Expression of ethylene biosynthetic pathway transcripts in senescing carnation flowers

Shade stress triggers ethylene biosynthesis to accelerate soybean senescence and impede nitrogen remobilization

In gramineae-soybean intercropping systems, shade stress caused by taller plants impacts soybean growth specifically during the reproductive stage. However, the effects of shade stress on soybean senescence remain largely unexplored. In this research, we applied artificial shade treatments with intensities of 75% (S75) and 50% (S50) to soybean plants at the onset of flowering to simulate the shade stress experienced by soybeans in the traditional and optimized maize-soybean intercropping systems, respectively. Compared to the normal light control, both shade treatments led to a rapid decline in the dry matter content of soybean vegetative organs and accelerated their abscission. Moreover, shade treatments triggered the degradation of chlorophyll and soluble proteins in leaves and increased the expression of genes associated with leaf senescence. Metabolic profiling further revealed that ethylene biosynthesis and signal transduction were induced by shade treatment. In addition, the examination of nitrogen content demonstrated that shade treatments impeded the remobilization of nitrogen in vegetative tissues, consequently reducing the seed nitrogen harvest. It's worth noting that these negative effects were less pronounced under the S50 treatment compared to the S75 treatment. Taken together, this research demonstrates that shade stress during the reproductive stage accelerates soybean senescence and impedes nitrogen remobilization, while optimizing the field layout to improve soybean growth light conditions could mitigate these challenges in the maize-soybean intercropping system.

Transcriptomic and Metabolic Profiling Reveal the Mechanism of Ovule Development in Castanea mollissima

Ovule abortion, which is the main cause of empty burs in the Chinese chestnut, affects the formation of embryos and further reduces yield; therefore, it is important to study the mechanism of ovule abortion. In this study, we analyzed the transcriptomic and metabolomic data of ovules at critical developmental stages to explore the key regulatory networks affecting ovule development. The metabolites were enriched mainly in pathways involved in phytohormone signaling, energy metabolism, and amino acid synthesis in the endoplasmic reticulum. Analysis of the differentially expressed genes (DEGs) revealed that the HSP genes were significantly down-regulated during fertilization, indicating that this process is extremely sensitive to temperature. The hormone and sucrose contents of ovules before and after fertilization and of fertile and abortive ovules at different developmental stages showed significant differences, and it is hypothesized that that abnormal temperature may disrupt hormone synthesis, affecting the synthesis and catabolism of sucrose and ultimately resulting in the abortive development of Chinese chestnut ovules. At the pollination and fertilization stage of chestnuts, spraying with ethylene, ACC, and AIB significantly increased the number of developing fruit in each prickly pod compared to CK (water) treatment. These results indicated that both ethylene and ACC increased the rate of ovule development. This study provides an important theoretical molecular basis for the subsequent regulation of ovule development and nut yield in the Chinese chestnut.

Histone H3K4 methyltransferase DcATX1 promotes ethylene induced petal senescence in carnation

Petal senescence is controlled by a complex regulatory network. Epigenetic regulation like histone modification influences chromatin state and gene expression. However, the involvement of histone methylation in regulating petal senescence remains poorly understood. Here, we found that the trimethylation of histone H3 at Lysine 4 (H3K4me3) is increased during ethylene-induced petal senescence in carnation (Dianthus caryophyllus L.). H3K4me3 levels were positively associated with the expression of transcription factor DcWRKY75, ethylene biosynthetic genes 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (DcACS1), and ACC oxidase (DcACO1), and senescence associated genes (SAGs) DcSAG12 and DcSAG29. Further, we identified that carnation ARABIDOPSIS HOMOLOG OF TRITHORAX1 (DcATX1) encodes a histone lysine methyltransferase which can methylate H3K4. Knockdown of DcATX1 delayed ethylene-induced petal senescence in carnation, which was associated with the down-regulated expression of DcWRKY75, DcACO1, and DcSAG12, whereas overexpression of DcATX1 exhibited the opposite effects. DcATX1 promoted the transcription of DcWRKY75, DcACO1, and DcSAG12 by elevating the H3K4me3 levels within their promoters. Overall, our results demonstrate that DcATX1 is a H3K4 methyltransferase that promotes the expression of DcWRKY75, DcACO1, DcSAG12 and potentially other downstream target genes by regulating H3K4me3 levels, thereby accelerating ethylene-induced petal senescence in carnation. This study further indicates that epigenetic regulation is important for plant senescence processes.

TMT-based proteomic analysis of liquorice root in response to drought stress

BACKGROUND

Drought stress is a serious threat to land use efficiency and crop yields worldwide. Understanding the mechanisms that plants use to withstand drought stress will help breeders to develop drought-tolerant medicinal crops. Liquorice (Glycyrrhiza uralensis Fisch.) is an important medicinal crop in the legume family and is currently grown mostly in northwest China, it is highly tolerant to drought. Given this, it is considered an ideal crop to study plant stress tolerance and can be used to identify drought-resistant proteins. Therefore, to understand the effects of drought stress on protein levels of liquorice, we undertook a comparative proteomic analysis of liquorice seedlings grown for 10 days in soil with different relative water content (SRWC of 80%, 65%, 50% and 35%, respectively). We used an integrated approach of Tandem Mass Tag labeling in conjunction with LC-MS/MS.

RESULTS

A total of 7409 proteins were identified in this study, of which 7305 total proteins could be quantified. There were 837 differentially expressed proteins (DEPs) identified after different drought stresses. Compared with CK, 123 DEPs (80 up-regulated and 43 down-regulated) were found in LS; 353 DEPs (254 up-regulated and 99 down-regulated) in MS; and 564 DEPs (312 up-regulated and 252 down-regulated) in SS.The number of differentially expressed proteins increased with increasing water stress, and the number of up-regulated proteins was higher than that of down-regulated proteins in the different drought stress treatments compared with the CK. Used systematic bioinformatics analysis of these data to identify informative proteins we showed that osmolytes such as cottonseed sugars and proline accumulated under light drought stress and improved resistance. Under moderate and severe drought stress, oxidation of unsaturated fatty acids and accumulation of glucose and galactose increased in response to drought stress. Under moderate and severe drought stress synthesis of the terpene precursors, pentacene 2,3-epoxide and β-coumarin, was inhibited and accumulation of triterpenoids (glycyrrhetinic acid) was also affected.

CONCLUSIONS

These data provide a baseline reference for further study of the downstream liquorice proteome in response to drought stress. Our data show that liquorice roots exhibit specific response mechanisms to different drought stresses.

DcWRKY75 promotes ethylene induced petal senescence in carnation (Dianthus caryophyllus L.)

Carnation (Dianthus caryophyllus L.) is one of the most important and typical ethylene sensitive cut flowers worldwide, although how ethylene influences the petal senescence process in carnation remains largely unknown. Here, we screened out one of the key transcription factors, DcWRKY75, using a constructed ethylene induced petal senescence transcriptome in carnation and found that it shows quick induction by ethylene treatment. Silencing of DcWRKY75 delays ethylene induced petal senescence in carnation. Molecular evidence confirms that DcWRKY75 can bind to the promoter regions of two main ethylene biosynthetic genes (DcACS1 and DcACO1) and a couple of senescence associated genes (DcSAG12 and DcSAG29) to activate their expression. Furthermore, we show that DcWRKY75 is a direct target gene of DcEIL3-1, which is a homolog of the ethylene signaling core transcription factor EIN3 in Arabidopsis. DcEIL3-1 can physically interact with DcWRKY75 and silencing of DcEIL3-1 also delays ethylene induced petal senescence in carnation and inhibits the ethylene induced expression of DcWRKY75 and its target genes. The present study demonstrates that the transcriptional regulation network is vitally important for ethylene induced petal senescence process in carnation and potentially in other ethylene sensitive cut flowers.

Can gene editing reduce postharvest waste and loss of fruit, vegetables, and ornamentals?

Postharvest waste and loss of horticultural crops exacerbates the agricultural problems facing humankind and will continue to do so in the next decade. Fruits and vegetables provide us with a vast spectrum of healthful nutrients, and along with ornamentals, enrich our lives with a wide array of pleasant sensory experiences. These commodities are, however, highly perishable. Approximately 33% of the produce that is harvested is never consumed since these products naturally have a short shelf-life, which leads to postharvest loss and waste. This loss, however, could be reduced by breeding new crops that retain desirable traits and accrue less damage over the course of long supply chains. New gene-editing tools promise the rapid and inexpensive production of new varieties of crops with enhanced traits more easily than was previously possible. Our aim in this review is to critically evaluate gene editing as a tool to modify the biological pathways that determine fruit, vegetable, and ornamental quality, especially after storage. We provide brief and accessible overviews of both the CRISPR-Cas9 method and the produce supply chain. Next, we survey the literature of the last 30 years, to catalog genes that control or regulate quality or senescence traits that are "ripe" for gene editing. Finally, we discuss barriers to implementing gene editing for postharvest, from the limitations of experimental methods to international policy. We conclude that in spite of the hurdles that remain, gene editing of produce and ornamentals will likely have a measurable impact on reducing postharvest loss and waste in the next 5-10 years.

The regulation of ethylene biosynthesis: a complex multilevel control circuitry

The gaseous plant hormone ethylene is produced by a fairly simple two-step biosynthesis route. Despite this pathway's simplicity, recent molecular and genetic studies have revealed that the regulation of ethylene biosynthesis is far more complex and occurs at different layers. Ethylene production is intimately linked with the homeostasis of its general precursor S-adenosyl-l-methionine (SAM), which experiences transcriptional and posttranslational control of its synthesising enzymes (SAM synthetase), as well as the metabolic flux through the adjacent Yang cycle. Ethylene biosynthesis continues from SAM by two dedicated enzymes: 1-aminocyclopropane-1-carboxylic (ACC) synthase (ACS) and ACC oxidase (ACO). Although the transcriptional dynamics of ACS and ACO have been well documented, the first transcription factors that control ACS and ACO expression have only recently been discovered. Both ACS and ACO display a type-specific posttranslational regulation that controls protein stability and activity. The nonproteinogenic amino acid ACC also shows a tight level of control through conjugation and translocation. Different players in ACC conjugation and transport have been identified over the years, however their molecular regulation and biological significance is unclear, yet relevant, as ACC can also signal independently of ethylene. In this review, we bring together historical reports and the latest findings on the complex regulation of the ethylene biosynthesis pathway in plants.

Nano-silver modifies the vase life of cut herbaceous peony (Paeonia lactiflora Pall.) flowers

Herbaceous peony (Paeonia lactiflora Pall.) is a popular high-grade cut flower because of higher ornamental value. However, its short flowering time severely restricts the production and application of cut P. lactiflora flowers. In this study, nano-silver (NS) was applied to prolong the vase life of cut P. lactiflora flowers. Under the NS treatment, related physiological indices including relative electrical conductivity (REC), malondialdehyde (MDA), superoxide anion free radical (O₂^·-), hydrogen peroxide (H₂O₂) and free proline contents, and protective enzyme activities including superoxide dismutase (SOD), peroxidase (POD) and ascorbic acid peroxidase (APX) all increased in cut P. lactiflora flowers except soluble protein. Meanwhile, NS treatment increased relative water uptake (RWU) and Ag⁺ distribution. Moreover, the observation of microstructures indicated that the stem-ends without NS treatment were blocked by microbes which were identified as Alternaria sp. and Phoma sp., and NS effectively inhibited their growth by antibacterial efficacy observation. Additionally, three aquaporin genes (AQPs) including two plasma membrane intrinsic protein genes (PlPIP1;2, PlPIP2;1) and one NOD26-like intrinsic protein gene (PlNIP) were isolated, PlPIP1;2, and PlPIP2;1 that were induced by NS treatment took common effects on maintaining the water balance of cut P. lactiflora flowers. Consequently, the vase life of cut P. lactiflora flowers was prolonged and flower fresh weight together with flower diameter was well kept because of these above factors. These results would provide a theoretical basis for prolonging the vase life and improving the ornamental quality of cut P. lactiflora flowers with NS application.

Escherichia coli-Based Expression and In Vitro Activity Assay of 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase and ACC Oxidase

1-Aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase are key enzymes in the ethylene biosynthetic pathway in plant tissues, and in vitro assay of their activities is indispensable for analysis, especially, for studying the action mechanism of inhibitors of ethylene biosynthesis. The enzymes can be obtained from plant tissues that are producing ethylene abundantly, such as ripening fruit- and senescing flower tissues, but it is necessary to separate the enzymes from co-extracted ACC by partial purification, making the procedure laborious and time-consuming. Here, we describe the production of the enzymes in Escherichia coli cells from corresponding cDNAs, and the procedures for assay of activities of the enzymes.

Proteomic Identification of Differentially Expressed Proteins during Alfalfa (Medicago sativa L.) Flower Development

Flower development, pollination, and fertilization are important stages in the sexual reproduction process of plants; they are also critical steps in the control of seed formation and development. During alfalfa (Medicago sativa L.) seed production, some distinct phenomena such as a low seed setting ratio, serious flower falling, and seed abortion commonly occur. However, the causes of these phenomena are complicated and largely unknown. An understanding of the mechanisms that regulate alfalfa flowering is important in order to increase seed yield. Hence, proteomic technology was used to analyze changes in protein expression during the stages of alfalfa flower development. Flower samples were collected at pre-pollination (S1), pollination (S2), and the post-pollination senescence period (S3). Twenty-four differentially expressed proteins were successfully identified, including 17 down-regulated in pollinated flowers, one up-regulated in pollinated and senesced flowers, and six up-regulated in senesced flowers. The largest proportions of the identified proteins were involved in metabolism, signal transduction, defense response, oxidation reduction, cell death, and programmed cell death (PCD). Their expression profiles demonstrated that energy metabolism, carbohydrate metabolism, and amino acid metabolism provided the nutrient foundation for pollination in alfalfa. Furthermore, there were three proteins involved in multiple metabolic pathways: dual specificity kinase splA-like protein (kinase splALs), carbonic anhydrase, and NADPH: quinone oxidoreductase-like protein. Expression patterns of these proteins indicated that MAPK cascades regulated multiple processes, such as signal transduction, stress response, and cell death. PCD also played an important role in the alfalfa flower developmental process, and regulated both pollination and flower senescence. The current study sheds some light on protein expression profiles during alfalfa flower development and contributes to the understanding of the basic molecular mechanisms during the alfalfa flowering process. These results may offer insight into potential strategies for improving seed yield, quality, and stress tolerance in alfalfa.

Molecular cloning and expression analysis of an 1-aminocyclopropane-1-carboxylate synthase gene from Oncidium Gower Ramsey

1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) is a rate-limiting enzyme in the biosynthesis of ethylene which regulates many aspects of the plant development and responses to biotic and abiotic stresses. In this study, a full-length cDNA of ACC synthase, OnACS2, was cloned from the senescing flower of Oncidium Gower Ramsey by RACE. The full-length cDNA of OnACS2 (GenBank accession no. JQ822087) was 1557 bp in length with an open reading frame (ORF) of 1308 bp encoding for a protein of 435 amino acid residues. The predicted OnACS2 protein had a molecular mass of 49.1 kDa with pI value of 7.51. Phylogenetic analysis indicated its evolutionary relationships with corresponding orthologous sequences in orchids, Hosta ventricosa and monocots. Real-time PCR assay demonstrated that OnACS2 was constitutively expressed in all tested organs with the highest transcript level in the gynandria. Differential expression pattern of OnACS2 gene correlated to the ethylene production and the subsequent occurrence of senescent symptoms in flower suggested that OnACS2 probably played an important role in the initiation of flower senescence.

Ethylene resistance in flowering ornamental plants - improvements and future perspectives

Various strategies of plant breeding have been attempted in order to improve the ethylene resistance of flowering ornamental plants. These approaches span from conventional techniques such as simple cross-pollination to new breeding techniques which modify the plants genetically such as precise genome-editing. The main strategies target the ethylene pathway directly; others focus on changing the ethylene pathway indirectly via pathways that are known to be antagonistic to the ethylene pathway, e.g. increasing cytokinin levels. Many of the known elements of the ethylene pathway have been addressed experimentally with the aim of modulating the overall response of the plant to ethylene. Elements of the ethylene pathway that appear particularly promising in this respect include ethylene receptors as ETR1, and transcription factors such as EIN3. Both direct and indirect approaches seem to be successful, nevertheless, although genetic transformation using recombinant DNA has the ability to save much time in the breeding process, they are not readily used by breeders yet. This is primarily due to legislative issues, economic issues, difficulties of implementing this technology in some ornamental plants, as well as how these techniques are publically perceived, particularly in Europe. Recently, newer and more precise genome-editing techniques have become available and they are already being implemented in some crops. New breeding techniques may help change the current situation and pave the way toward a legal and public acceptance if products of these technologies are indistinguishable from plants obtained by conventional techniques.

A basic helix-loop-helix transcription factor, PhFBH4, regulates flower senescence by modulating ethylene biosynthesis pathway in petunia

The basic helix-loop-helix (bHLH) transcription factors (TFs) play important roles in regulating multiple biological processes in plants. However, there are few reports about the function of bHLHs in flower senescence. In this study, a bHLH TF, PhFBH4, was found to be dramatically upregulated during flower senescence. Transcription of PhFBH4 is induced by plant hormones and abiotic stress treatments. Silencing of PhFBH4 using virus-induced gene silencing or an antisense approach extended flower longevity, while transgenic petunia flowers with an overexpression construct showed a reduction in flower lifespan. Abundance of transcripts of senescence-related genes (SAG12, SAG29) was significantly changed in petunia PhFBH4 transgenic flowers. Furthermore, silencing or overexpression of PhFBH4 reduced or increased, respectively, transcript abundances of important ethylene biosynthesis-related genes, ACS1 and ACO1, thereby influencing ethylene production. An electrophoretic mobility shift assay showed that the PhFBH4 protein physically interacted with the G-box cis-element in the promoter of ACS1, suggesting that ACS1 was a direct target of the PhFBH4 protein. In addition, ectopic expression of this gene altered plant development including plant height, internode length, and size of leaves and flowers, accompanied by alteration of transcript abundance of the gibberellin biosynthesis-related gene GA2OX3. Our results indicate that PhFBH4 plays an important role in regulating plant growth and development through modulating the ethylene biosynthesis pathway.

Shedding light on ethylene metabolism in higher plants

Ethylene metabolism in higher plants is regulated by a wide array of endogenous and environmental factors. During most physiological processes, ethylene levels are mainly determined by a strict control of the rate-limiting biosynthetic steps responsible for the production of 1-aminocyclopropane-1-carboxylic acid (ACC) and its subsequent conversion to ethylene. Responsible for these reactions, the key enzymes ACC synthase and ACC oxidase are encoded by multigene families formed by members that can be differentially regulated at the transcription and post-translational levels by specific developmental and environmental signals. Among the wide variety of environmental cues controlling plant ethylene production, light quality, duration, and intensity have consistently been demonstrated to influence the metabolism of this plant hormone in diverse plant tissues, organs, and species. Although still not completely elucidated, the mechanisms underlying the interaction between light signal transduction and ethylene evolution appears to involve a complex network that includes central transcription factors connecting multiple signaling pathways, which can be reciprocally modulated by ethylene itself, other phytohormones, and specific light wavelengths. Accumulating evidence has indicated particular photoreceptors as essential mediators in light-induced signaling cascades affecting ethylene levels. Therefore, this review specifically focuses on discussing the current knowledge of the potential molecular mechanisms implicated in the light-induced responses affecting ethylene metabolism during the regulation of developmental and metabolic plant responses. Besides presenting the state of the art in this research field, some overlooked mechanisms and future directions to elucidate the exact nature of the light-ethylene interplay in higher plants will also be compiled and discussed.

Ethylene production associated with petal senescence in carnation flowers is induced irrespective of the gynoecium

To clarify whether climacteric-like increases in ethylene production of senescing petals are also induced in the absence of the gynoecium in cut carnation (Dianthus caryophyllus cv. Barbara) flowers, we compared ethylene production and expression of ethylene-biosynthesis genes in detached petals and in petals, which remained on flowers (attached petals). No significant difference in longevity was observed between the attached and detached petals when held in distilled water, and both showed the inward rolling typical of senescing flowers. Treatment with silver thiosulfate complex (STS), an ethylene inhibitor, similarly delayed senescence of attached and detached petals. Climacteric-like increases in ethylene production of petals and gynoecium started on the same day, with similar bursts in attached and detached petals. Transcript levels of DcACS1 and DcACO1 were very low at harvest and increased similarly during senescence in both petal groups. Removal of the gynoecium did not significantly delay wilting of attached petals. In flowers with the gynoecium removed, the petals produced most of the ethylene while production by the other floral organs was very low, suggesting that wound-induced ethylene is not the reason for the ineffectiveness of gynoecium-removal in inhibiting flower senescence. These results indicate that ethylene biosynthesis is induced in carnation petals irrespective of the gynoecium.

Precise spatio-temporal modulation of ACC synthase by MPK6 cascade mediates the response of rose flowers to rehydration

Drought is a major abiotic stress that affects the development and growth of most plants, and limits crop yield worldwide. Although the response of plants to drought has been well documented, much less is known about how plants respond to the water recovery process, namely rehydration. Here, we describe the spatio-temporal response of plant reproductive organs to rehydration using rose flowers as an experimental system. We found that rehydration triggered rapid and transient ethylene production in the gynoecia. This ethylene burst serves as a signal to ensure water recovery in flowers, and promotes flower opening by influencing the expression of a set of rehydration-responsive genes. An in-gel kinase assay suggested that the rehydration-induced ethylene burst resulted from transient accumulation of RhACS1/2 proteins in gynoecia. Meanwhile, RhMPK6, a rose homolog of Arabidopsis thaliana MPK6, is rapidly activated by rehydration within 0.5 h. Furthermore, RhMPK6 was able to phosphorylate RhACS1 but not RhACS2 in vitro. Application of the kinase inhibitor K252a suppressed RhACS1 accumulation and rehydration-induced ethylene production in gynoecia, and the protein phosphatase inhibitor okadaic acid had the opposite effect, confirming that accumulation of RhACS1 was phosphorylation-dependent. Finally, silencing of RhMPK6 significantly reduced ethylene production in gynoecia when flowers were subjected to rehydration. Taken together, our results suggest that temporal- and spatial-specific activation of an RhMPK6-RhACS1 cascade is responsible for rehydration-induced ethylene production in gynoecia, and that the resulting ethylene-mediated signaling pathway is a key factor in flower rehydration.

Comparative proteome analysis of the response of ramie under N, P and K deficiency

Ramie is an important natural fiber. There has been little research on the molecular mechanisms of ramie related to the absorption, utilization and metabolism of nitrogen (N), phosphorus (P) and potassium (K). One approach to reveal the mechanisms of N, P and K (NPK) utilization and metabolism in ramie is comparative proteome analysis. The differentially expressed proteins in the leaves of ramie were analyzed by proteome analysis after 6 days of N- and K-deficient treatments and 3 days of P-deficient treatment using MALDI-TOF/TOF mass spectrometry and 32, 27 and 51 differential proteins were obtained, respectively. These proteins were involved in photosynthesis, protein destination and storage, energy metabolism, primary metabolism, disease/defense, signal transduction, cell structure, transcription, secondary metabolism and protein synthesis. Ramie responded to NPK stress by enhancing secondary metabolism and reducing photosynthesis and energy metabolism to increase endurance. Specifically, ramie adapted to NPK deficiency by increasing signal transduction pathways, enhancing the connection between glycolysis and photosynthesis, promoting the intracellular flow of carbon and N; promoting the synthesis cysteine and related hormones and upregulating actin protein to promote growth of the root system. The experimental results provide important information for further study on the high-efficiency NPK utilization mechanism of ramie.

Analysis of gene expression during the transition to climacteric phase in carnation flowers (Dianthus caryophyllus L.)

It has been generally thought that in ethylene-sensitive plants such as carnations, senescence proceeds irreversibly once the tissues have entered the climacteric phase. While pre-climacteric petal tissues have a lower sensitivity to ethylene, these tissues are converted to the climacteric phase at a critical point during flower development. In this study, it is demonstrated that the senescence process initiated by exogenous ethylene is reversible in carnation petals. Petals treated with ethylene for 12h showed sustained inrolling and senescence, while petals treated with ethylene for 10h showed inrolling followed by recovery from inrolling. Reverse transcription-PCR analysis revealed differential expression of genes involved in ethylene biosynthesis and ethylene signalling between 10h and 12h ethylene treatment. Ethylene treatment at or beyond 12h (threshold time) decreased the mRNA levels of the receptor genes (DcETR1, DcERS1, and DcERS2) and DcCTR genes, and increased the ethylene biosynthesis genes DcACS1 and DcACO1. In contrast, ethylene treatment under the threshold time caused a transient decrease in the receptor genes and DcCTR genes, and a transient increase in DcACS1 and DcACO1. Sustained DcACS1 accumulation is correlated with decreases in DcCTR genes and increase in DcEIL3 and indicates that tissues have entered the climacteric phase and that senescence proceeds irreversibly. Inhibition of ACS (1-aminocyclopropane-1-carboxylic acid synthase) prior to 12h ethylene exposure was not able to prevent reduction in transcripts of DcCTR genes, yet suppressed transcript of DcACS1 and DcACO1. This leads to the recovery from inrolling of the petals, indicating that DcACS1 may act as a signalling molecule in senescence of flowers.

The Antioxidants Changes in Ornamental Flowers during Development and Senescence

The concentration of antioxidant compounds is constitutive and variable from species to species and is also variable considering the development of the plant tissue. In this review, we take into consideration the antioxidant changes and the physiological, biochemical and molecular factors that are able to modulate the accumulation of antioxidant compounds in ornamental flowers during the whole development process until the senescence. Many ornamental flowers are natural sources of very important bioactive compounds with benefit to the human health and their possible role as dietary components has been reported. The most part of antioxidants are flower pigments such as carotenoids and polyphenols, often present in higher concentration compared with the most common fruits and vegetables. The antioxidants content changes during development and during senescence many biochemical systems and molecular mechanisms are activated to counteract the increase of reactive oxygen species and free radicals. There is a tight correlation between antioxidants and senescence processes and this aspect is detailed and appropriately discussed.

Dimethyl disulfide produced by the naturally associated bacterium bacillus sp B55 promotes Nicotiana attenuata growth by enhancing sulfur nutrition

Bacillus sp B55, a bacterium naturally associated with Nicotiana attenuata roots, promotes growth and survival of wild-type and, particularly, ethylene (ET)-insensitive (35)S-ethylene response1 (etr1) N. attenuata plants, which heterologously express the mutant Arabidopsis thaliana receptor ETR1-1. We found that the volatile organic compound (VOC) blend emitted by B55 promotes seedling growth, which is dominated by the S-containing compound dimethyl disulfide (DMDS). DMDS was depleted from the headspace during cocultivation with seedlings in bipartite Petri dishes, and (35)S was assimilated from the bacterial VOC bouquet and incorporated into plant proteins. In wild-type and (35)S-etr1 seedlings grown under different sulfate (SO(4)(-2)) supply conditions, exposure to synthetic DMDS led to genotype-dependent plant growth promotion effects. For the wild type, only S-starved seedlings benefited from DMDS exposure. By contrast, growth of (35)S-etr1 seedlings, which we demonstrate to have an unregulated S metabolism, increased at all SO(4)(-2) supply rates. Exposure to B55 VOCs and DMDS rescued many of the growth phenotypes exhibited by ET-insensitive plants, including the lack of root hairs, poor lateral root growth, and low chlorophyll content. DMDS supplementation significantly reduced the expression of S assimilation genes, as well as Met biosynthesis and recycling. We conclude that DMDS by B55 production is a plant growth promotion mechanism that likely enhances the availability of reduced S, which is particularly beneficial for wild-type plants growing in S-deficient soils and for (35)S-etr1 plants due to their impaired S uptake/assimilation/metabolism.

Ethylene emission and PR protein synthesis in ACC deaminase producing Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.) challenged with Ralstonia solanacearum under greenhouse conditions

Bacteria of genus Methylobacterium have been found to promote plant growth and regulate the level of ethylene in crop plants. This work is aimed to test the induction of defense responses in tomato against bacterial wilt by stress ethylene level reduction mediated by the ACC deaminase activity of Methylobacterium strains. Under greenhouse conditions, the disease index value in Methylobacterium sp. inoculated tomato plants was lower than control plants. Plants treated with Methylobacterium sp. challenge inoculated with Ralstonia solanacearum (RS) showed significantly reduced disease symptoms and lowered ethylene emission under greenhouse condition. The ACC and ACO (1-aminocyclopropane-1-carboxylate oxidase) accumulation in tomato leaves were significantly reduced with Methylobacterium strains inoculation. While ACC oxidase gene expression was found higher in plants treated with R. solanacearum than Methylobacterium sp. treatment, PR proteins related to induced systemic resistance like β-1,3-glucanase, PAL, PO and PPO were increased in Methylobacterium sp. inoculated plants. A significant increase in β-1,3-glucanase and PAL gene expression was found in all the Methylobacterium spp. treatments compared to the R. solanacearum treatment. This study confirms the activity of Methylobacterium sp. in increasing the defense enzymes by modulating the ethylene biosynthesis pathway and suggests the use of methylotrophic bacteria as potential biocontrol agents in tomato cultivation.

Labellum transcriptome reveals alkene biosynthetic genes involved in orchid sexual deception and pollination-induced senescence

One of the most remarkable pollination strategy in orchids biology is pollination by sexual deception, in which the modified petal labellum lures pollinators by mimicking the chemical (e.g. sex pheromones), visual (e.g. colour and shape/size) and tactile (e.g. labellum trichomes) cues of the receptive female insect species. The present study aimed to characterize the transcriptional changes occurring after pollination in the labellum of a sexually deceptive orchid (Ophrys fusca Link) in order to identify genes involved on signals responsible for pollinator attraction, the major goal of floral tissues. Novel information on alterations in the orchid petal labellum gene expression occurring after pollination demonstrates a reduction in the expression of alkene biosynthetic genes using O. fusca Link as the species under study. Petal labellum transcriptional analysis revealed downregulation of transcripts involved in both pigment machinery and scent compounds, acting as visual and olfactory cues, respectively, important in sexual mimicry. Regulation of petal labellum senescence was revealed by transcripts related to macromolecules breakdown, protein synthesis and remobilization of nutrients.

Salt stress induced proteome and transcriptome changes in sugar beet monosomic addition line M14

Sugar beet monosomic addition line M14 displays interesting phenotypes such as apomixis and salt stress tolerance. Here we reported proteomic and transcriptomic analysis of M14 leaves and roots under 500mM NaCl treatment for seven days. Proteins from control and treated samples were extracted and separated using two-dimensional difference gel electrophoresis (2D-DIGE). A total of 40 protein spots from leaf gels and 36 protein spots from root gels exhibited significant changes. Using mass spectrometry and database searching, 38 unique proteins in leaves and 29 unique proteins in roots were identified. The proteins included those involved in metabolism, protein folding, photosynthesis, and protein degradation. In addition, cDNA libraries of differentially expressed genes were constructed using suppression subtractive hybridization (SSH). Fifty-eight unigenes including 14 singletons and 44 contigs were obtained. Some salt-responsive genes were identified to function in metabolism, photosynthesis, stress and defense, energy, protein synthesis and protein degradation. This research has revealed candidate genes and proteins for detailed functional characterization, and set the stage for further investigation of the salt tolerance mechanisms in sugar beet.

Effects of abscisic acid on ethylene biosynthesis and perception in Hibiscus rosa-sinensis L. flower development

The effect of the complex relationship between ethylene and abscisic acid (ABA) on flower development and senescence in Hibiscus rosa-sinensis L. was investigated. Ethylene biosynthetic (HrsACS and HrsACO) and receptor (HrsETR and HrsERS) genes were isolated and their expression evaluated in three different floral tissues (petals, style-stigma plus stamens, and ovaries) of detached buds and open flowers. This was achieved through treatment with 0.1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) solution, 500 nl l(-1) methylcyclopropene (1-MCP), and 0.1 mM ABA solution. Treatment with ACC and 1-MCP confirmed that flower senescence in hibiscus is ethylene dependent, and treatment with exogenous ABA suggested that ABA may play a role in this process. The 1-MCP impeded petal in-rolling and decreased ABA content in detached open flowers after 9 h. This was preceded by an earlier and sequential increase in ABA content in 1-MCP-treated petals and style-stigma plus stamens between 1 h and 6 h. ACC treatment markedly accelerated flower senescence and increased ethylene production after 6 h and 9 h, particularly in style-stigma plus stamens. Ethylene evolution was positively correlated in these floral tissues with the induction of the gene expression of ethylene biosynthetic and receptor genes. Finally, ABA negatively affected the ethylene biosynthetic pathway and tissue sensitivity in all flower tissues. Transcript abundance of HrsACS, HrsACO, HrsETR, and HrsERS was reduced by exogenous ABA treatment. This research underlines the regulatory effect of ABA on the ethylene biosynthetic and perception machinery at a physiological and molecular level when inhibitors or promoters of senescence are exogenously applied.

Transcriptional regulation of two RTE-like genes of carnation during flower senescence and upon ethylene exposure, wounding treatment and sucrose supply

RTE1 (REVERSION-TO-ETHYLENE SENSITIVITY1) was identified as a positive regulator of ETR1 (ethylene resistant1) function in Arabidopsis; RTEs are a small gene family. Ethylene plays a crucial role in the senescence of carnation (Dianthus caryophyllus L.) flowers. Two cDNA clones encoding putative RTE-like protein (DCRTE1 and DCRTH1) were obtained from total RNA isolated from senescing carnation petals using RT-PCR and RACE techniques. The predicted proteins of DCRTE1 and DCRTH1 consist of 228 and 233 amino acids, respectively. Interestingly, the deduced DCRTE1 protein, like most other RTEs, includes two putative transmembrane domains, while the deduced DCRTH1 protein includes five putative transmembrane domains, according to the TMHMM database. Northern blots showed that the level of DCRTE1 mRNA in petals first decreased then increased remarkably after ethylene production started, and DCRTE1 expression showed an increasing trend in ovaries during natural flower senescence. The amount of DCRTH1 transcripts increased gradually in both petals and ovaries during natural senescence. Exogenous ethylene increased transcript abundance of DCRTE1 and DCRTH1 to various degrees in both petals and ovaries. STS treatment decreased the level of DCRTH1 mRNA in petals and ovaries compared with the control. DCRTE1 and DCRTH1 showed a rapid increase and then a decrease in mRNA accumulation in leaves after wounding. These results suggest that both DCRTE1 and DCRTH1 could play important roles in flower senescence-related signalling. Sucrose treatment did not remarkably affect the amount of DCRTE1 and DCRTH1 mRNAs.

A proteomics view on the role of drought-induced senescence and oxidative stress defense in enhanced stem reserves remobilization in wheat

Drought is one of the major factors limiting the yield of wheat (Triticum aestivum L.) particularly during grain filling. Under terminal drought condition, remobilization of pre-stored carbohydrates in wheat stem to grain has a major contribution in yield. To determine the molecular mechanism of stem reserve utilization under drought condition, we compared stem proteome patterns of two contrasting wheat landraces (N49 and N14) under a progressive post-anthesis drought stress, during which period N49 peduncle showed remarkably higher stem reserves remobilization efficiency compared to N14. Out of 830 protein spots reproducibly detected and analyzed on two-dimensional electrophoresis gels, 135 spots showed significant changes in at least one landrace. The highest number of differentially expressed proteins was observed in landrace N49 at 20days after anthesis when active remobilization of dry matter was observed, suggesting a possible involvement of these proteins in effective stem reserve remobilization of N49. The identification of 82 of differentially expressed proteins using mass spectrometry revealed a coordinated expression of proteins involved in leaf senescence, oxidative stress defense, signal transduction, metabolisms and photosynthesis which might enable N49 to efficiently remobilized its stem reserves compared to N14. The up-regulation of several senescence-associated proteins and breakdown of photosynthetic proteins in N49 might reflect the fact that N49 increased carbon remobilization from the stem to the grains by enhancing senescence. Furthermore, the up-regulation of several oxidative stress defense proteins in N49 might suggest a more effective protection against oxidative stress during senescence in order to protect stem cells from premature cell death. Our results suggest that wheat plant might response to soil drying by efficiently remobilize assimilates from stem to grain through coordinated gene expression.

Relationship between Rh-RTH1 and ethylene receptor gene expression in response to ethylene in cut rose

A cDNA clone encoding a putative RTE1-like protein (Rh-RTH1) was obtained from total RNA isolated from senescing rose (Rosa hybrida cv. Tineke) petals using RT-PCR and RACE techniques. The cDNA (1,061 bp) contained an open reading frame of 684 bp corresponding to 227 amino acids. The amino acid sequence had 60.0, 49.6, 61.2, 42.5 and 39.8% identity with that of Arabidopsis RTH, RTE1, tomato GRL2, GRL1 and GR, respectively. Northern hybridization indicated that Rh-RTH1 expression is enhanced by endogenous and exogenous ethylene and inhibited by 1-MCP in petals and gynoecia. Rh-RTH1 expression partly correlated with sites of the ethylene receptor gene Rh-ETR1 and Rh-ETR3 expression, such as the petals, gynoecia, roots, and buds. The induction of Rh-RTH1 and Rh-ETR3 expression was substantially suppressed by 1-MCP treatment, while Rh-ETR1 expression was not reduced by 1-MCP treatment. Following treatment of flowers with sucrose, the level of Rh-RTH1 and Rh-ETR3 mRNA was only slightly decreased in petals and gynoecia. Upon wounding treatment, Rh-RTH1, Rh-ETR1 and Rh-ETR3 showed a quick increase in mRNA accumulation which was positively correlated with the increase in ethylene production. The expression of Rh-RTH1 showed partial correlation with that of Rh-ETR1 and Rh-ETR3.

Sucrose prevents up-regulation of senescence-associated genes in carnation petals

cDNA microarrays were used to characterize senescence-associated gene expression in petals of cut carnation (Dianthus caryophyllus) flowers, sampled from anthesis to the first senescence symptoms. The population of PCR fragments spotted on these microarrays was enriched for flower-specific and senescence-specific genes, using subtractive hybridization. About 90% of the transcripts showed a large increase in quantity, approximately 25% transiently, and about 65% throughout the 7 d experiment. Treatment with silver thiosulphate (STS), which blocks the ethylene receptor and prevented the normal senescence symptoms, prevented the up-regulation of almost all of these genes. Sucrose treatment also considerably delayed visible senescence. Its effect on gene expression was very similar to that of STS, suggesting that soluble sugars act as a repressor of ethylene signal transduction. Two fragments that encoded a carnation EIN3-like (EIL) protein were isolated, some of which are key transcription factors that control ethylene response genes. One of these (Dc-EIL3) was up-regulated during senescence. Its up-regulation was delayed by STS and prevented by sucrose. Sucrose, therefore, seems to repress ethylene signalling, in part, by preventing up-regulation of Dc-EIL3. Some other transcription factors displayed an early increase in transcript abundance: a MYB-like DNA binding protein, a MYC protein, a MADS-box factor, and a zinc finger protein. Genes suggesting a role in senescence of hormones other than ethylene encoded an Aux/IAA protein, which regulate transcription of auxin-induced genes, and a cytokinin oxidase/dehydrogenase, which degrades cytokinin. Taken together, the results suggest a master switch during senescence, controlling the co-ordinated up-regulation of numerous ethylene response genes. Dc-EIL3 might be (part of) this master switch.

Upregulation of a tonoplast-localized cytochrome P450 during petal senescence in Petunia inflata

BACKGROUND

Gene expression in Petunia inflata petals undergoes major changes following compatible pollination. Severe flower wilting occurs reproducibly within 36 hours, providing an excellent model for investigation of petal senescence and programmed cell death. Expression of a number of genes and various enzyme activities involved in the degradation and remobilization of macromolecules have been found to be upregulated during the early stages of petal senescence.

RESULTS

By performing differential display of cDNAs during Petunia inflata petal senescence, a highly upregulated gene encoding a cytochrome P450 was identified. Analysis of the complete cDNA sequence revealed that the predicted protein is a member of the CYP74C family (CYP74C9) and is highly similar to a tomato CYP74C allene oxide synthase (AOS) that is known to be active on 9-hydroperoxides. Cloning of the petunia genomic DNA revealed an intronless gene with a promoter region that carries signals found in stress-responsive genes and potential binding sites for Myb transcription factors. Transcripts were present at detectable levels in root and stem, but were 40 times more abundant in flowers 36 hours after pollination. Ethylene and jasmonate treatment resulted in transitory increases in expression in detached flowers. A protein fusion of the CYP74C coding region to a C-terminal GFP was found to be located in the tonoplast.

CONCLUSION

Though oxylipins, particularly jasmonates, are known to be involved in stress responses, the role of other products of CYP74 enzymes is less well understood. The identification of a CYP74C family member as a highly upregulated gene during petal senescence suggests that additional products of fatty acid metabolism may play important roles during programmed cell death. In contrast to the chloroplast localization of AOS proteins in the CYP74A subfamily, GFP fusion data indicates that the petunia CYP74C9 enzyme is in the tonoplast. This result suggests that the highly similar CYP74C enzymes that have been identified in two other Solanaceous plants may also be associated with the vacuole, an organelle known to have a prominent role in programmed cell death.

Ethylene-sensitivity regulates proteolytic activity and cysteine protease gene expression in petunia corollas

To investigate ethylene's role in petal senescence, a comparative analysis of age-related changes in total protein, protease activity, and the expression of nine cysteine protease genes in the corollas of ethylene-sensitive Petuniaxhybrida cv. Mitchell Diploid (MD) and ethylene-insensitive (35S:etr1-1; line 44568) transgenic petunias was conducted. The later stages of corolla senescence in MD flowers were associated with decreased fresh weight, decreased total protein, and increased proteolytic activity. Corolla senescence was delayed by approximately 8 d in etr-44568 transgenic petunias, and decreases in corolla fresh weight, protein content, and maximum proteolytic activity were similarly delayed. Protease inhibitor studies indicated that the majority of the protease activity in senescing petals was due to cysteine proteases. Nine cysteine proteases expressed in petals were subsequently identified. Northern blot analysis indicated that six of the nine cysteine proteases showed increased transcript abundance during petal senescence. One of these cysteine proteases, PhCP10, was detected only in senescing tissues. Expression of four of the senescence-associated cysteine proteases was delayed, but not prevented in etr-44568 flowers. The other two senescence associated cysteine proteases had high levels of transcript accumulation in etr-44568 corollas at 8 d after flower opening, when MD flowers were senescing. These patterns suggest that age-related factors, other than ethylene, were regulating the up-regulation of these genes during flower ageing. The delay in visible symptoms and biochemical and molecular indicators of senescence in ethylene-insensitive flowers is consistent with the concept that ethylene modulates the timing of senescence pathways in petals.

Transcriptional regulation of three EIN3-like genes of carnation (Dianthus caryophyllus L. cv. Improved White Sim) during flower development and upon wounding, pollination, and ethylene exposure

Using a combination of approaches, three EIN3-like (EIL) genes DC-EIL1/2 (AY728191), DC-EIL3 (AY728192), and DC-EIL4 (AY728193) were isolated from carnation (Dianthus caryophyllus) petals. DC-EIL1/2 deduced amino acid sequence shares 98% identity with the previously cloned and characterized carnation DC-EIL1 (AF261654), 62% identity with DC-EIL3, and 60% identity with DC-EIL4. DC-EIL3 deduced amino acid sequence shares 100% identity with a previously cloned carnation gene fragment, Dc106 (CF259543), 61% identity with Dianthus caryophyllus DC-EIL1 (AF261654), and 59% identity with DC-EIL4. DC-EIL4 shared 60% identity with DC-EIL1 (AF261654). Expression analyses performed on vegetative and flower tissues (petals, ovaries, and styles) during growth and development and senescence (natural and ethylene-induced) indicated that the mRNA accumulation of the DC-EIL family of genes in carnation is regulated developmentally and by ethylene. DC-EIL3 mRNA showed significant accumulation upon ethylene exposure, during flower development, and upon pollination in petals and styles. Interestingly, decreasing levels of DC-EIL3 mRNA were found in wounded leaves and ovaries of senescing flowers whenever ethylene levels increased. Flowers treated with sucrose showed a 2 d delay in the accumulation of DC-EIL3 transcripts when compared with control flowers. These observations suggest an important role for DC-EIL3 during growth and development. Changes in DC-EIL1/2 and DC-EIL4 mRNA levels during flower development, and upon ethylene exposure and pollination were very similar. mRNA levels of the DC-EILs in styles of pollinated flowers showed a positive correlation with ethylene production after pollination. The cloning and characterization of the EIN3-like genes in the present study showed their transcriptional regulation not previously observed for EILs.

Similar Regulation Patterns of Choline Monooxygenase, Phosphoethanolamine N-Methyltransferase and S-Adenosyl-l-Methionine Synthetase in Leaves of the Halophyte Atriplex nummularia L

Glycinebetaine (betaine) highly accumulates as a compatible solute in certain plants and has been considered to play a role in the protection from salt stress. The betaine biosynthesis pathway of betaine-accumulating plants involves choline monooxygenase (CMO) as the key enzyme and phosphoethanolamine N-methyltransferase (PEAMT), which require S-adenosyl-L-methionine (SAM) as a methyl donor. SAM is synthesized by SAM synthetase (SAMS), and is needed not only for betaine synthesis but also for the synthesis of other compounds, especially lignin. We cloned CMO, PEAMT and SAMS isogenes from a halophyte Atriplex nummularia L. (Chenopodiaceous). The transcript and protein levels of CMO were much higher in leaves and stems than in roots, suggesting that betaine is synthesized mainly in the shoot. The regulation patterns of transcripts for SAMS and PEAMT highly resembled that of CMO in the leaves during and after relief from salt stress, and on a diurnal rhythm. In the leaves, the betaine content was increased but the lignin content was not changed by salt stress. These results suggest that the transcript levels of SAMS are co-regulated with those of PEAMT and CMO to supply SAM for betaine synthesis in the leaves.

Chalcone synthase as a reporter in virus-induced gene silencing studies of flower senescence

Agrobacterium-mediated infection of petunia (Petunia hybrida) plants with tobacco rattle virus (TRV) bearing fragments of Petunia genes resulted in systemic infection and virus-induced gene silencing (VIGS) of the homologous host genes. Infection with TRV containing a phytoene desaturase (PDS) fragment resulted in reduced abundance of PDS transcripts and typical photobleaching of photosynthetic tissues. Infection with TRV containing a chalcone synthase (CHS) fragment resulted in silencing of anthocyanin production in infected flowers. The silencing phenotype ranged from scattered white spots on the normal purple background to entirely white flowers. Symptoms in the V26 cultivar were a diffuse mosaic, but infection of some purple-flowered commercial cultivars resulted in large white sectors and even entirely white flowers. Abundance of CHS transcripts in the white flowers was less than 4% of that in purple flowers on the same plant. Infection with TRV containing a tandem construct of PDS and CHS resulted in leaf photobleaching and white patterns on the flowers. Transcripts of CHS and PDS were reduced both in leaves and in flowers confirming simultaneous silencing of both genes by the tandem construct. We tested the effects of infection with TRV containing CHS and a fragment of a petunia gene encoding for 1-aminocyclopropane-1-carboxylate oxidase (ACO4) Abundance of transcripts encoding ACO4 and ACO1 were reduced (by 5% and 20%, respectively) in infected flowers. Whether the flowers were treated with ACC or pollinated, the white (silenced) flowers or flower sectors produced less ethylene and senesced later than purple (non-silenced) tissues. These results indicate the value of VIGS with tandem constructs containing CHS as reporter and a target gene as a tool for examining the function of floral-associated genes.

Comparison of mRNA levels of three ethylene receptors in senescing flowers of carnation (Dianthus caryophyllus L.)

Three ethylene receptor genes, DC-ERS1, DC-ERS2 and DC-ETR1, were previously identified in carnation (Dianthus caryophyllus L.). Here, the presence of mRNAs for respective genes in flower tissues and their changes during flower senescence are investigated by Northern blot analysis. DC-ERS2 and DC-ETR1 mRNAs were present in considerable amounts in petals, ovaries and styles of the flower at the full-opening stage. In the petals the level of DC-ERS2 mRNA showed a decreasing trend toward the late stage of flower senescence, whereas it increased slightly in ovaries and was unchanged in styles throughout the senescence period. However, DC-ETR1 mRNA showed no or little changes in any of the tissues during senescence. Exogenously applied ethylene did not affect the levels of DC-ERS2 and DC-ETR1 mRNAs in petals. Ethylene production in the flowers was blocked by treatment with 1,1-dimethyl-4-(phenylsulphonyl)semicarbazide (DPSS), but the mRNA levels for DC-ERS2 and DC-ETR1 decreased in the petals. DC-ERS1 mRNA was not detected in any cases. These results indicate that DC-ERS2 and DC-ETR1 are ethylene receptor genes responsible for ethylene perception and that their expression is regulated in a tissue-specific manner and independently of ethylene in carnation flowers during senescence.

Is a cysteine proteinase inhibitor involved in the regulation of petal wilting in senescing carnation (Dianthus caryophyllus L.) flowers?

Senescence of carnation petals is accompanied by autocatalytic ethylene production and wilting of the petals; the former is caused by the expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase genes and the latter is related to the expression of a cysteine proteinase (CPase) gene. CPase is probably responsible for the degradation of proteins, leading to the decomposition of cell components and resultant cell death during the senescence of petals. The carnation plant also has a gene for the CPase inhibitor (DC-CPIn) that is expressed abundantly in petals at the full opening stage of flowers. In the present study, DC-CPIn cDNA was cloned and expressed in E. coli. The recombinant DC-CPIn protein completely inhibited the activities of a proteinase (CPase) extracted from carnation petals and papain. Northern blot analysis showed that the mRNA for CPase (DC-CP1) accumulated in large amounts, whereas that for DC-CPIn disappeared, corresponding to the onset of petal wilting in flowers undergoing natural senescence and exogenous ethylene-induced senescence. Based on these findings, a role of DC-CPIn in the regulation of petal wilting is suggested; DC-CPIn acts as a suppressor of petal wilting, which probably functions to fine-tune petal wilting in contrast to coarse tuning, the up-regulation of CPase activity by gene expression.

Herbivore-induced volatiles induce the emission of ethylene in neighboring lima bean plants

Herbivore attacks induce leaves to emit a specific blend of volatiles. Here we show that exposure to Tetranychus urticae-induced volatiles, as well as T. urticae infestation and artificial wounding, activates the transcription of the genes involved in the biosynthesis of ethylene [S-adenosylmethionine (SAM) synthetase and 1-aminocyclopropane-1-carboxylic acid oxidase] and a gene involved in the biosynthesis of polyamines from SAM (SAM decarboxylase) in lima bean leaves. Moreover, exposure of leaves to any one of the seven major chemical components of T. urticae-induced volatiles also induces expression of these genes. Furthermore, we found that, when lima bean plants were exposed to T. urticae-induced volatiles, they emitted ethylene. Lima bean plants infested by T. urticae and artificially wounded plants also emitted ethylene. Endogenous polyamine levels were not increased in the exposed leaves or the infested leaves, suggesting that polyamine production from SAM was only slightly promoted at the metabolic levels present in the leaves. We found that jasmonate (JA) accumulated in leaves exposed to T. urticae-induced volatiles, and that both JA and salicylate (SA) accumulated in leaves infested by T. urticae. These findings, as well as results of pharmacological analyses, suggest that, in leaves exposed to T. urticae-induced volatiles, ethylene biosynthesis might be regulated by pathways involving JA and the ethylene positive feedback loop. They also suggest that ethylene biosynthesis might be regulated by signaling pathways involving JA, SA and ethylene in T. urticae-infested leaves.

IAA and N(6)-benzyladenine inhibit ethylene-regulated expression of ACC oxidase and ACC synthase genes in mungbean hypocotyls

Regulation of expression of 1-aminocyclopropane-1-carboxylate (ACC) oxidase (VR-ACO1) and ACC synthase (VR-ACS1) genes by ethylene, indole-3-acetic acid (IAA), and N(6)-benzyladenine (BA), was investigated in mungbean hypocotyl tissues. Exogenous ethylene markedly increased transcript level of VR-ACO1 and reduced that of VR-ACS1, whereas aminooxyacetic acid (AOA), an inhibitor of ethylene biosynthesis, decreased the level of VR-ACO1 mRNA and increased that of VR-ACS1, indicating that expression of VR-ACO1 and VR-ACS1 genes are under positive and negative feedback control by ethylene, respectively. However, IAA treatment reduced the level of VR-ACO1 transcripts and increased that of VR-ACS1, although the hormone greatly induced ethylene production. We have demonstrated that, in a system that separates the effect of IAA proper from the effect of IAA-induced ethylene, the amount of IAA-induced ethylene was enough to cause accumulation of VR-ACO1 mRNA and decrease of VR-ACS1 mRNA. We have also shown that the responsiveness of VR-ACO1 and VR-ACS1 to exogenous ethylene was greatly reduced in the presence of IAA. In addition, BA abolished ethylene responsiveness with respect to expression of VR-ACO1 and VR-ACS1. Based on these results, we suggest that IAA and BA inhibit ethylene action, resulting in suppression of VR-ACO1 expression and induction of VR-ACS1 expression.

Dark-inducible genes from Arabidopsis thaliana are associated with leaf senescence and repressed by sugars

We have isolated 5 cDNA clones (din2, din6, din9, din10 and din11) corresponding to genes, the transcripts of which accumulated in leaves of Arabidopsis thaliana kept in the dark. These cDNA clones encode proteins similar to beta-glucosidase (EC 3.2.1.21, din2), asparagine synthetase (EC 6.3.5.4, din6), phosphomannose isomerase (EC 5.3.1.8, din9), seed imbibition protein (din10) and 2-oxoacid-dependent dioxygenases (din11). Accumulation of the transcripts from din6 and din10 occurred within 3 h after plants were transferred to darkness. The transcripts from din2, din9 and din11 were only detected after 24 h of dark treatment. We also observed the accumulation of the din transcripts in senescing leaves. Application of a photosynthesis inhibitor, 3-(3,4-dichlorophenyl)-1-1-dimethyl-urea, induced the expression of the din genes under illumination. Application of sucrose to detached leaves suppressed the accumulation of the din transcripts in the dark. These results indicate that expression of these genes partly depends on cellular sugar level. The sugar-modulated expression of the din genes suggests that dark-induced expression of these genes might be related to sugar starvation occurring in leaf cells in the dark, when the photosynthesis is hindered.

The ethylene pathway: a paradigm for plant hormone signaling and interaction

To dissect the web of signals that control plant growth, it is important to understand how the individual components of the pathway are modulated. Ethylene is a plant hormone involved in a large number of developmental processes. Biochemical and genetic approaches have provided a detailed view of the biosynthetic and signal transduction pathways of this hormone in the reference plant Arabidopsis thaliana. The effects of several hormones and of developmental changes on the regulation of the key enzymes of ethylene biosynthesis, ACC synthase and ACC oxidase, serve as a clear example of interaction between signals in the generation of complex responses. We now have a picture of how ethylene is sensed by the ethylene receptors and how the signal is further transduced to the nucleus. Although some of the ethylene receptors show a tissue-specific pattern of expression, little is known about the regulation of the components of the ethylene transduction cascade by other hormones or developmental factors. Once the ethylene signal reaches the nucleus, it activates a transcriptional cascade that results in changes in the expression of a number of genes. We describe some of the results that suggest an interaction at the transcriptional level between ethylene, other hormones, and stress signals.

Role of the gynoecium in natural senescence of carnation (Dianthus caryophyllus L.) flowers

Although the role of the gynoecium in natural senescence of the carnation flower has long been suggested, it has remained a matter of dispute because petal senescence in the cut carnation flower was not delayed by the removal of gynoecium. In this study, the gynoecium was snapped off by hand, in contrast to previous investigations where removal was achieved by forceps or scissors. The removal of the gynoecium by hand prevented the onset of ethylene production and prolonged the vase life of the flower, demonstrating a decisive role of the gynoecium in controlling natural senescence of the carnation flower. Abscisic acid (ABA) and indole-3-acetic acid (IAA), which induced ethylene production and accelerated petal senescence in carnation flowers, did not stimulate ethylene production in the flowers with gynoecia removed (-Gyn flowers). Application of 1-aminocyclopropane-1-carboxylate (ACC), the ethylene precursor, induced substantial ethylene production and petal wilting in the flowers with gynoecia left intact, but was less effective at stimulating ethylene production in the -Gyn flowers and negligible petal in-rolling was observed. Exogenous ethylene induced autocatalytic production of the gas and petal wilting in the -Gyn flowers. These results indicated that ethylene generated in the gynoecium triggers the onset of ethylene production in the petals of carnation during natural senescence.

Regulation of cell death in flower petals

The often rapid and synchronous programmed death of petal cells provides a model system to study molecular aspects of organ senescence. The death of petal cells is preceded by a loss of membrane permeability, due in part to increases in reactive oxygen species that are in turn related to up-regulation of oxidative enzymes and to a decrease in activity of certain protective enzymes. The senescence process also consists of a loss of proteins caused by activation of various proteinases, a loss of nucleic acids as nucleases are activated, and enzyme-mediated alterations of carbohydrate polymers. Many of the genes for these senescence-associated enzymes have been cloned. In some flowers, the degradative changes of petal cells are initiated by ethylene; in others, abscisic acid may play a role. External factors such as pollination, drought and temperature stress also affect senescence, perhaps by interacting with hormones normally produced by the flowers. Signal transduction may involve G-proteins, calcium activity changes and the regulation of protein phosphorylation and dephosphorylation. The efficacy of the floral system as well as the research tools now available make it likely that important information will soon be added to our knowledge of the molecular mechanisms involved in petal cell death.

Expression of genes responsible for ethylene production and wilting are differently regulated in carnation (Dianthus caryophyllus L.) petals

Carnation petals exhibit autocatalytic ethylene production and wilting during senescence. The autocatalytic ethylene production is caused by the expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase genes, whereas the wilting of petals is related to the expression of the cysteine proteinase (CPase) gene. So far, it has been believed that the ethylene production and wilting are regulated in concert in senescing carnation petals, since the two events occurred closely in parallel with time. In the present study, we investigated the expression of these genes in petals of a transgenic carnation harboring a sense ACC oxidase transgene and in petals of carnation flowers treated with 1,1-dimethyl-4-(phenylsulfonyl)semicarbazide (DPSS). In petals of the transgenic carnation flowers, treatment with exogenous ethylene caused accumulation of the transcript for CPase and in-rolling (wilting), whereas it caused no or little accumulation of the transcripts for ACC oxidase and ACC synthase and negligible ethylene production. In petals of the flowers treated with DPSS, the transcripts for ACC synthase and ACC oxidase were accumulated, but no significant change in the level of the transcript for CPase was observed. These results suggest that the expression of ACC synthase and ACC oxidase genes, which leads to ethylene production, is differentially regulated from the expression of CPase, which leads to wilting, in carnation petals.

Regulation of ethylene biosynthesis in response to pollination in tomato flowers

Pollination of many flowers leads to an increase in ethylene synthesis and flower senescence. We have investigated the regulation of pollination-induced ethylene synthesis in tomato (Lycopersicon esculentum) using flowers of the dialytic (dl) mutant, in which pollination can be manipulated experimentally, with the aim of developing a model system to study tomato flower senescence. Ethylene synthesis increased rapidly in dl pistils following pollination, leading to accelerated petal senescence, and was delayed in ethylene-insensitive Never-ripe (Nr) pistils. However, Nr pistils eventually produced more ethylene than dl pistils, suggesting the presence of negative feedback regulation of ethylene synthesis following pollination. LEACS1A expression correlated well with increased ethylene production in pollinated dl pistils, and expression in Nr revealed that regulation is via an ethylene-independent mechanism. In contrast, the induction of the 1-aminocyclopropane-1-carboxylic acid oxidases, LEACO1 and LEACO3, following pollination is ethylene dependent. In addition, the expression profiles of ACS and ACO genes were determined during petal senescence and a hypothesis proposed that translocated 1-aminocyclopropane-1-carboxylic acid from the pistil may be important for regulating the initial burst of ethylene production during petal senescence. These results are discussed and differences between tomato and the ornamental species previously studied are highlighted.

Isolation and characterisation of the carnation floral-specific MADS box gene, CMB2

The cDNA clone KD81, was isolated from a carnation petal cDNA library based on its strong differential expression in petals compared with leaves. The deduced amino acid sequence of KD81 indicated high homology with members of the MADS box family of transcription factors. Identified within the deduced amino acid sequence are two conserved domains; an N-terminal, MADS box and a central, K box. The gene encoding KD81 was termed Carnation MADS Box gene 2 (CMB2). Expression of CMB2 is floral-specific and in petal, transcripts were persistent from the initial stages of development through flower opening. Transcripts were not detected in vegetative tissues. The CMB2 protein is most homologous to TDR6 from tomato, the product of the petal and stamen identity gene DEFICIENS (DEFA), and several DEFA homologues including SLM3, STDEF, PMADS1 and APETALA3. Southern blot analysis indicated that CMB2 is present as a single copy within the carnation genome. Characterisation of a genomic clone encoding CMB2, revealed the molecular structure of CMB2 to be consistent with that reported for other plant MADS box genes. Analysis of the CMB2 promoter sequence revealed the presence of two putative cis-acting elements known as serum response elements (SREs). These elements are proposed as the target for MADS box domain binding and may be involved in the regulation/autoregulation of gene expression. CMB2 represents the first reported isolation of a MADS box gene from carnation.