Light at the end of the tunnel: integrating signaling pathways in the coordination of lateral root development.

Root system architecture (RSA) encompasses a range of physical root attributes, including the lateral roots (LRs), root hairs and adventitious roots, in addition to the primary or main root. This overall structure is a crucial trait for efficient water and mineral capture alongside providing anchorage to the plant in the soil and is vital for plant productivity and fitness. RSA dynamics are dependent upon various environmental cues such as light, soil pH, water, mineral nutrition and the belowground microbiome. Among these factors, light signaling through HY5 significantly influences the flexibility of RSA by controlling different signaling pathways that converge at photoreceptors-mediated signaling, also present in the 'hidden half'. Furthermore, several phytohormones also drive the formation and emergence of LRs and are critical to harmonize intra and extracellular stimuli in this regard. This review endeavors to elucidate the impact of these interactions on RSA, with particular emphasis on LR development and to enhance our understanding of the fundamental mechanisms governing the light-regulation of LR growth and physiology.

Molecular dialogue between light and temperature signaling in plants: From perception to thermotolerance.

Light and temperature are the two most variable environmental signals, which significantly regulate plant growth and development. Plants in the natural environment usually encounter warmer temperatures during the day and cooler temperatures at night, suggesting both light and temperature are closely linked signals. Due to global warming, it has become important to understand how light and temperature signaling pathways converge, and regulate plant development. This review outlines diverse mechanisms of light and temperature perception and downstream signaling, with an emphasis on their integration and interconnection. The recent research has highlighted the regulation of thermomorphogenesis by photoreceptors and their downstream light signaling proteins under different light conditions, and circadian clock components at warm temperatures. We have made an attempt to comprehensively describe these studies and demonstrate their connection with plant developmental responses. We have also explained how gene signaling pathways of light and thermomorphogenesis, are interconnected with HSR-mediated thermotolerance, which reveals new avenues to manipulate plants for climate resilience. In addition, the role of sugars as signaling molecules between light and temperature is also highlighted. Thus, we envisage that such detailed knowledge will enhance the understanding of how plants perceive light and temperature cues simultaneously and bring about responses that help in their adaptation.

MEDIATOR SUBUNIT17 integrates jasmonate and auxin signaling pathways to regulate thermomorphogenesis.

Plant adjustment to environmental changes involves complex crosstalk between extrinsic and intrinsic cues. In the past two decades, extensive research has elucidated the key roles of PHYTOCHROME-INTERACTING FACTOR4 (PIF4) and the phytohormone auxin in thermomorphogenesis. In this study, we identified a previously unexplored role of jasmonate (JA) signaling components, the Mediator complex, and their integration with auxin signaling during thermomorphogenesis in Arabidopsis (Arabidopsis thaliana). Warm temperature induces expression of JA signaling genes including MYC2, but, surprisingly, this transcriptional activation is not JA dependent. Warm temperature also promotes accumulation of the JA signaling receptor CORONATINE INSENSITIVE1 (COI1) and degradation of the JA signaling repressor JASMONATE-ZIM-DOMAIN PROTEIN9, which probably leads to de-repression of MYC2, enabling it to contribute to the expression of MEDIATOR SUBUNIT17 (MED17). In response to warm temperature, MED17 occupies the promoters of thermosensory genes including PIF4, YUCCA8 (YUC8), INDOLE-3-ACETIC ACID INDUCIBLE19 (IAA19), and IAA29. Moreover, MED17 facilitates enrichment of H3K4me3 on the promoters of PIF4, YUC8, IAA19, and IAA29 genes. Interestingly, both occupancy of MED17 and enrichment of H3K4me3 on these thermomorphogenesis-related promoters are dependent on PIF4 (or PIFs). Altered accumulation of COI1 under warm temperature in the med17 mutant suggests the possibility of a feedback mechanism. Overall, this study reveals the role of the Mediator complex as an integrator of JA and auxin signaling pathways during thermomorphogenesis.

Jasmonic acid coordinates with light, glucose and auxin signalling in regulating branching angle of Arabidopsis lateral roots.

The role of jasmonates (JAs) in primary root growth and development and in plant response to external stimuli is already known. However, its role in lateral root (LR) development remains to be explored. Our work identified methyl jasmonate (MeJA) as a key phytohormone in determining the branching angle of Arabidopsis LRs. MeJA inclines the LRs to a more vertical orientation, which was dependent on the canonical JAR1-COI1-MYC2,3,4 signalling. Our work also highlights the dual roles of light in governing LR angle. Light signalling enhances JA biosynthesis, leading to erect root architecture; whereas, glucose (Glc) induces wider branching angles. Combining physiological and molecular assays, we revealed that Glc antagonises the MeJA response via TARGET OF RAPAMYCIN (TOR) signalling. Moreover, physiological assays using auxin mutants, MYC2-mediated transcriptional activation of LAZY2, LAZY4 and auxin biosynthetic gene CYP79B2, and asymmetric distribution of DR5::GFP and PIN2::GFP pinpointed the role of an intact auxin machinery required by MeJA for vertical growth of LRs. We also demonstrated that light perception and signalling are indispensable for inducing vertical angles by MeJA. Thus, our investigation highlights antagonism between light and Glc signalling and how they interact with JA-auxin signals to optimise the branching angle of LRs.

The social network of target of rapamycin complex 1 in plants.

Target of rapamycin complex 1 (TORC1) is a highly conserved serine-threonine protein kinase crucial for coordinating growth according to nutrient availability in eukaryotes. It works as a central integrator of multiple nutrient inputs such as sugar, nitrogen, and phosphate and promotes growth and biomass accumulation in response to nutrient sufficiency. Studies, especially in the past decade, have identified the central role of TORC1 in regulating growth through interaction with hormones, photoreceptors, and stress signaling machinery in plants. In this review, we comprehensively analyse the interactome and phosphoproteome of the Arabidopsis TORC1 signaling network. Our analysis highlights the role of TORC1 as a central hub kinase communicating with the transcriptional and translational apparatus, ribosomes, chaperones, protein kinases, metabolic enzymes, and autophagy and stress response machinery to orchestrate growth in response to nutrient signals. This analysis also suggests that along with the conserved downstream components shared with other eukaryotic lineages, plant TORC1 signaling underwent several evolutionary innovations and co-opted many lineage-specific components during. Based on the protein-protein interaction and phosphoproteome data, we also discuss several uncharacterized and unexplored components of the TORC1 signaling network, highlighting potential links for future studies.

A glucose-target of rapamycin signaling axis integrates environmental history of heat stress through maintenance of transcription-associated epigenetic memory in Arabidopsis.

In nature, plants cope with adversity and have established strategies that recall past episodes and enable them to better cope with stress recurrences by establishing a 'stress memory'. Emerging evidence suggests that glucose (Glc) and target of rapamycin (TOR), central regulators of plant growth, have remarkable functions in stress adaptation. However, whether TOR modulates a stress memory response is so far unknown. Global transcriptome profiling identified that Glc, through TOR, regulates the expression of numerous genes involved in thermomemory. Priming of TOR overexpressors with mild heat showed better stress endurance, whereas TOR RNAi showed reduced thermomemory. This thermomemory is linked with histone methylation at specific sites of heat stress (HS) genes. TOR promotes long-term accumulation of H3K4me3 on thermomemory-associated gene promoters, even when transcription of those genes reverts to their basal level. Our results suggest that ARABIDOPSIS TRITHORAX 1 (ATX1), an H3K4 methyltransferase already shown to regulate H3K4me3 levels at the promoters of HS recovery genes, is a direct target of TOR signaling. The TOR-activating E2Fa binds to the promoter of ATX1 and regulates its expression, which ultimately regulates thermomemory. Collectively, our findings reveal a mechanistic framework in which Glc-TOR signaling determines the integration of stress and energy signaling to regulate thermomemory.

Role of sugar and auxin crosstalk in plant growth and development.

Under the natural environment, nutrient signals interact with phytohormones to coordinate and reprogram plant growth and survival. Sugars are important molecules that control almost all morphological and physiological processes in plants, ranging from seed germination to senescence. In addition to their functions as energy resources, osmoregulation, storage molecules, and structural components, sugars function as signaling molecules and interact with various plant signaling pathways, such as hormones, stress, and light to modulate growth and development according to fluctuating environmental conditions. Auxin, being an important phytohormone, is associated with almost all stages of the plant's life cycle and also plays a vital role in response to the dynamic environment for better growth and survival. In the previous years, substantial progress has been made that showed a range of common responses mediated by sugars and auxin signaling. This review discusses how sugar signaling affects auxin at various levels from its biosynthesis to perception and downstream gene activation. On the same note, the review also highlights the role of auxin signaling in fine-tuning sugar metabolism and carbon partitioning. Furthermore, we discussed the crosstalk between the two signaling machineries in the regulation of various biological processes, such as gene expression, cell cycle, development, root system architecture, and shoot growth. In conclusion, the review emphasized the role of sugar and auxin crosstalk in the regulation of several agriculturally important traits. Thus, engineering of sugar and auxin signaling pathways could potentially provide new avenues to manipulate for agricultural purposes.

Understanding the Intricate Web of Phytohormone Signalling in Modulating Root System Architecture.

Root system architecture (RSA) is an important developmental and agronomic trait that is regulated by various physical factors such as nutrients, water, microbes, gravity, and soil compaction as well as hormone-mediated pathways. Phytohormones act as internal mediators between soil and RSA to influence various events of root development, starting from organogenesis to the formation of higher order lateral roots (LRs) through diverse mechanisms. Apart from interaction with the external cues, root development also relies on the complex web of interaction among phytohormones to exhibit synergistic or antagonistic effects to improve crop performance. However, there are considerable gaps in understanding the interaction of these hormonal networks during various aspects of root development. In this review, we elucidate the role of different hormones to modulate a common phenotypic output, such as RSA in Arabidopsis and crop plants, and discuss future perspectives to channel vast information on root development to modulate RSA components.

Glucose-Regulated HLP1 Acts as a Key Molecule in Governing Thermomemory.

Induction of heat shock proteins (HSPs) in response to heat stress (HS) is indispensable for conferring thermotolerance. Glc, a fundamental signaling and metabolic molecule, provides energy to stressed seedlings to combat stress. The recovery of stressed plants from detrimental HS in response to Glc is largely mediated by HSPs, but the mechanistic basis of this thermotolerance is not well defined. In this study, we show that Glc has a prominent role in providing thermotolerance. Glc-mediated thermotolerance involves HSP induction via the TARGET OF RAPAMYCIN (TOR)-E2Fa signaling module. Apart from HSPs, TOR-E2Fa also regulates the Arabidopsis (Arabidopsis thaliana) ortholog of human Hikeshi, named HIKESHI-LIKE PROTEIN1 (HLP1). Expression of proHLP1::GUS in the shoot apical meristem (SAM) after HS coincides with TOR-E2Fa expression, substantiating a role for TOR-E2Fa-HLP1 in providing thermotolerance. We also demonstrate that Glc along with heat could induce proliferation activity in the SAM after HS recovery, which was arrested by the TOR inhibitor AZD-8055. Molecular and physiological studies suggest that HS-activated heat stress transcription factor A1s also positively regulate HLP1 transcription, suggesting convergence of the Glc and HS signaling pathways. Loss of functional HLP1 causes HS hypersensitivity, whereas HLP1 overexpressors display increased thermotolerance. HLP1 binds to the promoters of Glc-regulated HS-responsive genes and promotes chromatin acetylation. In addition, Glc modifies the chromatin landscape at thermomemory-related loci by promoting H3K4 trimethylation (H3K4me3). Glc-primed accumulation of H3K4me3 at thermomemory-associated loci is mediated through HLP1. These findings reveal the novel function of Glc-regulated HLP1 in mediating thermotolerance/thermomemory response.

The FCS-like zinc finger scaffold of the kinase SnRK1 is formed by the coordinated actions of the FLZ domain and intrinsically disordered regions.

The SNF1-related protein kinase 1 (SnRK1) is a heterotrimeric eukaryotic kinase that interacts with diverse proteins and regulates their activity in response to starvation and stress signals. Recently, the FCS-like zinc finger (FLZ) proteins were identified as a potential scaffold for SnRK1 in plants. However, the evolutionary and mechanistic aspect of this complex formation is currently unknown. Here, in silico analyses predicted that FLZ proteins possess conserved intrinsically disordered regions (IDRs) with a propensity for protein binding in the N and C termini across the plant lineage. We observed that the Arabidopsis FLZ proteins promiscuously interact with SnRK1 subunits, which formed different isoenzyme complexes. The FLZ domain was essential for mediating the interaction with SnRK1α subunits, whereas the IDRs in the N termini facilitated interactions with the ß and ßγ subunits of SnRK1. Furthermore, the IDRs in the N termini were important for mediating dimerization of different FLZ proteins. Of note, the interaction of FLZ with SnRK1 was confined to cytoplasmic foci, which colocalized with the endoplasmic reticulum. An evolutionary analysis revealed that in general, the IDR-rich regions are under more relaxed selection than the FLZ domain. In summary, the findings in our study reveal the structural details, origin, and evolution of a land plant-specific scaffold of SnRK1 formed by the coordinated actions of IDRs and structured regions in the FLZ proteins. We propose that the FLZ protein complex might be involved in providing flexibility, thus enhancing the binding repertoire of the SnRK1 hub in land plants.

FCS-like zinc finger 6 and 10 repress SnRK1 signalling in Arabidopsis.

SNF1-related protein kinase 1 (SnRK1) is a central regulator of plant growth during energy starvation. The FCS-like zinc finger (FLZ) proteins have recently been identified as adaptor proteins which facilitate the interaction of SnRK1 with other proteins. In this study, we found that two starvation-induced FLZ genes, FLZ6 and FLZ10, work as repressors of SnRK1 signalling. The reduced expression of these genes resulted in an increase in the level of SnRK1α1, which is the major catalytic subunit of SnRK1. This lead to a concomitant increase in phosphorylated protein and SnRK1 activity in the flz6 and flz10 mutants. FLZ6 and FLZ10 specifically interact with SnRK1α subunits in the cytoplasmic foci, which co-localized with the endoplasmic reticulum. In physiological assays, similar to the SnRK1α1 overexpression line, flz mutants showed compromised growth. Further, growth promotion in response to favourable growth conditions was found to be attenuated in the mutants. The enhanced SnRK1 activity in the mutants resulted in a reduction in the level of phosphorylated RIBOSOMAL S6 KINASE and the expression of E2Fa and its targets, indicating that TARGET OF RAPAMYCIN-dependent promotion of protein synthesis and cell cycle progression is impaired. Taken together, this study uncovers a plant-specific modulation of SnRK1 signalling.

Evolution of TOR-SnRK dynamics in green plants and its integration with phytohormone signaling networks.

The target of rapamycin (TOR)-sucrose non-fermenting 1 (SNF1)-related protein kinase 1 (SnRK1) signaling is an ancient regulatory mechanism that originated in eukaryotes to regulate nutrient-dependent growth. Although the TOR-SnRK1 signaling cascade shows highly conserved functions among eukaryotes, studies in the past two decades have identified many important plant-specific innovations in this pathway. Plants also possess SnRK2 and SnRK3 kinases, which originated from the ancient SnRK1-related kinases and have specialized roles in controlling growth, stress responses and nutrient homeostasis in plants. Recently, an integrative picture has started to emerge in which different SnRKs and TOR kinase are highly interconnected to control nutrient and stress responses of plants. Further, these kinases are intimately involved with phytohormone signaling networks that originated at different stages of plant evolution. In this review, we highlight the evolution and divergence of TOR-SnRK signaling components in plants and their communication with each other as well as phytohormone signaling to fine-tune growth and stress responses in plants.

Multiple Interactions between Glucose and Brassinosteroid Signal Transduction Pathways in Arabidopsis Are Uncovered by Whole-Genome Transcriptional Profiling.

Brassinosteroid (BR) and glucose (Glc) regulate many common responses in plants. Here, we demonstrate that under etiolated growth conditions, extensive interdependence/overlap occurs between BR- and Glc-regulated gene expression as well as physiological responses. Glc could regulate the transcript level of 72% of BR-regulated genes at the whole-genome level, of which 58% of genes were affected synergistically and 42% of genes were regulated antagonistically. Presence of Glc along with BR in medium could affect BR induction/repression of 85% of BR-regulated genes. Glc could also regulate several genes involved in BR metabolism and signaling. Both BR and Glc coregulate a large number of genes involved in abiotic/biotic stress responses and growth and development. Physiologically, Glc and BR interact to regulate hypocotyl elongation growth of etiolated Arabidopsis (Arabidopsis thaliana) seedlings in a dose-dependent manner. Glc may interact with BR via a hexokinase1 (HXK1)-mediated pathway to regulate etiolated hypocotyl elongation. Brassinosteroid insensitive1 (BRI1) is epistatic to HXK1, as the Glc insensitive2bri1-6 double mutant displayed severe defects in hypocotyl elongation growth similar to its bri1-6 parent. Analysis of Glc and BR sensitivity in mutants defective in auxin response/signaling further suggested that Glc and BR signals may converge at S-phase kinase-associated protein1-Cullin-F-box-transport inhibitor response1/auxin-related f-box-auxin/indole-3-acetic acid-mediated auxin-signaling machinery to regulate etiolated hypocotyl elongation growth in Arabidopsis.

Interaction between glucose and brassinosteroid during the regulation of lateral root development in Arabidopsis.

Glucose (Glc) plays a fundamental role in regulating lateral root (LR) development as well as LR emergence. In this study, we show that brassinosteroid (BR) signaling works downstream of Glc in controlling LR production/emergence in Arabidopsis (Arabidopsis thaliana) seedlings. Glc and BR can promote LR emergence at lower concentrations, while at higher concentrations, both have an inhibitory effect. The BR biosynthesis and perception mutants showed highly reduced numbers of emerged LRs at all the Glc concentrations tested. BR signaling works downstream of Glc signaling in regulating LR production, as in the glucose insensitive2-1brassinosteroid insensitive1 double mutant, Glc-induced LR production/emergence was severely reduced. Differential auxin distribution via the influx carriers AUXIN RESISTANT1/LIKE AUXIN RESISTANT1-3 and the efflux carrier PIN-FORMED2 plays a central role in controlling LR production in response to Glc and BR. Auxin signaling components AUXIN RESISTANT2,3 and SOLITARY ROOT act downstream of Glc and BR. AUXIN RESPONSE FACTOR7/19 work farther downstream and control LR production by regulating the expression of LATERAL ORGAN BOUNDARIES-DOMAIN29 and EXPANSIN17 genes. Increasing light flux could also mimic the Glc effect on LR production/emergence. However, increased light flux could not affect LR production in those BR and auxin signaling mutants that were defective for Glc-induced LR production. Altogether, our study suggests that, under natural environmental conditions, modulation of endogenous sugar levels can manipulate root architecture for optimized development by altering its nutrient/water uptake as well as its anchorage capacity.

The interaction between glucose and cytokinin signal transduction pathway in Arabidopsis thaliana.

Cytokinins (CKs) and glucose (GLC) control a number of common responses in plants. We hypothesize that there may be an extensive overlap between CK- and GLC-signalling pathways. Microarray along with physiological analysis has been performed to find out the interdependence/overlap between CK and GLC signal transduction pathways in Arabidopsis seedlings. GLC could transcriptionally affect 76% of CK-regulated genes at whole genome level, 89% of which are agonistically regulated. GLC may also affect CK-regulated gene expression via non-transcriptional pathways. GLC can regulate several genes involved in CK metabolism and signalling. A number of gene families involved in development and stress are commonly regulated by CK and GLC. Physiologically, both GLC and CK could regulate hypocotyl length in dark. GLC and CK signalling may integrate at the level of type A Arabidopsis response regulators (ARRs) in controlling hypocotyl length. Both GLC and CK signalling cannot alter hypocotyl length in dark in auxin-signalling mutants auxin response2/indole-3-acetic acid7 (AXR2/IAA7) and AXR3/IAA17 suggesting that they may involve auxin-signalling component as a nodal point. Here, we demonstrate that there is an extensive overlap between CK- and GLC-regulated gene expression and physiological responses.

Glucose control of root growth direction in Arabidopsis thaliana.

Directional growth of roots is a complex process that is modulated by various environmental signals. This work shows that presence of glucose (Glc) in the medium also extensively modulated seedling root growth direction. Glc modulation of root growth direction was dramatically enhanced by simultaneous brassinosteroid (BR) application. Glc enhanced BR receptor BRASSINOSTEROID INSENSITIVE1 (BRI1) endocytosis from plasma membrane to early endosomes. Glc-induced root deviation was highly enhanced in a PP2A-defective mutant, roots curl in naphthyl phthalamic acid 1-1 (rcn1-1) suggesting that there is a role of phosphatase in Glc-induced root-growth deviation. RCN1, therefore, acted as a link between Glc and the BR-signalling pathway. Polar auxin transport worked further downstream to BR in controlling Glc-induced root deviation response. Glc also affected other root directional responses such as root waving and coiling leading to altered root architecture. High light intensity mimicked the Glc-induced changes in root architecture that were highly reduced in Glc-signalling mutants. Thus, under natural environmental conditions, changing light flux in the environment may lead to enhanced Glc production/response and is a way to manipulate root architecture for optimized development via integrating several extrinsic and intrinsic signalling cues.

Sugar signals pedal the cell cycle!

Cell cycle involves the sequential and reiterative progression of important events leading to cell division. Progression through a specific phase of the cell cycle is under the control of various factors. Since the cell cycle in multicellular eukaryotes responds to multiple extracellular mitogenic cues, its study in higher forms of life becomes all the more important. One such factor regulating cell cycle progression in plants is sugar signalling. Because the growth of organs depends on both cell growth and proliferation, sugars sensing and signalling are key control points linking sugar perception to regulation of downstream factors which facilitate these key developmental transitions. However, the basis of cell cycle control via sugars is intricate and demands exploration. This review deals with the information on sugar and TOR-SnRK1 signalling and how they manoeuvre various events of the cell cycle to ensure proper growth and development.

Complex genetic interaction between glucose sensor HXK1 and E3 SUMO ligase SIZ1 in regulating plant morphogenesis.

Sugar signaling forms the basis of metabolic activities crucial for an organism to perform essential life activities. In plants, sugars like glucose, mediate a wide range of physiological responses ranging from seed germination to cell senescence. This has led to the elucidation of cell signaling pathways involving glucose and its counterparts and the mechanism of how these sugars take control over major hormonal pathways such as auxin, ethylene, abscisic acid and cytokinin in Arabidopsis. Plants use HXK1(Hexokinase) as a glucose sensor to modulate changes in photosynthetic gene expression in response to high glucose levels. Other proteins such as SIZ1, a major SUMO E3 ligase have recently been implicated in controlling sugar responses via transcriptional and translational regulation of a wide array of sugar metabolic genes. Here, we show that these two genes work antagonistically and are epistatic in controlling responsiveness toward high glucose conditions.

Hypocotyl directional growth in Arabidopsis: a complex trait.

The growth direction of the Arabidopsis (Arabidopsis thaliana) etiolated-seedling hypocotyl is a complex trait that is controlled by extrinsic signals such as gravity and touch as well as intrinsic signals such as hormones (brassinosteroid [BR], auxin, cytokinin, ethylene) and nutrient status (glucose [Glc], sucrose). We used a genetic approach to identify the signaling elements and their relationship underlying hypocotyl growth direction. BR randomizes etiolated-seedling growth by inhibiting negative gravitropism of the hypocotyls via modulating auxin homeostasis for which we designate as reset, not to be confused with the gravity set point angle. Cytokinin signaling antagonizes this BR reset of gravity sensing and/or tropism by affecting ethylene biosynthesis/signaling. Glc also antagonizes BR reset but acts independently of cytokinin and ethylene signaling pathways via inhibiting BR-regulated gene expression quantitatively and spatially, by altering protein degradation, and by antagonizing BR-induced changes in microtubule organization and cell patterning associated with hypocotyl agravitropism. This BR reset is reduced in the presence of the microtubule organization inhibitor oryzalin, suggesting a central role for cytoskeleton reorganization. A unifying and hierarchical model of Glc and hormone signaling interplay is proposed. The biological significance of BR-mediated changes in hypocotyl graviresponse lies in the fact that BR signaling sensitizes the dark-grown seedling hypocotyl to the presence of obstacles, overriding gravitropism, to enable efficient circumnavigation through soil.

Vapyrin, a gene essential for intracellular progression of arbuscular mycorrhizal symbiosis, is also essential for infection by rhizobia in the nodule symbiosis of Medicago truncatula.

Intracellular invasion of root cells is required for the establishment of successful endosymbioses in legumes of both arbuscular mycorrhizal (AM) fungi and rhizobial bacteria. In both interactions a requirement for successful entry is the activation of a common signalling pathway that includes five genes required to generate calcium oscillations and two genes required for the perception of the calcium response. Recently, it has been discovered that in Medicago truncatula, the Vapyrin (VPY) gene is essential for the establishment of the arbuscular mycorrhizal symbiosis. Here, we show by analyses of mutants that the same gene is also required for rhizobial colonization and nodulation. VPY encodes a protein featuring a Major Sperm Protein domain, typically featured on proteins involved in membrane trafficking and biogenesis, and a series of ankyrin repeats. Plants mutated in this gene have abnormal rhizobial infection threads and fewer nodules, and in the case of interactions with AM fungi, epidermal penetration defects and aborted arbuscule formation. Calcium spiking in root hairs in response to supplied Nod factors is intact in the vpy-1 mutant. This, and the elevation of VPY transcripts upon application of Nod factors which we show to be dependent on NFP, DMI1, and DMI3, indicates that VPY acts downstream of the common signalling pathway.