Abscisic Acid Signaling Components Research Articles

Interplay of Light and ABA signaling to modulate plant development.

The exogenous light cues and the phytohormone Abscisic acid (ABA) regulate several aspects of plant growth and development. In recent years, the role of the crosstalk between the light and ABA signaling pathways in regulating different physiological processes has become increasingly evident. This includes the regulation of germination and early seedling development, control of stomatal development and conductance, growth and development of roots, buds, branches, and regulation of flowering. Light and ABA signaling cascades have various convergence points at both DNA and protein levels. The molecular crosstalk involves several light signaling factors like HY5, COP1, PIFs and BBXs that integrate with ABA signaling components like the PYL receptors and ABI5. Especially, ABI5 and PIF4 promoters serve as key "hotspots" for the integration of these two pathways. Plants acquired both light and ABA signaling pathways before they colonized land almost 500 million years ago. In this review, we discuss the recent advances in the interplay of light and ABA signaling regulating plant development and provide an overview of the evolution of these two pathways.

MePP2C24, a cassava (Manihot esculenta) gene encoding protein phosphatase 2C, negatively regulates drought stress and abscisic acid responses in transgenic Arabidopsis thaliana

Abscisic acid (ABA) signaling plays a crucial role in plant development and response to abiotic/biotic stress. However, the function and regulation of protein phosphatase 2C (PP2C), a key component of abscisic acid signaling, under abiotic stress are still unknown in cassava, a drought-tolerant crop. In this study, a cassava PP2C gene (MePP2C24) was cloned and characterized. The MePP2C24 transcripts increased in response to mannitol, NaCl, and ABA. Overexpression of MePP2C24 in Arabidopsis resulted in increased sensitivity to drought stress and decreased sensitivity to exogenous ABA. This was demonstrated by transgenic lines having higher levels of malondialdehyde (MDA), ion leakage (IL), and reactive oxygen species (ROS), lower activities of catalase (CAT) and peroxidase (POD), and lower proline content than wild type (WT) under drought stress. Moreover, MePP2C24 overexpression caused decrease in expression of drought-responsive genes related to ABA signaling pathway. In addition, MePP2C24 was localized in the cell nucleus and showed self-activation. Furthermore, many MePYLs (MePYL1, MePYL4, MePYL7-9, and MePYL11-13) could interact with MePP2C24 in the presence of ABA, and MePYL1 interacted with MePP2C24 in both the presence and absence of ABA. Additionally, MebZIP11 interacted with the promoter of MePP2C24 and exerted a suppressive effect. Taken together, our results suggest that MePP2C24 acts as a negative regulator of drought tolerance and ABA response.

Mitochondrial VOLTAGE-DEPENDENT ANION CHANNEL 3 regulates stomatal closure by abscisic acid signaling.

In Arabidopsis (Arabidopsis thaliana), stomatal closure mediated by abscisic acid (ABA) is redundantly controlled by ABA receptor family proteins (PYRABACTIN RESISTANCE 1 [PYR1]/PYR1-LIKE [PYLs]) and subclass III SUCROSE NONFERMENTING 1 (SNF1)-RELATED PROTEIN KINASES 2 (SnRK2s). Among these proteins, the roles of PYR1, PYL2, and SnRK2.6 are more dominant. A recent discovery showed that ABA-induced accumulation of reactive oxygen species (ROS) in mitochondria promotes stomatal closure. By analyzing stomatal movements in an array of single and higher order mutants, we revealed that the mitochondrial protein VOLTAGE-DEPENDENT ANION CHANNEL 3 (VDAC3) jointly regulates ABA-mediated stomatal closure with a specialized set of PYLs and SnRK2s by affecting cellular and mitochondrial ROS accumulation. VDAC3 interacted with 9 PYLs and all 3 subclass III SnRK2s. Single mutation in VDAC3, PYLs (except PYR1 and PYL2), or SnRK2.2/2.3 had little effect on ABA-mediated stomatal closure. However, knocking out PYR1, PYL1/2/4/8, or SnRK2.2/2.3 in vdac3 mutants resulted in significantly delayed or attenuated ABA-mediated stomatal closure, despite the presence of other PYLs or SnRK2s conferring redundant functions. We found that cellular and mitochondrial accumulation of ROS induced by ABA was altered in vdac3pyl1 mutants. Moreover, H2O2 treatment restored ABA-induced stomatal closure in mutants with decreased stomatal sensitivity to ABA. Our work reveals that VDAC3 ensures redundant control of ABA-mediated stomatal closure by canonical ABA signaling components.

Suspension Trapping-Based Sample Preparation Workflow for In-Depth Plant Phosphoproteomics.

Plant phosphoproteomics provides a global view of phosphorylation-mediated signaling in plants; however, it demands high-throughput methods with sensitive detection and accurate quantification. Despite the widespread use of protein precipitation for removing contaminants and improving sample purity, it limits the sensitivity and throughput of plant phosphoproteomic analysis. The multiple handling steps involved in protein precipitation lead to sample loss and process variability. Herein, we developed an approach based on suspension trapping (S-Trap), termed tandem S-Trap-IMAC (immobilized metal ion affinity chromatography), by integrating an S-Trap micro-column with a Fe-IMAC tip. Compared with a precipitation-based workflow, the tandem S-Trap-IMAC method deepened the coverage of the Arabidopsis (Arabidopsis thaliana) phosphoproteome by more than 30%, with improved number of multiply phosphorylated peptides, quantification accuracy, and short sample processing time. We applied the tandem S-Trap-IMAC method for studying abscisic acid (ABA) signaling in Arabidopsis seedlings. We thus discovered that a significant proportion of the phosphopeptides induced by ABA are multiply phosphorylated peptides, indicating their importance in early ABA signaling and quantified several key phosphorylation sites on core ABA signaling components across four time points. Our results show that the optimized workflow aids high-throughput phosphoproteome profiling of low-input plant samples.

Identification of Pyrabactin resistance 1-like (PYL) genes in Brachypodium distachyon and functional characterization of BdPYL5

Abscisic acid (ABA) is an endogenous phytohormone that plays an important role in regulating plant growth, development, and stress response. Pyrabactin resistance 1-like (PYR/PYL) proteins are ABA receptors and core components of ABA signalling in plants. This study identified nine PYL genes in the Brachypodium distachyon genome and they distribute on three chromosomes. Phylogenetical BdPYLs were classified into three clades. 81 protein-protein interactions between 9 BdPYLs and 9 BdPP2C proteins were predicted and 66 pairs were verified by yeast two-hybrid assay previously. Relatively, BdPYL genes are expressed in leaves at high level, and ABA and drought regulate their expression. A homologue of Arabidopsis PYL9, BdPYL5 was selected to overexpress in Arabidopsis to characterize its function. In general, overexpression of BdPYL5 enhanced ABA sensitivity and drought tolerance, implying its conserved function. Our study lays the foundation for further functional elucidation of BdPYL genes.

The OPEN STOMATA1-SPIRAL1 module regulates microtubule stability during abscisic acid-induced stomatal closure in Arabidopsis.

Drought stress triggers abscisic acid (ABA) signaling in guard cells and induces stomatal closure to prevent water loss in land plants. Stomatal movement is accompanied by reorganization of the cytoskeleton. Cortical microtubules disassemble in response to ABA, which is required for stomatal closure. However, how ABA signaling regulates microtubule disassembly is unclear, and the microtubule-associated proteins (MAPs) involved in this process remain to be identified. In this study, we show that OPEN STOMATA 1 (OST1), a central component in ABA signaling, mediates microtubule disassembly during ABA-induced stomatal closure in Arabidopsis thaliana. We identified the MAP SPIRAL1 (SPR1) as the substrate of OST1. OST1 interacts with and phosphorylates SPR1 at Ser6, which promotes the disassociation of SPR1 from microtubules and facilitates microtubule disassembly. Compared with the wild type, the spr1 mutant exhibited significantly greater water loss and reduced ABA responses, including stomatal closure and microtubule disassembly in guard cells. These phenotypes were restored by introducing the phosphorylated active form of SPR1. Our findings demonstrate that SPR1 positively regulates microtubule disassembly during ABA-induced stomatal closure, which depends on OST1-mediated phosphorylation. These findings reveal a specific connection between a core component of ABA signaling and MAPs.

Malate induces stomatal closure via a receptor-like kinase GHR1- and reactive oxygen species-dependent pathway in Arabidopsis thaliana.

A primary metabolite malate is secreted from guard cells in response to the phytohormone abscisic acid (ABA) and elevated CO2. The secreted malate subsequently facilitates stomatal closure in plants. Here, we investigated the molecular mechanism of malate-induced stomatal closure using inhibitors and ABA signaling component mutants of Arabidopsis thaliana. Malate-induced stomatal closure was impaired by a protein kinase inhibitor, K252a, and also by the disruption of a receptor-like kinase GHR1, which mediates activation of calcium ion (Ca2+) channel by reactive oxygen species (ROS) in guard cells. Malate induced ROS production in guard cells while the malate-induced stomatal closure was impaired by a peroxidase inhibitor, salicylhydroxamic acid, but not by the disruption of Nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidases, RBOHD and RBOHF. The malate-induced stomatal closure was impaired by Ca2+ channel blockers, verapamil, and niflumic acid. These results demonstrate that the malate signaling is mediated by GHR1 and ROS in Arabidopsis guard cells.

ABI3- and PIF1-mediated regulation of GIG1 enhances seed germination by detoxification of methylglyoxal in Arabidopsis.

Methylglyoxal (MG) is a toxic by-product of the glycolysis pathway in most living organisms and was previously shown to inhibit seed germination. MG is detoxified by glyoxalase I and II family proteins in plants. MG is abundantly produced during early embryogenesis in Arabidopsis seeds. However, the mechanism that alleviates the toxic effect of MG in maturing seeds is poorly understood. In this study, by T-DNA mutant population screening, we found that mutations in a glyoxalase I gene (named GERMINATION-IMPAIRED GLYOXALASE 1, GIG1) led to significantly impaired germination compared with wild-type seeds. Transformation of full-length GIG1 cDNA under the constitutively active cauliflower mosaic virus 35S promoter in the gig1 background completely recovered the seed germination phenotype. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analyses revealed that GIG1 is uniquely expressed in seeds and is upregulated by abscisic acid (ABA) and downregulated by gibberellic acid (GA) during seed germination. An ABA signaling component, ABI3, directly activated GIG1 in maturing seeds. In addition, PHYTOCHROME INTERACTING FACTOR 1 (PIF1) also plays cooperatively with ABI3 in the regulation of GIG1 expression in the early stage of imbibed seeds. Furthermore, GIG1 expression is stably silenced by epigenetic repressors such as polycomb repressor complexes. Altogether, our results indicate that light and ABA signaling cooperate to enhance seed germination by the upregulation of GIG1 to detoxify MG in maturing seeds.

Molecular and physiological responses to desiccation indicate the abscisic acid pathway is conserved in the peat moss, Sphagnum.

Mosses of the genus Sphagnum are the main components of peatlands, a major carbon-storing ecosystem. Changes in precipitation patterns are predicted to affect water relations in this ecosystem, but the effect of desiccation on the physiological and molecular processes in Sphagnum is still largely unexplored. Here we show that different Sphagnum species have differential physiological and molecular responses to desiccation but, surprisingly, this is not directly correlated with their position in relation to the water table. In addition, the expression of drought responsive genes is increased upon water withdrawal in all species. This increase in gene expression is accompanied by an increase in abscisic acid (ABA), supporting a role for ABA during desiccation responses in Sphagnum. Not only do ABA levels increase upon desiccation, but Sphagnum plants pre-treated with ABA display increased tolerance to desiccation, suggesting that ABA levels play a functional role in the response. In addition, many of the ABA signalling components are present in Sphagnum and we demonstrate, by complementation in Physcomitrium patens, that Sphagnum ABI3 is functionally conserved. The data presented here, therefore, support a conserved role for ABA in desiccation responses in Sphagnum.

Affinity Purification Followed by Liquid Chromatography-Tandem Mass Spectrometry to Identify Proteins Interacting with ABA Signaling Components.

Abscisic acid (ABA) is a key phytohormone involved in plant development, seed germination and responses to osmotic stresses, such as drought and high salinity. SNF1-related protein kinases (SnRK2s) play important roles in ABA-dependent and ABA-independent osmotic stress signaling. SnRK2s phosphorylate transcription factors and ion channels in response to ABA or osmotic stress to induce the expression of stress-responsive genes and stomatal closure, respectively, to confer osmotic stress tolerance. The activity of SnRK2s is directly or indirectly regulated by several protein factors. Identification of downstream substrates or upstream regulators of SnRK2s is very useful for elucidating protein components that regulate ABA and osmotic stress signaling. Here, we describe the use of affinity purification by coimmunoprecipitation and liquid chromatography-tandem mass spectrometry to identify protein complexes involved in ABA and osmotic stress signaling in plants. We previously identified several protein factors that regulate ABA and osmotic stress signaling by using this method.

Conditional stomatal closure in a fern shares molecular features with flowering plant active stomatal responses

Stomata evolved as plants transitioned from water to land, enabling carbon dioxide uptake and water loss to be controlled. In flowering plants, the most recently divergent land plant lineage, stomatal pores actively close in response to drought. In this response, the phytohormone abscisic acid (ABA) triggers signaling cascades that lead to ion and water loss in the guard cells of the stomatal complex, causing a reduction in turgor and pore closure. Whether this stimulus-response coupling pathway acts in other major land plant lineages is unclear, with some investigations reporting that stomatal closure involves ABA but others concluding that closure is passive. Here, we show that in the model fern Ceratopteris richardii active stomatal closure is conditional on sensitization by pre-exposure to either low humidity or exogenous ABA and is promoted by ABA. RNA-seq analysis and de novo transcriptome assembly reconstructed the protein-coding complement of the C.richardii genome, with coverage comparable to other plant models, enabling transcriptional signatures of stomatal sensitization and closure to be inferred. In both cases, changes in abundance of homologs of ABA, Ca2+, and ROS-related signaling components were observed, suggesting that the closure-response pathway is conserved in ferns and flowering plants. These signatures further suggested that sensitization is achieved by lowering the threshold required for a subsequent closure-inducing signal to trigger a response. We conclude that the canonical signaling network for active stomatal closure functioned in at least a rudimentary form in the stomata of the last common ancestor of ferns and flowering plants.

CaADIP1‐dependent CaADIK1‐kinase activation is required for abscisic acid signalling and drought stress response in Capsicum annuum

Induction of the abscisic acid (ABA) signalling network is associated with various stress conditions, including cold, high salinity and drought. As core ABA signalling components, group A type 2C protein phosphatases (PP2Cs) interact with and inhibit snf1-related protein kinase2s. Here, we isolated and characterised the pepper mitogen-activated protein kinase kinase kinase CaADIK1, which interacts with the group A PP2C CaADIP1. CaADIK1 transcripts were induced by abiotic stresses, and CaADIK1 localised in the nucleus and cytoplasm. We verified that CaADIP1 inhibits the autokinase activity of CaADIK1; moreover, the kinase activity of CaADIK1 is enhanced by drought stress. We performed genetic analysis using CaADIK1-silenced pepper and CaADIK1-overexpressing (OX) Arabidopsis plants. CaADIK1-silenced pepper plants showed drought-sensitive phenotypes, whereas CaADIK1-OX Arabidopsis plants showed ABA-sensitive and drought-tolerant phenotypes. In CaADIK1K32N -OX Arabidopsis plants mutated at the ATP-binding site, the ABA-insensitive and drought-sensitive phenotypes were restored. Taken together, our findings show that CaADIK1 positively regulates the ABA-dependent drought stress response and is inhibited by CaADIP1.

SnRK2.6 interacts with phytochrome B and plays a negative role in red light-induced stomatal opening

ABSTRACT Light is an important environmental factor for plant growth and development. Phytochrome B (phyB), a classical red/far-red light receptor, plays vital role in controlling plant photomorphogenesis and light-induced stomatal opening. Phytohormone abscisic acid (ABA) accumulates rapidly and triggers a series of physiological and molecular events during the responses to multiple abiotic stresses. Recent studies showed that phyB mutant synthesizes more ABA and exhibits improved tolerance to salt and cold stress, suggesting that a crosstalk exists between light and ABA signaling pathway. However, whether ABA signaling components mediate responses to light remains unclear. Here, we showed that SnRK2.6 (Sucrose Nonfermenting 1-Related Protein Kinase 2.6), a key regulator in ABA signaling, interacts with phyB and participates in light-induced stomatal opening. First, we checked the interaction between phyB and SnRK2s, and found that SnRK2.2/2.3/2.6 kinases physically interacted with phyB in yeast and in vitro. We also performed co-IP assay to support that SnRK2.6 interacts with phyB in plant. To investigate the role of SnRK2.6 in red light-induced stomatal opening, we obtained the snrk2.6 mutant and overexpression lines, and found that snrk2.6 mutant exhibited a significantly larger stomatal aperture under red light treatment, while the two independent overexpression lines showed significantly smaller stomatal aperture, indicative of a negative role for SnRK2.6 in red light-induced stomatal opening. The interaction of SnRK2.6 with red light receptor and the negative role of SnRK2.6 in red light-induced stomatal opening provide new evidence for the crosstalk between ABA and red light in guard cell signaling.

Abscisic acid signaling negatively regulates nitrate uptake via phosphorylation of NRT1.1 by SnRK2s in Arabidopsis.

Nitrogen (N) is a limiting nutrient for plant growth and productivity. The phytohormone abscisic acid (ABA) has been suggested to play a vital role in nitrate uptake in fluctuating N environments. However, the molecular mechanisms underlying the involvement of ABA in N deficiency responses are largely unknown. In this study, we demonstrated that ABA signaling components, particularly the three subclass III SUCROSE NON-FERMENTING1 (SNF1)-RELATED PROTEIN KINASE 2S (SnRK2) proteins, function in root foraging and uptake of nitrate under N deficiency in Arabidopsis thaliana. The snrk2.2snrk2.3snrk2.6 triple mutant grew a longer primary root and had a higher rate of nitrate influx and accumulation compared with wild-type plants under nitrate deficiency. Strikingly, SnRK2.2/2.3/2.6 proteins interacted with and phosphorylated the nitrate transceptor NITRATE TRANSPORTER1.1 (NRT1.1) in vitro and in vivo. The phosphorylation of NRT1.1 by SnRK2s resulted in a significant decrease of nitrate uptake and impairment of root growth. Moreover, we identified NRT1.1Ser585 as a previously unknown functional site: the phosphomimetic NRT1.1S585D was impaired in both low- and high-affinity transport activities. Taken together, our findings provide new insight into how plants fine-tune growth via ABA signaling under N deficiency.

AITRL, an evolutionarily conserved plant specific transcription repressor regulates ABA response in Arabidopsis

Expression of stress response genes can be regulated by abscisic acid (ABA) dependent and ABA independent pathways. Osmotic stresses promote ABA accumulation, therefore inducing the expression of stress response genes via ABA signaling. Whereas cold and heat stresses induce the expression of stress response genes via ABA independent pathway. ABA induced transcription repressors (AITRs) are a family of novel transcription factors that play a role in ABA signaling, and Drought response gene (DRG) has previously been shown to play a role in regulating plant response to drought and freezing stresses. We report here the identification of DRG as a novel transcription factor and a regulator of ABA response in Arabidopsis. We found that the expression of DRG was induced by ABA treatment. Homologs searching identified AITR5 as the most closely related Arabidopsis protein to DRG, and homologs of DRG, including the AITR-like (AITRL) proteins in bryophytes and gymnosperms, are specifically presented in embryophytes. Therefore we renamed DRG as AITRL. Protoplast transfection assays show that AITRL functioned as a transcription repressor. In seed germination and seedling greening assays, the aitrl mutants showed an increased sensitivity to ABA. By using qRT-PCR, we show that ABA responses of some ABA signaling component genes including some PYR1-likes (PYLs), PROTEIN PHOSPHATASE 2Cs (PP2Cs) and SUCROSE NONFERMENTING 1 (SNF1)-RELATED PROTEIN KINASES 2s (SnRK2s) were reduced in the aitrl mutants. Taken together, our results suggest that AITRLs are a family of novel transcription repressors evolutionally conserved in embryophytes, and AITRL regulates ABA response in Arabidopsis by affecting ABA response of some ABA signaling component genes.

COP1 promotes ABA-induced stomatal closure by modulating the abundance of ABI/HAB and AHG3 phosphatases.

Summary Plant stomata play a crucial role in leaf function, controlling water transpiration in response to environmental stresses and modulating the gas exchange necessary for photosynthesis. The phytohormone abscisic acid (ABA) promotes stomatal closure and inhibits light‐induced stomatal opening. The Arabidopsis thaliana E3 ubiquitin ligase COP1 functions in ABA‐mediated stomatal closure. However, the underlying molecular mechanisms are still not fully understood.Yeast two‐hybrid assays were used to identify ABA signaling components that interact with COP1, and biochemical, molecular and genetic studies were carried out to elucidate the regulatory role of COP1 in ABA signaling.The cop1 mutants are hyposensitive to ABA‐triggered stomatal closure under light and dark conditions. COP1 interacts with and ubiquitinates the Arabidopsis clade A type 2C phosphatases (PP2Cs) ABI/HAB group and AHG3, thus triggering their degradation. Abscisic acid enhances the COP1‐mediated degradation of these PP2Cs. Mutations in ABI1 and AHG3 partly rescue the cop1 stomatal phenotype and the phosphorylation level of OST1, a crucial SnRK2‐type kinase in ABA signaling.Our data indicate that COP1 is part of a novel signaling pathway promoting ABA‐mediated stomatal closure by regulating the stability of a subset of the Clade A PP2Cs. These findings provide novel insights into the interplay between ABA and the light signaling component in the modulation of stomatal movement.

Interactions between calcium and ABA signaling pathways in the regulation of fruit ripening

Fruit ripening and senescence are finely controlled by plant hormones such as ethylene and abscisic acid (ABA) but also by calcium ions and by calcium-dependent signaling pathways. Although there are extensive data supporting an interaction between ethylene and calcium in fruit ripening, the regulatory mechanisms resulting from the interaction between ABA and calcium have not yet been fully clarified. In this article, we have reviewed the full roles of calcium and its sensors (CaM, CMLs, CDPKs, CBLs) as well as ABA and the interactions between the two signaling pathways in the regulation of stress responses and in fruit ripening. To illustrate the possible interaction between calcium sensors and ABA signaling components in the control of fruit ripening, we propose an interaction model between the calcium and ABA signaling pathways.

Light and abscisic acid interplay in early seedling development.

Abscisic acid (ABA) plays a crucial role in plant development, regulating germination, seedling development and stomatal movements, especially under adverse conditions. Light interacts with the ABA signalling pathway to fine tune these processes. Here, we provide an overview of the recent investigations on ABA-light interplay during early plant development after germination. We discuss the multilayered and reciprocal interactions between ABA signalling components and several light signalling modulators, including photoreceptors, transcription factors and posttranslational modifiers. ABSCISIC ACID INSENSITIVE5 acts as a central convergence point for these interactions during postgermination seedling development. ABA also regulates the adaptation of seedlings to challenging light environments. Furthermore, we enlist the role of ABA-light cross-talk in regulating seedling establishment in crops and highlight open questions for future investigations.

A dual function of SnRK2 kinases in the regulation of SnRK1 and plant growth

Adverse environmental conditions trigger responses in plants that promote stress tolerance and survival at the expense of growth1. However, little is known of how stress signalling pathways interact with each other and with growth regulatory components to balance growth and stress responses. Here, we show that plant growth is largely regulated by the interplay between the evolutionarily conserved energy-sensing SNF1-related protein kinase 1 (SnRK1) protein kinase and the abscisic acid (ABA) phytohormone pathway. While SnRK2 kinases are main drivers of ABA-triggered stress responses, we uncover an unexpected growth-promoting function of these kinases in the absence of ABA as repressors of SnRK1. Sequestration of SnRK1 by SnRK2-containing complexes inhibits SnRK1 signalling, thereby allowing target of rapamycin (TOR) activity and growth under optimal conditions. On the other hand, these complexes are essential for releasing and activating SnRK1 in response to ABA, leading to the inhibition of TOR and growth under stress. This dual regulation of SnRK1 by SnRK2 kinases couples growth control with environmental factors typical for the terrestrial habitat and is likely to have been critical for the water-to-land transition of plants.

Decoding ABA and osmostress signalling in plants from an evolutionary point of view.

The plant hormone abscisic acid (ABA) is fundamental for land plant adaptation to water-limited conditions. Osmostress, such as drought, induces ABA accumulation in angiosperms, triggering physiological responses such as stomata closure. The core components of angiosperm ABA signalling are soluble ABA receptors, group A protein phosphatase type 2C and SNF1-related protein kinase2 (SnRK2). ABA also has various functions in non-angiosperms, however, suggesting that its role in adaptation to land may not have been angiosperm-specific. Indeed, among land plants, the core ABA signalling components are evolutionarily conserved, implying their presence in a common ancestor. Results of ongoing functional genomics studies of ABA signalling components in bryophytes and algae have expanded our understanding of the evolutionary role of ABA signalling, with genome sequencing uncovering the ABA core module even in algae. In this review, we describe recent discoveries involving the ABA core module in non-angiosperms, tracing the footprints of how ABA evolved as a phytohormone. We also cover the latest findings on Raf-like kinases as upstream regulators of the core ABA module component SnRK2. Finally, we discuss the origin of ABA signalling from an evolutionary perspective.