Abscisic Acid Biosynthesis Inhibitor Research Articles

The AGAMOUS-LIKE 16-GENERAL REGULATORY FACTOR 1 module regulates axillary bud outgrowth via catabolism of abscisic acid in cucumber.

Lateral branches are important components of shoot architecture and directly affect crop yield and production cost. Although sporadic studies have implicated abscisic acid (ABA) biosynthesis in axillary bud outgrowth, the function of ABA catabolism and its upstream regulators in shoot branching remain elusive. Here, we showed that the MADS-box transcription factor AGAMOUS-LIKE 16 (CsAGL16) is a positive regulator of axillary bud outgrowth in cucumber (Cucumis sativus). Functional disruption of CsAGL16 led to reduced bud outgrowth, whereas overexpression of CsAGL16 resulted in enhanced branching. CsAGL16 directly binds to the promoter of the ABA 8'-hydroxylase gene CsCYP707A4 and promotes its expression. Loss of CsCYP707A4 function inhibited axillary bud outgrowth and increased ABA levels. Elevated expression of CsCYP707A4 or treatment with an ABA biosynthesis inhibitor largely rescued the Csagl16 mutant phenotype. Moreover, cucumber General Regulatory Factor 1 (CsGRF1) interacts with CsAGL16 and antagonizes CsAGL16-mediated CsCYP707A4 activation. Disruption of CsGRF1 resulted in elongated branches and decreased ABA levels in the axillary buds. The Csagl16 Csgrf1 double mutant exhibited a branching phenotype resembling that of the Csagl16 single mutant. Therefore, our data suggest that the CsAGL16-CsGRF1 module regulates axillary bud outgrowth via CsCYP707A4-mediated ABA catabolism in cucumber. Our findings provide a strategy to manipulate ABA levels in axillary buds during crop breeding to produce desirable branching phenotypes.

The 14-3-3 Protein BdGF14a Increases the Transcriptional Regulation Activity of BdbZIP62 to Confer Drought and Salt Resistance in Tobacco.

BdGF14a, a 14-3-3 gene from Brachypodium distachyon, induced by salt, H2O2, and abscisic acid (ABA), improved tolerance to drought and salt in tobacco, with a higher survival rate and longer roots under these stresses. Additionally, physiological index analyses showed that the heterologous expression of BdGF14a induced higher expression levels of antioxidant enzymes and their activities, leading to lighter DAB and NBT staining, denoting decreased H2O2 content. Additionally, the lower MDA content and ion leakage indicated enhanced cell membrane stability. Moreover, exogenous ABA resulted in shorter roots and a lower stomatal aperture in BdGF14a transgenic plants. BdGF14a interacted with NtABF2 and regulated the expression of stress-related genes. However, adding an ABA biosynthesis inhibitor suppressed most of these changes. Furthermore, similar salt and drought resistance phenotypes and physiological indicators were characterized in tobacco plants expressing BdbZIP62, an ABRE/ABF that interacts with BdGF14a. And Y1H and LUC assays showed that BdGF14a could enhance the transcription regulation activity of NtABF2 and BdbZIP62, targeting NtNECD1 by binding to the ABRE cis-element. Thus, BdGF14a confers resistance to drought and salinity through interaction with BdbZIP62 and enhances its transcriptional regulation activity via an ABA-mediated signaling pathway. Therefore, this work offers novel target genes for breeding salt- and drought-tolerant plants.

A 14-3-3 Protein-Encoding Gene, BdGF14g, Confers Better Drought Tolerance by Regulating ABA Biosynthesis and Signaling

Abscisic acid (ABA), a phytohormone, enacts a cardinal function in coping with abiotic stress. 14-3-3 proteins can interact with ABA-responsive-element-binding transcription factors (ABFs), a chief constituent of ABA signaling, and play critical roles in the dehydration response involving ABA signaling. Meanwhile, whether and how 14-3-3 proteins regulate ABA signaling to respond to aridity stress is yet to be fully investigated. Herein, BdGF14g, a 14-3-3 gene induced by ABA, H2O2, and PEG treatments, was identified in Brachypodium distachyon (B. distachyon). Overexpression of BdGF14g improved drought stress tolerance in tobacco plants, with a higher survival rate, longer root length, enhanced cell membrane stability, and increased antioxidase activity compared with non-transgenic controls in coping with dehydration. Both drought and exogenous ABA treatments resulted in smaller stomatal apertures in BdGF14g-transgenic lines. Additionally, when an ABA biosynthesis inhibitor was added, the better growth statuses, less H2O2 accumulation, and higher activities of catalase and superoxide dismutase under mannitol stress disappeared. Moreover, BdGF14g interacted with NtABF2, upregulated the endogenous ABA content, and enhanced the transcription of ABA-related genes, including NtNCED1, a crucial ABA biosynthesis gene, under drought conditions. In conclusion, BdGF14g acts as a positive factor in the water deficiency response by affecting ABA biosynthesis and signaling in tobacco plants.

Exogenously applied abscisic acid accelerates wound healing of Chinese yam tubers (Dioscorea opposita) through promoting suberin polyphenolics biosynthesis

Water loss, nutrient elution and pathogen attacks caused by mechanical wounding are the primary sources of postharvest loss of fruit and vegetables. Continuously increasing information has unraveled that abscisic acid (ABA) can accelerate wound healing of fruit and vegetables via stimulating suberin polyphenolics (SPP) biosynthesis, whereas the effect of ABA in wound healing of Chinese yam tubers remains unclear. The treatment of ABA and fluridone (FLD, an inhibitor of ABA biosynthesis) on postharvest wound healing of yam tubers was investigated in this study. The results showed that ABA treatment facilitated wound healing process of yam tubers, representing by the reduced weight loss and relative electrolyte leakage (REL). ABA enhanced the expression levels of phenylalanine ammonialyase (PAL), cinnamic acid 4-hydroxylase (C4H) and 4-coumarate-CoA ligase (4CL), as well as the corresponding enzyme contents and activities. Correspondingly, the contents of major monomers such as ferulic acid, caffeic acid and p-coumaric acid also increased. Simultaneously, ABA could improve the expression of peroxidase (POD), the enzyme content and activity, as well as hydrogen peroxide (H2O2) production, which might contribute to the polymerization of SPP and lignin. Inversely, inhibition of ABA production by FLD application displayed an opposite effect to ABA treatment. These results demonstrate that application of ABA stimulated wound healing of Chinese yam tubers via improving the gene expressions of relevant enzymes, their contents and activities, so that maintain high quality of postharvest yam tubers.

ABA is required for differential cell wall acidification associated with root hydrotropic bending in tomato.

Hydrotropism is an important adaptation of plant roots to the uneven distribution of water, with current research mainly focused on Arabidopsis thaliana. To examine hydrotropism in tomato (Solanum lycopersicum) primary roots, we used RNA sequencing to determine gene expression of root tips (apical 5 mm) on dry and wet sides of hydrostimulated roots grown on agar plates. Hydrostimulation enhances cell division and expansion on the dry side compared with the wet side of the root tip. In hydrostimulated roots, the abscisic acid (ABA) biosynthesis gene ABA4 was induced more on the dry than the wet side of root tips. The ABA biosynthesis inhibitor Fluridone and the ABA-deficient mutant notabilis (not) significantly decreased hydrotropic curvature. Wild-type, but not the ABA biosynthesis mutant not, root tips showed asymmetric H+ efflux, with greater efflux on the dry than on the wet side of root tips. Thus, ABA mediates asymmetric H+ efflux, allowing the root to bend towards the wet side to take up more water.

Role of the transcription factor MdABF2 in abscisic acid-induced volatile compound biosynthesis in ‘Ruixue’ (Malus × domestica) apple during storage

Fruit aroma, which is conferred by an array of volatile compounds, strongly influences both consumer acceptance and market competitiveness. The phytohormone abscisic acid (ABA) regulates volatile compound biosynthesis during fruit ripening. However, the regulatory mechanism by which ABA may alter the production of volatile compounds in apple remains unknown. In this study, ABA treatment accelerated fruit ripening and volatile compound production, whereas treatment with the ABA biosynthesis inhibitor nordihydroguaiaretic acid (NDGA) resulted in the opposite effects. We identified a nuclear-localized ABA-responsive transcription factor (TF), MdABF2, which was upregulated by exogenous ABA. Overexpression of MdABF2 resulted in enhanced production of volatile compounds and biosynthesis gene expression, and these effects were further enhanced by ABA treatment. Moreover, MdABF2 was found to bind directly to the MdLOX1a, MdLOX5a, MdAAT1, and MdAAT2 promoters, activating their expression. The results presented here contribute to our understanding of the mechanism by which ABA regulates volatile compound biosynthesis. Furthermore, these data will be beneficial for the molecular breeding and improvement of apple for better flavor and aroma.

Abscisic Acid Mediates Salicylic Acid Induced Chilling Tolerance of Grafted Cucumber by Activating H2O2 Biosynthesis and Accumulation.

Grafting is widely applied to enhance the tolerance of some vegetables to biotic and abiotic stress. Salicylic acid (SA) is known to be involved in grafting-induced chilling tolerance in cucumber. Here, we revealed that grafting with pumpkin (Cucurbita moschata, Cm) as a rootstock improved chilling tolerance and increased the accumulation of SA, abscisic acid (ABA) and hydrogen peroxide (H2O2) in grafted cucumber (Cucumis sativus/Cucurbita moschata, Cs/Cm) leaves. Exogenous SA improved the chilling tolerance and increased the accumulation of ABA and H2O2 and the mRNA abundances of CBF1, COR47, NCED, and RBOH1. However, 2-aminoindan-2-phosphonic acid (AIP) and L-a-aminooxy-b-phenylpropionic acid (AOPP) (biosynthesis inhibitors of SA) reduced grafting-induced chilling tolerance, as well as the synthesis of ABA and H2O2, in cucumber leaves. ABA significantly increased endogenous H2O2 production and the resistance to chilling stress, as proven by the lower electrolyte leakage (EL) and chilling injury index (CI). However, application of the ABA biosynthesis inhibitors sodium tungstate (Na2WO4) and fluridone (Flu) abolished grafting or SA-induced H2O2 accumulation and chilling tolerance. SA-induced plant response to chilling stress was also eliminated by N,N'-dimethylthiourea (DMTU, an H2O2 scavenger). In addition, ABA-induced chilling tolerance was attenuated by DMTU and diphenyleneiodonium (DPI, an H2O2 inhibitor) chloride, but AIP and AOPP had little effect on the ABA-induced mitigation of chilling stress. Na2WO4 and Flu diminished grafting- or SA-induced H2O2 biosynthesis, but DMTU and DPI did not affect ABA production induced by SA under chilling stress. These results suggest that SA participated in grafting-induced chilling tolerance by stimulating the biosynthesis of ABA and H2O2. H2O2, as a downstream signaler of ABA, mediates SA-induced chilling tolerance in grafted cucumber plants.

Abscisic Acid May Play a Critical Role in the Moderating Effect of Epichloë Endophyte on Achnatherum inebrians under Drought Stress.

Water scarcity is a major constraint that adversely affects plant development and growth. Abscisic acid (ABA) is a plant stress hormone that is rapidly synthesized and can induce stomatal closure to conserve water, thereby alleviating the drought stress of plants. The Epichloë endophyte enhances the drought tolerance of Achnatherum inebrians (drunken horse grass, DHG). To better understand how the Epichloë endophyte enhances drought tolerance, DHG plants without (EF) and with (EI), an Epichloë endophyte, were grown under 20% and 60% soil water conditions (SWC), and the leaves of the three treatments of EF and EI plants were sprayed with ABA solution (1 mg/L); fluridone (FLU), the ABA biosynthesis inhibitor solution (1 mg/L); and distilled water, respectively. Four-weeks later, the results indicated that the exogenous ABA application promoted plant growth, stomatal conductance, and photosynthetic rate, while the opposite effect occurred with plants sprayed with FLU. The differences between EI and EF plants in tiller number, height, chlorophyll content, stomata conductance, and photosynthetic rate were highest when sprayed with ABA. Thus, it is concluded that ABA might be involved in the moderating effect of Epichloë endophytes on DHG plants exposed to drought by maintaining growth and improving photosynthetic efficiency.

Rutin Stimulates the Green Alga Chromochloris zofingiensis for Improved Biomass and Astaxanthin Production.

Chromochloris zofingiensis represents a potential algal producer of the value-added ketocarotenoid astaxanthin. Here, rutin, a low-cost flavonoid compound, was evaluated regarding its roles in C. zofingiensis production under astaxanthin-inducing conditions via physiological, biochemical, and transcriptomics analyses. The rutin treatment allowed C. zofingiensis to achieve 81.2% more biomass and 20.5% greater astaxanthin content under nitrogen deprivation, leading to more than doubled astaxanthin production. The rutin-treated C. zofingiensis had higher levels of chlorophylls, proteins, and lipids and lower carbohydrate level than the control. Rutin promoted the intracellular abscisic acid (ABA) level, which could be restored by the ABA biosynthesis inhibitor, accompanied by the restoration of biomass concentration and astaxanthin content. The application of exogenous ABA to C. zofingiensis also furthered biomass concentration and astaxanthin accumulation. Together with the comparative transcriptomics analysis, our study provides implications into the involvement of ABA in rutin-mediated stimulation of C. zofingiensis growth and astaxanthin accumulation and highlights a feasible strategy of combining stress and chemical induction for improved microalgal production.

WRKY41/WRKY46-miR396b-5p-TPR module mediates abscisic acid-induced cold tolerance of grafted cucumber seedlings.

Grafting is one of the key agronomic measures to enhance the tolerance to environmental stresses in horticultural plants, but the specific molecular regulation mechanism in this tolerance largely remains unclear. Here, we found that cucumber grafted onto figleaf gourd rootstock increased cold tolerance through abscisic acid (ABA) activating WRKY41/WRKY46-miR396b-5p-TPR (tetratricopeptide repeat-like superfamily protein) module. Cucumber seedlings grafted onto figleaf gourd increased cold tolerance and induced the expression of miR396b-5p. Furthermore, overexpression of cucumber miR396b-5p in Arabidopsis improved cold tolerance. 5’ RNA ligase-mediated rapid amplification of cDNA ends (5’ RLM-RACE) and transient transformation experiments demonstrated that TPR was the target gene of miR396b-5p, while TPR overexpression plants were hypersensitive to cold stress. The yeast one-hybrid and dual-luciferase assays showed that both WRKY41 and WRKY46 bound to MIR396b-5p promoter to induce its expression. Furthermore, cold stress enhanced the content of ABA in the roots and leaves of figleaf gourd grafted cucumber seedlings. Exogenous application of ABA induced the expression of WRKY41 and WRKY46, and cold tolerance of grafted cucumber seedlings. However, figleaf gourd rootstock-induced cold tolerance was compromised when plants were pretreated with ABA biosynthesis inhibitor. Thus, ABA mediated figleaf gourd grafting-induced cold tolerance of cucumber seedlings through activating the WRKY41/WRKY46-miR396b-5p-TPR module.

ABA signaling mediates 5-aminolevulinic acid-induced anthocyanin biosynthesis in red pear fruits

Peel color is an important quality trait of pears and directly affects its commercial value. Although several studies have reported that exogenous 5-aminolevulinic acid (ALA) induces anthocyanin biosynthesis, the mechanisms involved remain unclear. The purpose of this study was to confirm the effects of ALA on anthocyanin biosynthesis in the red pear ‘Nanhong’ and elucidate the effect of abscisic acid (ABA) on ALA-induced anthocyanin accumulation. Application of ALA solution (100 or 300 mg L−1) promoted arbutin, flavonol, and anthocyanin accumulation, but decreased chlorogenic acid and flavanol content, especially at 300 mg L−1. The structural gene transcriptional levels and transcription factors (PuMYB10 and PubHLH33) associated with anthocyanin synthesis were also enhanced by ALA treatment. Furthermore, ALA treatment increased the endogenous ABA content and upregulated the expression of ABA biosynthesis-related genes. Additionally, the influence of ALA on anthocyanin biosynthesis was removed by the ABA biosynthesis inhibitor fluridone, while the expression of PuMYB10, PuUFGT, and PuGSTF12, which were induced by exogenous ABA and ALA treatments, was suppressed. These results suggest that ABA signaling plays a crucial role in ALA-induced anthocyanin accumulation in red pear fruits. The results can provide a theoretical basis for improving the color and fruit quality of red pears.

Priming effect of exogenous ABA on heat stress tolerance in rice seedlings is associated with the upregulation of antioxidative defense capability and heat shock-related genes

Heat stress is a major restrictive factor that suppresses rice production. In this study, we investigated the potential priming effect of exogenous abscisic acid (ABA) on heat tolerance in rice seedlings. Seedlings were pretreated with 10 µM ABA by root-drenched for 24 h and then subjected to heat stress conditions of 40 °C day/35 °C night. ABA pretreatment significantly decreased leaf withering by 2.5–28.5% and chlorophyll loss by 12.8–35.1% induced by heat stress in rice seedlings. ABA pretreatment also mitigated cell injury, as shown by lower malondialdehyde content, relative electrolytic conductivity, and expression of cell death-related genes OsKOD1, OsCP1, and OsNAC4, while expression of OsBI1, a cell death-suppressor gene, was upregulated by ABA pretreatment. Moreover, ABA pretreatment improved antioxidant defense capacity, as shown by an obvious upregulation of ROS-scavenging genes and a decrease in ROS content (O2− and H2O2), and downregulation of the OsRbohs genes. Application of fluridone, an ABA biosynthesis inhibitor, increased membrane injury and the accumulation of ROS under heat stress. Exogenous antioxidants (proanthocyanidins) significantly alleviated leaf withering by decreasing ROS overaccumulation and membrane injury induced by heat stress. In addition, ABA pretreatment significantly superinduced the expression of ABA-responsive genes SalT and OsWsi18, the ABA biosynthesis genes OsNCED3 and OsNCED4, and the heat shock-related genes OsHSP23.7, OsHSP17.7, OsHSF7, and OsHsfA2a. Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing heat stress tolerance of rice seedlings mainly by improving antioxidant defense capacity and heat shock-related genes.

Novel small molecules targeting bZIP23 TF improve stomatal conductance and photosynthesis under mild drought stress by regulating ABA.

Drought-induced abscisic acid (ABA) accumulation plays a key role in plant water relations by regulating stomatal movements. Although ABA helps in the survival of the plants, reduced carbon gain affects plant productivity. To improve crop productivity under mild drought stress conditions, it is necessary to manipulate ABA responses. Other research groups have used forward chemical genomics for the identification of ABA agonists and antagonists aiming to manipulate ABA biosynthesis and signalling. In the present study, we identified indolyl-ethyl amine and serotonin small molecules using a reverse chemical genomics approach, with these acting as potent inhibitors of ABA biosynthesis through transient regulation of bZIP23 transcription factor activity. In rice, wheat and soybean, each of the small molecules enhanced the germination of seeds, even in the presence of ABA. These molecules nullified the effect of ABA on intact and detached leaves, resulting in higher photosynthesis. Furthermore, these small molecules effectively reduced the transcription levels of bZIP23 targeting NCED4, PP2C49 and CO3 genes. Rice plants treated with the small molecules were found to have improved stomatal conductance, spikelet fertility and yield compared to untreated plants under mild drought stress conditions. Our results suggest that indolyl-ethyl amine and serotonin small molecules could be utilized to improve yield under mild drought conditions.

ABA-responsive transcription factor ABF1-1 promotes JA biosynthesis to accelerate suberin polyphenolic formation in wounded kiwifruit (Actinidia chinensis)

Mechanical damage is a central limiting factor in the maintenance of the postharvest fruit quality during harvest, transportation, and processing. In this study, wounded kiwifruit (Actinidia chinensis cv. Xuxiang) were respectively treated with abscisic acid (ABA), fluridone (FLD, an inhibitor of ABA biosynthesis), methyl jasmonate (MeJA), diethyldithiocarbamic acid (DIECA, an inhibitor of JA biosynthesis), and ABA+DIECA to investigate the potential interaction between ABA and JA in the process of wound healing. The results showed that blocking JA biosynthesis significantly reduced the positive effect of ABA on the accumulation of suberin polyphenolic (SPP). Besides, transiently overexpressed the AchLOX3 and AchOPR3 in tobacco (Nicotiana benthamiana) leaves confirmed that these two genes respectively encoded lipoxygenase and 12-oxo-phytodienoic acid reductase involved in JA biosynthesis. Notably, the positive regulation of transcription factor (TF) AchABF1-1 on AchLOX3 and AchOPR3 was identified. ABA-induced AchABF-1 located in the nucleus and activated the transcriptional expression of AchLOX3 and AchOPR3 through binding to their promoters. These results were further confirmed in the tobacco leaves overexpressing AchABF1-1 in which AchABF1-1 promoted NbLOX and NbOPR expression with the increases of JA content. In addition, exogenous ABA increased endogenous JA content, and enhanced LOX and OPR activities as well as their related gene expression, while FLD reduced these indices. These results suggested that the promotion effect of JA on the SPP accumulation was enhanced through the promotion of JA biosynthesis by ABA-responsive transcription factor AchABF1-1 during the wound healing process of kiwifruit.

Plant hormone signals regulate trehalose accumulation against osmotic stress in watermelon cells.

Trehalose, one of the most chemically stable sugars, can effectively improve the tolerance of various plants against abiotic stress by protecting and stabilizing protein and cell membranes. However, the signaling pathway in trehalose biosynthesis triggered by abiotic stresses is still unclear. In the study, it can be shown that exogenous trehalose can alleviate the inhibitory effect of osmotic stress on cell growth, suppress extracellular alkalization, ROS burst, and maintain the integrity of the microtubular cytoskeleton. Trehalose-6-phosphate synthase (TPS) is the key limiting enzyme for trehalose synthesis and is encoded by 7 ClTPS genes, located in 7 different chromosomes of the watermelon genome. Expression analysis by qRT-PCR indicated that osmotic stress could upregulate the expression of all the family members of ClTPS and promote the accumulation of trehalose in watermelon cells accordingly. Exogenous methyl jasmonate (MeJA), ethephon (ETH), abscisic acid (ABA), or salicylic acid (SA) induced trehalose accumulation, with MeJA being the most effective treatment. When fluridone (FL), an ABA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, trehalose accumulation and packed cell volume were suppressed significantly, whereas inhibition of ethylene biosynthesis could even restore cell growth. Moreover, inhibition of trehalose hydrolysis could also increase the tolerance against osmotic stress. This study shows that trehalose biosynthesis is phytohormone-dependent and the hydrolysis of trehalose is involved in osmotic tolerance regulation.

Abscisic acid is required for exodermal suberization to form a barrier to radial oxygen loss in the adventitious roots of rice (Oryza sativa).

To acclimate to waterlogged conditions, wetland plants form a barrier to radial oxygen loss (ROL) that can enhance oxygen transport to the root apex. We hypothesized that one or more hormones are involved in the induction of the barrier and searched for such hormones in rice. We previously identified 98 genes that were tissue-specifically upregulated during ROL barrier formation in rice. The RiceXPro database showed that most of these genes were highly enhanced by exogenous abscisic acid (ABA). We then examined the effect of ABA on ROL barrier formation by using an ABA biosynthesis inhibitor (fluridone, FLU), by applying exogenous ABA and by examining a mutant with a defective ABA biosynthesis gene (osaba1). FLU suppressed barrier formation in a stagnant solution that mimics waterlogged soil. Under aerobic conditions, rice does not naturally form a barrier, but 24 h of ABA treatment induced barrier formation. osaba1 did not form a barrier under stagnant conditions, but the application of ABA rescued the barrier. In parallel with ROL barrier formation, suberin lamellae formed in the exodermis. These findings strongly suggest that ABA is an inducer of suberin lamellae formation in the exodermis, resulting in an ROL barrier formation in rice.

Melatonin Pretreatment Confers Heat Tolerance and Repression of Heat-Induced Senescence in Tomato Through the Modulation of ABA- and GA-Mediated Pathways.

Heat stress and abscisic acid (ABA) induce leaf senescence, whereas melatonin (MT) and gibberellins (GA) play critical roles in inhibiting leaf senescence. Recent research findings confirm that plant tolerance to diverse stresses is closely associated with foliage lifespan. However, the molecular mechanism underlying the signaling interaction of MT with GA and ABA regarding heat-induced leaf senescence largely remains undetermined. Herein, we investigated putative functions of melatonin in suppressing heat-induced leaf senescence in tomato and how ABA and GA coordinate with each other in the presence of MT. Tomato seedlings were pretreated with 100 μM MT or water and exposed to high temperature (38/28°C) for 5 days (d). Heat stress significantly accelerated senescence, damage to the photosystem and upregulation of reactive oxygen species (ROS), generating RBOH gene expression. Melatonin treatment markedly attenuated heat-induced leaf senescence, as reflected by reduced leaf yellowing, an increased Fv/Fm ratio, and reduced ROS production. The Rbohs gene, chlorophyll catabolic genes, and senescence-associated gene expression levels were significantly suppressed by MT addition. Exogenous application of MT elevated the endogenous MT and GA contents but reduced the ABA content in high-temperature-exposed plants. However, the GA and ABA contents were inhibited by paclobutrazol (PCB, a GA biosynthesis inhibitor) and sodium tungstate (ST, an ABA biosynthesis inhibitor) treatment. MT-induced heat tolerance was compromised in both inhibitor-treated plants. The transcript abundance of ABA biosynthesis and signaling genes was repressed; however, the biosynthesis genes MT and GA were upregulated in MT-treated plants. Moreover, GA signaling suppressor and catabolic gene expression was inhibited, while ABA catabolic gene expression was upregulated by MT application. Taken together, MT-mediated suppression of heat-induced leaf senescence has collaborated with the activation of MT and GA biosynthesis and inhibition of ABA biosynthesis pathways in tomato.

Changes in the cell wall components produced by exogenous abscisic acid treatment in strawberry fruit

Fruit development and ripening are controlled by multiple plant hormones; for strawberries, recent evidence supports the role of abscisic acid (ABA) as a promoter of fruit ripening. Fruit softening during ripening is mainly a consequence of the solubilization and depolymerization of cell wall components mediated by the action of a complex set of enzymes and proteins. In the present work, we performed a comparative study (ABA-treatment vs. control) of the changes in the physiological properties of the cell wall-associated polysaccharide contents of strawberry fruit (Fragaria x ananassa ‘Camarosa’) via analysis of thermogravimetry (TG) combined with analysis of mRNA abundance, enzymatic activity and physiological characteristics. ‘Camarosa’ did not show a decline in the fruit firmness at 48 h post-treatment; however, we observed changes in cell wall stability based on the TG and differential thermogravimetric (DTG) analysis curves, which demonstrated the degradation of the cell wall polymers after ABA hormone treatment for 48 h, principally for hemicellulose polymers. Additionally, DTG analysis showed that dried samples derived from the treatment of the fruit with the ABA biosynthesis inhibitor fluridone maintained the same thermal stability as the control samples. Finally, the existence of a relationship between thermal stability, transcriptional analysis and enzymatic activity after hormone treatment was demonstrated, which provides the basis for a model for understanding the changes in the cell wall polymers of F. x ananassa mediated by the ABA hormone during fruit ripening.

ABA stimulates wound suberization through antagonizing the MYB4-mediated transcriptional repression of CYP86A1 and FAR in postharvest kiwifruit

Abstract Suberin biosynthesis involves a large number of genes, and many of them are induced by abscisic acid (ABA). However, the regulation of transcription factor (TF) in response to ABA on suberin biosynthetic genes in kiwifruit has been unexplored. In this study, two genes, AchnCYP86A1 and AchnFAR respectively encoding a fatty acid ω-hydroxylase and fatty acyl-CoA reductase involved in suberin monomer biosynthesis were demonstrated in transient overexpressed tobacco (Nicotiana benthamiana). Notably, the negative regulation of AchnMYB4 on AchnCYP86A1 and AchnFAR was identified. AchnMYB4 could repress AchnCYP86A1 and AchnFAR transcript by directly binding to the gene promoter in yeast one-hybrid and dual-luciferase assays. These results were further confirmed in transient overexpressed tobacco leaves in that AchnMYB4 significantly down-regulated suberin biosynthetic genes including CYP86A1, FAR2 and FAR3, and reduced accumulation of ω-hydroxyacids and primary alcohols. Moreover, exogenous ABA could induce the expression of AchnCYP86A1 and AchnFAR, and the accumulation of corresponding suberin monomers by inhibition of AchnMYB4 in wound-tissue of kiwifruit. However, fluridone (an inhibitor of ABA biosynthesis) was found to counter the inductive effects of ABA. Taken together, the results suggest that ABA activates AchnCYP86A1 and AchnFAR to promote suberin monomers biosynthesis by inhibiting AchnMYB4.

Quantitative proteomics reveals dual effects of calcium on radicle protrusion in soybean

To reveal calcium-mediated germination in soybean, a gel-free/label-free proteomics was performed in radicle of seed imbibed with CaCl2. Morphological analysis presented promoting and suppressing performance of seed growth under 5 and 50 mM CaCl2, respectively. A total of 106 and 581 proteins were identified in response to 5 and 50 mM CaCl2, respectively. Among 33 proteins, which were simultaneously affected by 5 and 50 mM CaCl2 imbibition, proteins related to protein metabolism, cell, development, and stress showed reversed abundance in response to CaCl2 on dose-dependent manner. Notably, protein abundance of late embryogenesis abundant (LEA) 4–5, LEA4, and dehydrin decreased and increased by 5 and 50 mM CaCl2, respectively, consistent with the transcript level. Moreover, inhibited biosynthesis of gibberellic acid repressed growth of 5 mM CaCl2-imbibed soybean, while inhibition of abscisic acid biosynthesis released the suppressing effects of 50 mM CaCl2. Taken together, these results suggest that decreased or increased protein abundance of LEA4–5, LEA4, and dehydrin might determine promoting or suppressing effects of low or high level of calcium on soybean through enhancing seed sensitivity to gibberellic acid or abscisic acid during radicle protrusion. SignificanceCalcium serves as a versatile signal in plant growth; however, calcium-mediated germination on dose-dependent manner remains elusive. In this study, dual effects of calcium on radicle protrusion in soybean were investigated using proteomic approach. Radicle growth of germinating seed was improved by 5 mM CaCl2; however, it was retarded by 50 mM CaCl2. Late embryogenesis abundant (LEA) 4–5, LEA4, and dehydrin displayed converse profiles in response to low and high concentrations of CaCl2 at both protein abundance and gene expression level. Inhibited biosynthesis of gibberellic acid (GA) significantly impeded radicle protrusion in presence of low concentration of CaCl2, while inhibiting of abscisic acid (ABA) biosynthesis released suppression induced by high concentration of CaCl2. These findings suggest that LEA proteins are associated with calcium-mediated radicle protrusion on dose-dependent manner, and seed sensitivity to GA and ABA might determine promoting and suppressing effects of calcium on radicle protrusion in soybean.