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Both seed germination and subsequent seedling establishment are key checkpoints during the life cycle of seed plants, yet flooding stress markedly inhibits both processes, leading to economic losses from agricultural production. Here, we report that melatonin (MT) seed priming treatment enhances the performance of seeds from several crops, including soybean, wheat, maize, and alfalfa, under flooding stress. Transcriptome analysis revealed that MT priming promotes seed germination and seedling establishment associated with changes in abscisic acid (ABA), gibberellin (GA), and reactive oxygen species (ROS) biosynthesis and signaling pathways. Real-time quantitative RT-PCR (qRT-PCR) analysis confirmed that MT priming increases the expression levels of GA biosynthesis genes, ABA catabolism genes, and ROS biosynthesis genes while decreasing the expression of positive ABA regulatory genes. Further, measurements of ABA and GA concentrations are consistent with these trends. Following MT priming, quantification of ROS metabolism-related enzyme activities and the concentrations of H 2 O 2 and superoxide anions (O 2 - ) after MT priming were consistent with the results of transcriptome analysis and qRT-PCR. Finally, exogenous application of GA, fluridone (an ABA biosynthesis inhibitor), or H 2 O 2 partially rescued the poor germination of non-primed seeds under flooding stress. Collectively, this study uncovers the application and molecular mechanisms underlying MT priming in modulating crop seed vigor under flooding stress., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Transcriptional regulation plays a key role in the control of seed dormancy, and many transcription factors (TFs) have been documented. However, the mechanisms underlying the interactions between different TFs within a transcriptional complex regulating seed dormancy remain largely unknown. Here, we showed that TF PHYTOCHROME-INTERACTING FACTOR4 (PIF4) physically interacted with the abscisic acid (ABA) signaling responsive TF ABSCISIC ACID INSENSITIVE4 (ABI4) to act as a transcriptional complex to promote ABA biosynthesis and signaling, finally deepening primary seed dormancy. Both pif4 and abi4 single mutants exhibited a decreased primary seed dormancy phenotype, with a synergistic effect in the pif4/abi4 double mutant. PIF4 binds to ABI4 to form a heterodimer, and ABI4 stabilizes PIF4 at the protein level, whereas PIF4 does not affect the protein stabilization of ABI4. Subsequently, both TFs independently and synergistically promoted the expression of ABI4 and NCED6, a key gene for ABA anabolism. The genetic evidence is also consistent with the phenotypic, physiological and biochemical analysis results. Altogether, this study revealed a transcriptional regulatory cascade in which the PIF4-ABI4 transcriptional activator complex synergistically enhanced seed dormancy by facilitating ABA biosynthesis and signaling., (© 2024 Institute of Botany, Chinese Academy of Sciences.)

Although ABSCISIC ACID INSENSITIVE 4 (ABI4) was initially demonstrated as a key positive regulator in the phytohormone abscisic acid (ABA) signaling cascade, multiple studies have now shown that it is actually involved in the regulation of several other cascades, including diverse phytohormone biogenesis and signaling pathways, various developmental processes (such as seed dormancy and germination, seedling establishment, and root development), disease resistance and lipid metabolism. Consistent with its versatile biological functions, ABI4 either activates or represses transcription of its target genes. The upstream regulators of ABI4 at both the transcription and post-transcription levels have also been documented in recent years. Consequently, a complicated network consisting of the direct target genes and upstream regulators of ABI4, through which ABI4 participates in several phytohormone crosstalk networks, has been generated. In this review, we summarize current understanding of the sophisticated ABI4-mediated molecular networks, mainly focusing on diverse phytohormone (including ABA, gibberellin, cytokinin, ethylene, auxin, and jasmonic acid) crosstalks. We also discuss the potential mechanisms through which ABI4 receives the ABA signal, focusing on protein phosphorylation modification events., (© 2020 The Author(s).)

Emerging evidence suggests that the stress hormone abscisic acid (ABA) is also involved in the floral transition control. The transcription factors ABA INSENSITIVE4 (ABI4) and ABI5 negatively regulate flowering by directly promoting FLOWERING LOCUS C expression, and ABI3 also negatively regulates the floral transition. However, the genetic relationships between ABI4 and both ABI5 and ABI3 remain elusive. Here, we generated transgenic plants overexpressing ABI4 in the abi5 (OE-ABI4::abi5) and abi3 backgrounds (OE-ABI4::abi3). The flowering phenotypic analysis demonstrated that OE-ABI4::abi5 and OE-ABI4::abi3 plants exhibited delayed flowering. These findings suggest that ABI4 independently regulates floral transition but not through ABI5 and ABI3 cascades.

The transition from the vegetative growth phase to flowering is a crucial checkpoint for plant reproduction and survival, especially under environmental stress conditions. Numerous factors regulate flowering time, including exogenous environmental cues such as day length and temperature, as well as salt and drought stresses, and endogenous phytohormone signaling cascades. Gibberellins and ABA are one classic combination of phytohormones which antagonistically regulate several biological processes, including seed dormancy and germination, primary root growth and seedling development. As regards control of flowering time, gibberellin exhibits a positive role, and represents an important pathway in the regulation of floral transition. However, over the past decades, numerous investigations have demonstrated that the contribution of the stress hormone ABA to floral transition is still controversial, as both positive and negative effects have been documented. It is important to determine why and how ABA shows this contradictory effect on flowering time. In this up to date review, primarily based on recent publications and emerging data, we summarize the distinct and contrasting roles of ABA on floral transition, while the detailed molecular mechanisms underlying these roles are discussed. Finally, the remaining challenges and open questions in this topic are presented.

Karrikins (KAR) are a class of signal compounds, discovered in wildfire smoke, which affect seed germination. Currently, numerous studies have focused on the model plant Arabidopsis in the KAR research field, rather than on crops. Thus the regulatory mechanisms underlying KAR regulation of crop seed germination are largely unknown. Here, we report that KAR delayed soybean seed germination through enhancing abscisic acid (ABA) biosynthesis, while impairing gibberellin (GA) biogenesis. Interestingly, KAR only retarded soybean seed germination under shaded conditions, rather than under dark and white light conditions, which differs from in Arabidopsis. Phytohormone quantification showed that KAR enhanced ABA biogenesis while impairing GA biosynthesis during the seed imbibition process, and subsequently, the ratio of active GA4 to ABA was significantly reduced. Further qRT-PCR analysis showed that the transcription pattern of genes involved in ABA and GA metabolic pathways are consistent with the hormonal measurements. Finally, fluridone, an ABA biogenesis inhibitor, remarkably rescued the delayed-germination phenotype of KAR-treatment; and paclobutrazol, a GA biosynthesis inhibitor, inhibited soybean seed germination. Taken together, these evidences suggest that KAR inhibit soybean seed germination by mediating the ratio between GA and ABA biogenesis.

Summary: Abscisic acid (ABA) and gibberellins (GA) antagonistically mediate several biological processes, including seed germination, but the molecular mechanisms underlying ABA/GA antagonism need further investigation, particularly any role mediated by a transcription factors module.Here, we report that the DELLA protein RGL2, a repressor of GA signaling, specifically interacts with ABI4, an ABA signaling enhancer, to act as a transcription factor complex to mediate ABA/GA antagonism.The rgl2, abi3, abi4 and abi5 mutants rescue the non‐germination phenotype of the ga1‐t. Further, we demonstrate that RGL2 specifically interacts with ABI4 to form a heterodimer. RGL2 and ABI4 stabilize one another, and GA increases the ABI4‐RGL2 module turnover, whereas ABA decreases it. At the transcriptional level, ABI4 enhances the RGL2 expression by directly binding to its promoter via the CCAC cis‐element, and RGL2 significantly upregulates the transcriptional activation ability of ABI4 toward its target genes, including ABI5 and RGL2. Abscisic acid promotes whereas GA inhibits the ability of ABI4‐RGL2 module to activate transcription, and ultimately ABA and GA antagonize each other. Genetic analysis demonstrated that both ABI4 and RGL2 are essential for the activity of this transcription factor module.These results suggest that the ABI4‐RGL2 module mediates ABA/GA antagonism by functioning as a double agent. [ABSTRACT FROM AUTHOR]

Appropriate timing of seed germination is crucial for plant survival and has important implications for agricultural production. Timely germination relies on harmonious interactions between endogenous developmental signals, especially abscisic acid (ABA) and gibberellins (GAs), and environmental cues such as light. Recently, a series of investigations of a three-way crosstalk between phytochromes, ABA, and GAs in the regulation of seed germination demonstrated that the transcription factor ABSCISIC ACID INSENSITIVE 5 (ABI5) is a central mediator in the light–ABA/GA cascades. Here, we review current knowledge of ABI5 as a key player in light-, ABA-, and GA-signaling pathways that precisely control seed germination. We highlight recent advances in ABI5-related studies, focusing on the regulation of seed germination, which is strictly controlled at both the transcriptional and the protein levels by numerous light-regulated factors. We further discuss the components of ABA and GA signaling pathways that could regulate ABI5 during seed germination, including transcription factors, E3 ligases, protein kinases, and phosphatases. The precise molecular mechanisms by which ABI5 mediates ABA–GA antagonistic crosstalk during seed germination are also discussed. Finally, some potential research hotspots underlying ABI5-mediated seed germination regulatory networks are proposed. [ABSTRACT FROM AUTHOR]

It is noted that the other important phytohormone auxin plays key roles in seed dormancy and germination control (Liu et al., [20]), thus the molecular mechanisms of auxin in regulating seed germination after parental shading need to be further explored. Keywords: gibberellic acid; abscisic acid; seed germination; phytohormone; parental shading EN gibberellic acid abscisic acid seed germination phytohormone parental shading 1 4 4 11/12/21 20211108 NES 211108 Introduction Seed germination is essential for subsequent young seedling establishment. R light enhances seed germination through inhibition of the expression of ABA biosynthesis genes, while FR light delays seed germination by promoting the transcription of ABA biosynthesis genes (Barrero et al., [3]). Furthermore, given the repression effects of pro-anthocyanidins in seed germination (Jia et al., [14]), parental shading treatment also downregulated the levels of soluble pro-anthocyanidins in developing seeds, which further enhanced subsequent seed germination (Chen et al., [6]). [Extracted from the article]

Ethylene positively regulates ABA catabolism and negatively regulates ABA biosynthesis, thereby affecting ABA content. During hypoxia stress, ABA biosynthesis is inhibited, while the catabolism cascade is enhanced, and thus, exogenous ABA can increase the tolerance of plants to hypoxia stress (Dawood et al., [8]; De Ollas et al., [9]). Keywords: ABA; hypoxia; submergence; waterlogging; flooding; ethylene EN ABA hypoxia submergence waterlogging flooding ethylene 1 6 6 06/28/21 20210624 NES 210624 Introduction Hypoxia is one of the major abiotic stresses, primarily caused by numerous flooding events such as waterlogging and submergence (Zhou et al., [56]; Xie et al., [48]), with deleterious effects on plant growth and development (Bailey-Serres et al., [4]; Voesenek and Bailey-Serres, [43]; Xie et al., [48]; Zhou et al., [58]). Abscisic Acid Biosynthesis Under Hypoxia Stress The abscisic acid level in internode meristem and cell elongation zone of submerged plants decreased by 75% in deepwater rice after flooding (Kende, [22]). [Extracted from the article]

Summary: Salinity stress enhances reactive oxygen species (ROS) accumulation by activating the transcription of NADPH oxidase genes such as RbohD, thus mediating plant developmental processes, including seed germination. However, how salinity triggers the expression of ROS‐metabolism‐related genes and represses seed germination has not yet been fully addressed.In this study, we show that Abscisic Acid‐Insensitive 4 (ABI4), a key component in abscisic acid (ABA) signaling, directly combines with RbohD and Vitamin C Defective 2 (VTC2), the key genes involved in ROS production and scavenging, to modulate ROS metabolism during seed germination under salinity stress.Salinity‐induced ABI4 enhances RbohD expression by physically interacting with its promoter, and subsequently promotes ROS accumulation, thus resulting in cell membrane damage and a decrease in seed vigor. Additional genetic evidence indicated that the rbohd mutant largely rescues the salt‐hypersensitive phenotype of ABI4 overexpression seeds. Consistently, the abi4/vtc2 double mutant showed the salt‐sensitive phenotype, similar to the vtc2 mutant, suggesting that both RbohD and VTC2 are epistatic to ABI4 genetically.Altogether, these results suggest that the salt‐induced RbohD transcription and ROS accumulation is dependent on ABI4, and that the ABI4‐RbohD/VTC2 regulatory module integrates both ROS metabolism and cell membrane integrity, ultimately repressing seed germination under salinity stress. [ABSTRACT FROM AUTHOR]

Keywords: seed germination; phytohormones; ROS; nanoparticle; seed priming; starch degradation EN seed germination phytohormones ROS nanoparticle seed priming starch degradation 1 6 6 06/12/20 20200610 NES 200610 Introduction Nanotechnology-driven smart agriculture has been considered as one of the highly potential approaches in improving crop productivity ([12]). Although nanoparticle based studies are fruitful in numerous fields over a decade, such as nanomedicine ([39]; [16]; [24]), nanoindustrial application ([33]), nanopharmacy ([17]) and nanopesticide ([34]; [21]), a higher advancement of nanoparticle based studies in releasing seed dormancy and enhancing seed germination as well as seedling development have recently come to the limelight in the form of seed-nanopriming technology. Conclusion and Future Prospects Overall, the link between nanoparticle adhesion and phytohormone crosstalk in influencing seed germination in a nanoprimed seed is only in the beginner's stage. Seed germination, phytohormones, ROS, nanoparticle, seed priming, starch degradation. [Extracted from the article]

The effect of shading during seed development on subsequent germination remains largely unknown. In this study, two soybean (Glycine max) seed production systems, monocropping (MC) and maize–soybean intercropping (IC), were employed to examine the effects of shading of the mother plant on subsequent seed germination. Compared to the MC soybean seeds, which received light, the developing IC seeds were exposed to shade resulting from the taller neighboring maize plants. The IC seeds germinated faster than the MC seeds, although there was no significant difference in the thickness of the seed coat. The concentration of soluble pro-anthocyanidin in the IC seed coat was significantly lower than that in the MC seed coat. Changes in the concentrations of several types of fatty acids in IC seeds were also observed, the nature of which were consistent with the effect on germination. The expression levels of genes involved in abscisic acid (ABA) biosynthesis were down-regulated in IC seeds, while the transcription levels of the genes related to gibberellin (GA) biosynthesis were up-regulated. This was consistently reflected in decreased ABA concentrations and increased active GA4 concentrations in IC seeds, resulting in an increased GA4/ABA ratio. Our results thus indicated that shading of the mother plant during seed development in soybean promoted subsequent germination by mediating the biosynthesis of pro-anthocyanidins, fatty acids, and phytohormones. [ABSTRACT FROM AUTHOR]

Phytohormones regulate numerous important biological processes in plant development and biotic/abiotic stress response cascades. More than 50 and 100 years have passed since the initial discoveries of the phytohormones abscisic acid (ABA) and gibberellins (GA), respectively. Over the past several decades, numerous elegant studies have demonstrated that ABA and GA antagonistically regulate many plant developmental processes, including seed maturation, seed dormancy and germination, root initiation, hypocotyl and stem elongation, and floral transition. Furthermore, as a well-established stress hormone, ABA plays a key role in plant responses to abiotic stresses, such as drought, flooding, salinity and low temperature. Interestingly, recent evidence revealed that GA are also involved in plant response to adverse environmental conditions. Consequently, the complex crosstalk networks between ABA and GA, mediated by diverse key regulators, have been extensively investigated and documented. In this updated mini-review, we summarize the most recent advances in our understanding of the antagonistically regulatory roles of ABA and GA in different stages of plant development and in various plant-environment interactions, focusing on the crosstalk between ABA and GA at the levels of phytohormone metabolism and signal transduction. [ABSTRACT FROM AUTHOR]

• Flooding reduces soybean seed germination by decreasing the catabolism from triacylglycerol to sugars. • Flooding stress upset the balance between ABA and GA during soybean seed germination. • Flooding stress promoting anaerobic respiration and the accumulation of ethanol. • The exogenous sucrose or GA treatments can partially rescue floods-mediated repression of seed germination. With global warming, flooding is becoming a serious natural abiotic stress in the past decades, which significantly influences plant growth and development, especially seed germination. However, the molecular mechanisms by which flooding stress represses land crop seed germination are largely unknown so far. Here, by using soybean (Glycine max), one of the most important oil crops worldwide, we report that flooding represses seed germination by mediating glycometabolism, anaerobic respiration and phytohormones biosynthesis related cascades. Phenotypic analysis showed that the flooding stress significantly decreases seed vigor and thus seed germination. Biochemical analysis demonstrated flooding leads to a decrease in several types of sugar contents during seed imbibition and an increase of cell conductivity as well as ethanol level, which remarkably inhibits seed germination. Subsequent transcriptomics and qPCR assays revealed that the expression levels of ABA (abscisic acid) and GA (gibberellin) biosynthesis/signaling and glycometabolism as well as anaerobic respiration related genes are consistent with the phenotypic and biochemical evidences. Furthermore, the exogenous sucrose or GA treatments can partially rescue the flooding or hypoxia-mediated repression of seed germination. Taken together, this study reveals that flooding stress impairs seed germination by decreasing sugar and phytohormones biosynthesis as well as promote anaerobic respiration. [ABSTRACT FROM AUTHOR]