expressed on one side than the other. This asymmetry correlated with sugar responsive genes and we observed an accumulation of starch above the graft that decreased along with asymmetry once the sugar-transporting vascular tissues reconnected. Despite the initial starvation response below the graft, many genes associated with vascular formation were rapidly activated in grafted tissues but not in cut and separated tissues indicating that a recognition mechanism activated that was independent of functional vascular connections. Auxin which is transported cell-to-cell, had a rapidly elevated response that was symmetric, suggesting that auxin was perceived by the root within hours of tissue attachment to activate the vascular regeneration process. A subset of genes were expressed only in grafted tissues, indicating that wound healing proceeded via different mechanisms depending on the presence or absence of adjoining tissues. Such a recognition process could have broader relevance for tissue regeneration, inter-tissue communication and tissue fusion events.

plant biology↗