Nine-cis-epoxycarotenoid Dioxygenase Research Articles

Root-derived long-distance signals trigger ABA synthesis and enhance drought resistance in Arabidopsis

Vascular plants have evolved intricate long-distance signaling mechanisms to cope with environmental stress, with reactive oxygen species (ROS) emerging as pivotal systemic signals in plant stress responses. However, the exact role of ROS as root-to-shoot signals in the drought response has not been determined. In this study, we reveal that compared with wild-type plants, ferric reductase defective 3 (frd3) mutants exhibit enhanced drought resistance concomitant with elevated NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) transcript levels and abscisic acid (ABA) contents in leaves as well as increased hydrogen peroxide (H2O2) levels in roots and leaves. Grafting experiments distinctly illustrate that drought resistance can be conferred by the frd3 rootstock regardless of the scion genotype, indicating that long-distance signals originating from frd3 roots promote an increase in ABA levels in leaves. Intriguingly, the drought resistance conferred by the frd3 mutant rootstock is weakened by the CAT2-overexpressing scion, suggesting that H2O2 may be involved in long-distance signaling. Moreover, the results of comparative transcriptome and proteome analyses support the drought resistance phenotype of the frd3 mutant. Taken together, our findings substantiate the notion that frd3 root-derived long-distance signals trigger ABA synthesis in leaves and enhance drought resistance, providing new evidence for root-to-shoot long-distance signaling in the drought response of plants.

Temporal transcriptome and metabolite analyses provide insights into the biochemical and physiological processes underlying endodormancy release in pistachio (Pistacia vera L.) flower buds.

Pistachio (Pistacia vera L.), an economically and nutritionally important tree crop, relies on winter chill for bud endodormancy break and subsequent blooming and nut production. However, insufficient winter chill poses an increasing challenge in pistachio growing regions. To gain a better understanding of the physiological and biochemical responses of endodormant pistachio buds to chilling accumulation, we investigated the global gene expression changes in flower buds of pistachio cv. Kerman that were cultivated at three different orchard locations and exposed to increasing durations of winter chill. The expression of genes encoding β-1,3-glucanase and β-amylase, enzymes responsible for breaking down callose (β-1,3-glucan) and starch (α-1,4-glucan), respectively, increased during the endodormancy break of pistachio buds. This result suggested that the breakdown of callose obstructing stomata as well as the release of glucose from starch enables symplasmic trafficking and provides energy for bud endodormancy break and growth. Interestingly, as chilling accumulation increased, there was a decrease in the expression of nine-cis-epoxycarotenoid dioxygenase (NCED), encoding an enzyme that uses carotenoids as substrates and catalyzes the rate-limiting step in abscisic acid (ABA) biosynthesis. The decrease in NCED expression suggests ABA biosynthesis is suppressed, thus reducing inhibition of endodormancy break. The higher levels of carotenoid precursors and a decrease in ABA content in buds undergoing endodormancy break supports this suggestion. Collectively, the temporal transcriptome and biochemical analyses revealed that the degradation of structural (callose) and non-structural (starch) carbohydrates, along with the attenuation of ABA biosynthesis, are critical processes driving endodormancy break in pistachio buds.

Characterization of Carotenoid Cleavage Oxygenase Genes in Cerasus humilis and Functional Analysis of ChCCD1.

Carotenoid cleavage oxygenases (CCOs) are key enzymes that function in degrading carotenoids into a variety of apocarotenoids and some other compounds. In this study, we performed genome-wide identification and characterization analysis of CCO genes in Cerasus humilis. Totally, nine CCO genes could be classified into six subfamilies, including carotenoid cleavage dioxygenase 1 (CCD1), CCD4, CCD7, CCD8, CCD-like and nine-cis-epoxycarotenoid dioxygenase (NCED), were identified. Results of gene expression analysis showed that ChCCOs exhibited diverse expression patterns in different organs and in fruits at different ripening stages. To investigate the roles of ChCCOs in carotenoids degradation, enzyme assays of the ChCCD1 and ChCCD4 were performed in Escerichia coli BL21(DE3) that can accumulate lycopene, β-carotene and zeaxanthin. The prokaryotic expressed ChCCD1 resulted in obvious degradation of lycopene, β-carotene and zeaxanthin, but ChCCD4 did not show similar functions. To further determine the cleaved volatile apocarotenoids of these two proteins, headspace gas chromatography/mass spectrometer analysis was performed. Results showed that ChCCD1 could cleave lycopene at 5, 6 and 5', 6' positions to produce 6-methy-5-hepten-2-one and could catalyze β-carotene at 9, 10 and 9', 10' positions to generate β-ionone. Our study will be helpful for clarifying the roles of CCO genes especially ChCCD1 in regulating carotenoid degradation and apocarotenoid production in C. humilis.

OsWR2 recruits HDA704 to regulate the deacetylation of H4K8ac in the promoter of OsABI5 in response to drought stress.

Drought stress is a major environmental factor that limits the growth, development, and yield of rice (Oryza sativa L.). Histone deacetylases (HDACs) are involved in the regulation of drought stress responses. HDA704 is an RPD3/HDA1 class HDAC that mediates the deacetylation of H4K8 (lysine 8 of histone H4) for drought tolerance in rice. In this study, we show that plants overexpressing HDA704 (HDA704-OE) are resistant to drought stress and sensitive to abscisic acid (ABA), whereas HDA704 knockout mutant (hda704) plants displayed decreased drought tolerance and ABA sensitivity. Transcriptome analysis revealed that HDA704 regulates the expression of ABA-related genes in response to drought stress. Moreover, HDA704 was recruited by a drought-resistant transcription factor, WAX SYNTHESIS REGULATORY 2 (OsWR2), and co-regulated the expression of the ABA biosynthesis genes NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3), NCED4, and NCED5 under drought stress. HDA704 also repressed the expression of ABA-INSENSITIVE 5 (OsABI5) and DWARF AND SMALL SEED 1 (OsDSS1) by regulating H4K8ac levels in the promoter regions in response to polyethylene glycol 6000 treatment. In agreement, the loss of OsABI5 function increased resistance to dehydration stress in rice. Our results demonstrate that HDA704 is a positive regulator of the drought stress response and offers avenues for improving drought resistance in rice.

Temperature modulation of CAMTA3 gene induction activity is mediated through the DNA binding domain.

The calmodulin-binding transcription activator (CAMTA) proteins of Arabidopsis thaliana play a major role in cold acclimation, contributing to the rapid induction of the C-REPEAT BINDING FACTOR (CBF) genes and other genes that impart freezing tolerance in plants exposed to cold temperature (4°C). The goal of this study was to better understand how the gene induction activity of CAMTA3 is modulated by temperature. Our results indicate that a severely truncated version of CAMTA3, CAMTA3334 , which includes the N-terminal CG-1 DNA binding domain and a newly identified transcriptional activation domain (TAD), was able to rapidly induce the expression of CBF2 and two newly identified target genes, EXPANSIN-LIKE A1 (EXPL1) and NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3), in response to cold temperature. Additionally, CAMTA3334 was able to restore freezing tolerance when expressed in a camta23 double mutant. The ability of CAMTA3 and CAMTA3334 to induce target genes at cold temperature did not involve increased levels of these proteins or increased binding of these proteins to target gene promoters in cold-treated plants. Rather, domain-swapping experiments indicated that the CAMTA3 CG-1 domain conferred temperature dependence to the ability of the CAMTA3 TAD to induce gene expression. The CG-1 domain also enabled the TAD to induce the expression of target genes at a moderate temperature (22°C) in response to cycloheximide treatment, consistent with the TAD activity not being intrinsically temperature dependent. We propose a working model in which the temperature modulation of CAMTA3 gene induction activity occurs independently from the C-terminal calmodulin-binding domains that previously have been proposed to activate CAMTA3 transcriptional activity in response to cold temperature.

Identification of the carotenoid cleavage dioxygenase genes and functional analysis reveal DoCCD1 is potentially involved in beta-ionone formation in Dendrobium officinale.

The carotenoids are the most widely distributed secondary metabolites in plants and can be degraded by carotenoid cleavage dioxygenase (CCD) to form apocarotenoids including an important C13 compound beta-ionone. Volatile beta-ionone can confer the violet and woody fragrance to plant essential oils, flowers, fruits, and vegetables, which therefore has been used in various industries. Dendrobium officinale is a traditional medicinal plant. However, there was limited information on the key enzymes involved in the biosynthesis of beta-ionone in D. officinale. In the present study, beta-ionone was detected in stems and leaves of D. officinale and genome-wide identification and expression profiles of CCD genes were subsequently carried out. There were nine DoCCD members in D. officinale. According to the phylogenetic relationship, DoCCD proteins were classified into six subfamilies including CCD1, CCD4, CCD7, CCD8, nine-cis-epoxycarotenoid dioxygenase (NCED) and zaxinone synthase (ZAS). DoCCD genes showed distinctive expression profiles and DoCCD1 gene was abundantly expressed in eight tissues. Induced expression of DoCCD1 gene resulted in discoloration of Escerichia coli strains that can accumulate carotenoids. Analysis of Gas Chromatography/Mass Spectrometer showed that DoCCD1 enzyme can cleave lycopene to produce 6-methyl-5-hepten-2-one and pseudoionone and also catalyze beta-carotene to form beta-ionone. Expression of DoCCD1 gene in Nicotiana benthamiana leaf resulted in production of abundant beta-ionone. Overall, the present study first provides valuable information on the CCD gene family in D. officinale, function of DoCCD1 gene as well as production of beta-ionone through genetic modification.

Genome-wide identification, characterization and expression profiles of the CCD gene family in Gossypium species.

The online version contains supplementary material available at 10.1007/s13205-021-02805-9.

Expression of a NGATHA1 Gene from Medicago truncatula Delays Flowering Time and Enhances Stress Tolerance.

Shoot branching is one of the most variable determinants of crop yield, and the signaling pathways of plant branches have become a hot research topic. As an important transcription factor in the B3 family, NGATHA1 (NGA1), plays an important role in regulating plant lateral organ development and hormone synthesis and transport, but few studies of the role of this gene in the regulation of plant growth and stress tolerance have been reported. In this study, the NGA1 gene was isolated from Medicago truncatula (Mt) and its function was characterized. The cis-acting elements upstream of the 5′ end of MtNGA1 and the expression pattern of MtNGA1 were analyzed, and the results indicated that the gene may act as a regulator of stress resistance. A plant expression vector was constructed and transgenic Arabidopsis plants were obtained. Transgenic Arabidopsis showed delayed flowering time and reduced branching phenotypes. Genes involved in the regulation of branching and flowering were differentially expressed in transgenic plants compared with wild-type plants. Furthermore, transgenic plants demonstrated strong tolerances to salt- and mannitol-induced stresses, which may be due to the upregulated expression of NCED3 (NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3) by the MtNGA1 gene. These results provide useful information for the exploration and genetic modification use of MtNGA1 in the future.

Exploring the codon patterns between CCD and NCED genes among different plant species

Plant carotenoid cleavage oxygenase (CCO) is an enzyme which catalyzes carotenoids to apocarotenoid products that are involved in several vital physiological functions. The CCO exists in two forms, namely, CCD (Carotenoid Cleavage Dioxygenase) and NCED (Nine-Cis Epoxycarotenoid Dioxygenase). This paper relates to a comparative study on CCD and NCED genes through phylogeny and codon usage analysis. The result of the phylogenetic analysis indicates a closer relationship between CCD and NCED subclass genes, while the RSCU values indicate a high preference for CUC codon in both CCD and NCED gene families. The mean ENc value of NCED genes was found to be 48.76, suggesting a higher codon bias compared to CCD genes. However, the ENc-GC3S plot suggests that both the gene families are under mutational pressure with variations according to their species-specific role. Similarly, the multivariate analysis also suggests that nucleotide mutation bias influences codon usage. Correlation analysis of Axis I and codon adaptation index values indicate a significant correlation between critical indices. Even though the prominence of the variations in codon usage between the two gene families, they are exerted towards the time-specific functional requirement for that plant species. This is evident from the cleaving roles of these enzymes against various carotenoids at different growth stages. The result of this investigation indicates that CCD and NCED genes are under mutational pressure. This codon bias study paves the way for increasing the production of apocarotenoids, which have a great significance in the industry.

Abscisic acid induced cellular responses of sub1A QTL to aluminium toxicity in rice (Oryza sativa L.)

Involvement of abscisic acid (ABA) was studied for aluminium (Al) sensitivity through functioning of sub1A quantitative trait loci in rice cultivars. sub1A quantitative trait loci bearing cv. Swarna Sub1 was found almost compatible with non sub1A quantitative trait loci bearing cv. Swarna for abscisic acid accumulation all through the aluminium concentrations. However, abscisic acid was self inductive by over expression of its biosynthetic gene in nine-cis-epoxycarotenoid dioxygenase 3 (NCED3) more in cv. Swarna than other. The effect of abscisic acid pretreatment was variable for specific leaf weight, leaf mass ratio and others for the cultivars. Bio-accumulation of aluminium had revealed the sensitivity of toxicity more in cv. Swarna than other. In connection to oxidative stress generation of reactive oxygen species was detected by both histochemical and in vitro assays through hematoxylin, Evans blue and schiff's reactions. Abscisic acid pretreatment had significantly reversed the effects of aluminium toxicity for reactive oxygen species generation. Regardless of varieties sensitivity of aluminium was more prone in shoot than root as detected by nitro blue tetrazolium and 3,3′-diaminobenzidine mediated signalling. Activity in metal chelation in extra cellular spaces monitored through esterase activity and that also established independence of abscisic acid pretreatment for cv. Swarna Sub1. The specific polymorphism of esterase at protein level strengthened the bio-monitoring of aluminium through the rice varieties as well its modulation with abscisic acid. Abscisic acid has been discussed an important effectors to modulate the tolerance pathway of rice cultivars through intrusion of sub1A quantitative trait loci.

Overexpression of the Soybean NAC Gene GmNAC109 Increases Lateral Root Formation and Abiotic Stress Tolerance in Transgenic Arabidopsis Plants

NACs are plant-specific transcription factors that have crucial roles in plant development and biotic and/or abiotic stress responses. This study characterized the functions of the soybean NAC gene GmNAC109 using an overexpression construct in Arabidopsis lines. Sequence analysis revealed that GmNAC109 is highly homologous to ATAF1 (Arabidopsis Transcription Activation Factor 1), which regulates biotic and abiotic stress responses. GmNAC109 protein localized to the nucleus and its C-terminal domain exhibited transcriptional activation activity. Salt, dehydration, and cold stresses significantly increased expression of GmNAC109 in soybean. Similarly, Arabidopsis plants overexpressing GmNAC109 were more tolerant to drought and salt stress than wild-type Col-0 plants. Stress response-related genes, such as DREB1A (drought-responsive element-binding 1A), DREB2A, AREB1 (ABSCISIC ACID-RESPONSIVE ELEMENT BINDING PROTEIN 1), AREB2, RD29A (RESPONSIVE TO Desiccation 29A), and COR15A (COLD REGULATED 15A) were upregulated in GmNAC109-overexpressing transgenic Arabidopsis lines. The transgenic lines showed upregulation of the ABA-responsive genes ABI1 (ABA INSENSITIVE 1) and ABI5 and hypersensitivity to ABA. However, GmNAC109 did not increase expression of the ABA-biosynthetic gene NCED3 (NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3) and endogenous ABA content in the transgenic lines. Overexpression of GmNAC109 significantly increased lateral root formation in transgenic Arabidopsis lines. Expression of AIR3 (AUXIN-INDUCED IN ROOT CULTURES 3) and ARF2 (AUXIN RESPONSE FACTOR 2) was increased and decreased in these transgenic lines, respectively, indicating that GmNAC109 is involved in the auxin signaling pathway and thereby helps to regulate hairy root formation. Our results provide a basis for development of soybean lines with improved tolerance to abiotic stresses via genetic manipulation.

Arabidopsis thaliana NGATHA1 transcription factor induces ABA biosynthesis by activating NCED3 gene during dehydration stress

The plant hormone abscisic acid (ABA) is accumulated after drought stress and plays critical roles in the responses to drought stress in plants, such as gene regulation, stomatal closure, seed maturation, and dormancy. Although previous reports revealed detailed molecular roles of ABA in stress responses, the factors that contribute to the drought-stress responses-in particular, regulation of ABA accumulation-remain unclear. The enzyme NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) is essential for ABA biosynthesis during drought stress, and the NCED3 gene is highly induced by drought stress. In the present study, we isolated NGATHAs (NGAs) as candidate transcriptional regulators of NCED3 through a screen of a plant library harboring the transcription factors fused to a chimeric repressor domain, SRDX. The NGA proteins were directly bound to a cis-element NGA-binding element (NBE) in the 5' untranslated region (5' UTR) of the NCED3 promoter and were suggested to be transcriptional activators of NCED3 Among the single-knockout mutants of four NGA family genes, we found that the NGATHA1 (NGA1) knockout mutant was drought-stress-sensitive with a decreased expression level of NCED3 during dehydration stress. These results suggested that NGA1 essentially functions as a transcriptional activator of NCED3 among the NGA family proteins. Moreover, the NGA1 protein was degraded under nonstressed conditions, and dehydration stress enhanced the accumulation of NGA1 proteins, even in ABA-deficient mutant plants, indicating that there should be ABA-independent posttranslational regulations. These findings emphasize the regulatory mechanisms of ABA biosynthesis during early drought stress.

Prevention of Preharvest Sprouting through Hormone Engineering and Germination Recovery by Chemical Biology.

Vivipary, germination of seeds on the maternal plant, is observed in nature and provides ecological advantages in certain wild species, such as mangroves. However, precocious seed germination in agricultural species, such as preharvest sprouting (PHS) in cereals, is a serious issue for food security. PHS reduces grain quality and causes economical losses to farmers. PHS can be prevented by translating the basic knowledge of hormone biology in seeds into technologies. Biosynthesis of abscisic acid (ABA), which is an essential hormone for seed dormancy, can be engineered to enhance dormancy and prevent PHS. Enhancing nine-cis-epoxycarotenoid dioxygenase (NCED), a rate-limiting enzyme of ABA biosynthesis, through a chemically induced gene expression system, has successfully been used to suppress germination of Arabidopsis seeds. The more advanced system NCED positive-feedback system, which amplifies ABA biosynthesis in a seed-specific manner without chemical induction, has also been developed. The proofs of concept established in the model species are now ready to be applied to crops. A potential problem is recovery of germination from hyperdormant crop grains. Hyperdormancy induced by the NCED systems can be reversed by inducing counteracting genes, such as NCED RNA interference or gibberellin (GA) biosynthesis genes. Alternatively, seed sensitivity to ABA can be modified to rescue germination using the knowledge of chemical biology. ABA antagonists, which were developed recently, have great potential to recover germination from the hyperdormant seeds. Combination of the dormancy-imposing and -releasing approaches will establish a comprehensive technology for PHS prevention and germination recovery.

Dissection of Arabidopsis NCED9 promoter regulatory regions reveals a role for ABA synthesized in embryos in the regulation of GA-dependent seed germination

Nine-cis-epoxycarotenoid dioxygenase (NCED) catalyzes the key step of abscisic acid (ABA) biosynthesis. There are five genes encoding NCED in Arabidopsis, which differentially regulate ABA biosynthesis in a spatiotemporal manner in response to endogenous and environmental stimuli. Previous studies have shown that NCED9 is expressed in testa and embryos during seed development. In the present study, we have identified promoter regions required for the expression of NCED9 in testa and embryos, respectively. Electrophoretic mobility shift assays (EMSA) and yeast one-hybrid (Y1H) assays showed that several homeodomain-leucine zipper (HD-Zip) proteins, namely ATHBs, bound to the sequence required for expression of NCED9 in testa, suggesting that they redundantly regulate NCED9 expression. By expressing the NCED9 gene under the control of a deleted NCED9 promoter in an nced9 mutant expression was limited to embryos. Transformants were complemented for the paclobutrazol resistant germination phenotype of the mutant, suggesting that the ABA synthesis mediated by NCED9 in embryos plays an important role in the regulation of gibberellin (GA)-dependent seed germination.

Heavy metals and gene expression in plant stomata

Stomata are structures that regulate leaf gas exchange with the atmosphere, allowing the entrance of CO2 to promote photosynthesis and the exit of O2 as a byproduct. Many studies have documented the changes caused by environmental stress in the number of stomata on plant leaves and in the opening and closing of these plant structures. Opening and closing of stomata is regulated by environmental and physiological factors, such as hormones, however, many molecular and genetic details have not been revealed. The purpose of this research is to understand the genetic and molecular basis of the environmental stress on plant stomata. We are focused on the effect of heavy metals on the expression of the following genes from Arabidopsis thaliana: stomatal closure-related actin binding protein 1 (SCAB1), actin 2 (ACT2), myosin (MYOATP), metallothionein 2B (MT2B), and nine-cis-epoxycarotenoid dioxygenase 3 (NCED3). Plants were exposed to cadmium and total RNA from whole plant and plant stomata was isolate. Different bioinformatics tools were used to assess and identify specific oligonucleotide sequences for these genes. cDNA was obtained and gene expression was determined by real time PCR. Preliminary results showed changes in the expression of SCAB1, ACT2, MYOATP, MT2B and NCED3 due to exposure to cadmium. Experiments are underway to establish a relationship between the opening and closing of stomata due exposition to cadmium.

Physiological and transcriptional memory in guard cells during repetitive dehydration stress.

Arabidopsis plants subjected to a daily dehydration stress and watered recovery cycle display physiological and transcriptional stress memory. Previously stressed plants have stomatal apertures that remain partially closed during a watered recovery period, facilitating reduced transpiration during a subsequent dehydration stress. Guard cells (GCs) display transcriptional memory that is similar to that in leaf tissues for some genes, but display GC-specific transcriptional memory for other genes. The rate-limiting abscisic acid (ABA) biosynthetic genes NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) and ALDEHYDE OXIDASE 3 (AAO3) are expressed at much higher levels in GCs, particularly during the watered recovery interval, relative to their low levels in leaves. A genetic analysis using mutants in the ABA signaling pathway indicated that GC stomatal memory is ABA-dependent, and that ABA-dependent SNF1-RELATED PROTEIN KINASE 2.2 (SnRK2.2), SnRK2.3 and SnRK2.6 have distinguishable roles in the process. SnRK2.6 is more important for overall stomatal control, while SnRK2.2 and SnRK2.3 are more important for implementing GC stress memory in the subsequent dehydration response. Collectively, our results support a model of altered ABA production in GCs that maintains a partially closed stomatal aperture during an overnight watered recovery period.

Abscisic Acid Regulates Axillary Bud Outgrowth Responses to the Ratio of Red to Far-Red Light

Low red light/far-red light ratio (R:FR) serves as an indicator of impending competition and has been demonstrated to suppress branch development. The regulation of Arabidopsis (Arabidopsis thaliana) rosette bud outgrowth by the R:FR and the associated mechanisms were investigated at several levels. Growth under low R:FR suppressed outgrowth of the third from topmost bud (bud n-2) but not that of the topmost bud. Subsequently increasing the R:FR near the time of anthesis promoted bud n-2 outgrowth and reduced topmost bud growth. Buds from specific rosette positions, exhibiting divergent fates to increased R:FR, were harvested 3 h after modifying the R:FR and were used to conduct ATH1 microarray-based transcriptome profiling. Differentially expressed genes showed enrichment of light signaling and hormone-related Gene Ontology terms and promoter motifs, most notably those associated with abscisic acid (ABA). Genes associated with ABA biosynthesis, including the key biosynthetic gene NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3 (NCED3), and with ABA signaling were expressed at higher levels in the responsive bud n-2, and increasing the R:FR decreased their expression only in bud n-2. ABA abundance in responsive buds decreased within 12 h of increasing the R:FR, while indole-3-acetic acid levels did not change. A role for ABA in repressing bud outgrowth from lower positions under low R:FR was demonstrated using the nced3-2 and aba2-1 ABA biosynthesis mutants, which showed enhanced branching and a defective bud n-2 outgrowth response to low R:FR. The results provide evidence that ABA regulates bud outgrowth responses to the R:FR and thus extend the known hormonal pathways associated with the regulation of branching and shade avoidance.

Abamine as a basis for new designs of regulators of strigolactone production

Nine-cis-epoxycarotenoid dioxygenase (NCED), belonging to the family of carotenoid-cleaving dioxygenases (CCDs), is the rate-limiting step in the abscisic acid (ABA) biosynthetic pathway in plants. Abamine is the first reported abscisic acid biosynthesis inhibitor to target NCED. Its utility has also been considered in the inhibition of other enzymes. As CCDs other than NCED are also involved in the strigolactone biosynthetic pathway, abamine may affect strigolactone biosynthesis. In this study, we found that abamine decreases the level of strigolactones in several plant species and reduces the germination rate of Orobanche minor seeds co-grown with tobacco. Taken together, these data suggest that abamine may be used as a scaffold for the development of specific regulators of strigolactone production.

English

Abscisic acid (ABA) plays an important role in seed dormancy, embryo development and adaptation to environmental stresses. We found that imbibition of exogenous ABA by peanut seeds led to a significant increase in the levels of bothAhNCED1 gene [a key gene encoding nine-cis-epoxycarotenoid dioxygenase (NCED) involved in ABA biosynthesis in peanut] transcript and endogenous ABA in germinating seeds, and also led to a marked decrease in α-amylase activity, germination rate and viability index of germinating seeds. This was associated morphogenetically with inhibited plumule apex growth and reduced leaf primordium elongation, a decreased number and length of axial and lateral buds, and shorter length of compound leaves during germination. Imbibition by peanut seeds of naproxen (a potent ABA biosynthesis inhibitor specifically targeting to NCED) significantly decreased the levels of endogenous ABA and AhNCED1 gene transcript in germinating seeds, and markedly increased α-amylase activity, germination rate and viability index of germinating seeds. This was associated morphogenetically with increased plumule apex growth and leaf primordium elongation as well as increased number and length of axial and lateral buds, but without a significant change in the length of compound leaves during seed germination. These observations suggest the involvement of a positive feedback regulation of ABA biosynthesis in ABA-mediated inhibition of seed germination in peanut.   Key words: Abscisic acid, AhNCED1 gene, biosynthesis, feedback regulation, peanut (Arachis hypogaea L.), seed germination.