Regulation of senescence-related gene expression in carnation flower petals by ethylene

Multi-Omics Analysis Reveals That Anthocyanin Degradation and Phytohormone Changes Regulate Red Color Fading in Rapeseed (Brassica napus L.) Petals

Flower color is an important trait for the ornamental value of colored rapeseed (Brassica napus L.), as the plant is becoming more popular. However, the color fading of red petals of rapeseed is a problem for its utilization. Unfortunately, the mechanism for the process of color fading in rapeseed is unknown. In the current study, a red flower line, Zhehuhong, was used as plant material to analyze the alterations in its morphological and physiological characteristics, including pigment and phytohormone content, 2 d before flowering (T1), at flowering (T2), and 2 d after flowering (T3). Further, metabolomics and transcriptomics analyses were also performed to reveal the molecular regulation of petal fading. The results show that epidermal cells changed from spherical and tightly arranged to totally collapsed from T1 to T3, according to both paraffin section and scanning electron microscope observation. The pH value and all pigment content except flavonoids decreased significantly during petal fading. The anthocyanin content was reduced by 60.3% at T3 compared to T1. The content of three phytohormones, 1-aminocyclopropanecarboxylic acid, melatonin, and salicylic acid, increased significantly by 2.2, 1.1, and 30.3 times, respectively, from T1 to T3. However, auxin, abscisic acid, and jasmonic acid content decreased from T1 to T3. The result of metabolomics analysis shows that the content of six detected anthocyanin components (cyanidin, peonidin, pelargonidin, delphinidin, petunidin, and malvidin) and their derivatives mainly exhibited a decreasing trend, which was in accordance with the trend of decreasing anthocyanin. Transcriptomics analysis showed downregulation of genes involved in flavonol, flavonoid, and anthocyanin biosynthesis. Furthermore, genes regulating anthocyanin biosynthesis were preferentially expressed at early stages, indicating that the degradation of anthocyanin is the main issue during color fading. The corresponding gene-encoding phytohormone biosynthesis and signaling, JASMONATE-ZIM-DOMAIN PROTEIN, was deactivated to repress anthocyanin biosynthesis, resulting in fading petal color. The results clearly suggest that anthocyanin degradation and phytohormone regulation play essential roles in petal color fading in rapeseed, which is a useful insight for the breeding of colored rapeseed.

Synthesis and characterization of bio-based quaternary ammonium salts with gibberellate or l-tryptophanate anion

Numerous biologically active acids can be transformed into an ionic form in a facile way and combined with appropriate quaternary ammonium cation to improve their application properties or biological activity. This study describes the synthesis of new quaternary ammonium salts with anions of gibberellic acid, a common plant growth regulator from the gibberellin group, or l-tryptophan, an important precursor of auxin biosynthesis. The surface-active tetrapentylammonium ion and natural substances such as acetylcholine, choline, and quinine were the sources of cations. Novel salts of gibberellic acid and l-tryptophan were obtained with high yields exceeding 97% as a result of the metathesis reaction or the neutralization of quaternary ammonium hydroxides. Phase transition temperatures, thermal and chemical stability, and solubility in solvents with different polarities were determined for all obtained salts. On the basis of studies regarding the influence of synthesized salts on the post-harvest longevity and quality of leaves of Convallaria majalis, it was established that the biological activity of the natural plant regulators in most cases was maintained. Therefore, it can be concluded that the conversion of the active substance into the form of a quaternary ammonium salt results in obtaining novel forms of plant growth regulators with favourable physicochemical properties while maintaining the efficacy of the biological active ingredients.

Graphic abstract

Enhanced Senescence Process is the Major Factor Stopping Spike Differentiation of Wheat Mutant ptsd1

Complete differentiation of the spikes guarantees the final wheat (Triticum aestivum L.) grain yield. A unique wheat mutant that prematurely terminated spike differentiation (ptsd1) was obtained from cultivar Guomai 301 treated with ethyl methane sulfonate (EMS). The molecular mechanism study on ptsd1 showed that the senescence-associated genes (SAGs) were highly expressed, and spike differentiation related homeotic genes were depressed. Cytokinin signal transduction was weakened and ethylene signal transduction was enhanced. The enhanced expression of Ca²⁺ signal transduction related genes and the accumulation of reactive oxygen species (ROS) caused the upper spikelet cell death. Many genes in the WRKY, NAC and ethylene response factor (ERF) transcription factor (TF) families were highly expressed. Senescence related metabolisms, including macromolecule degradation, nutrient recycling, as well as anthocyanin and lignin biosynthesis, were activated. A conserved tae-miR164 and a novel-miR49 and their target genes were extensively involved in the senescence related biological processes in ptsd1. Overall, the abnormal phytohormone homeostasis, enhanced Ca²⁺ signaling and activated senescence related metabolisms led to the spikelet primordia absent their typical meristem characteristics, and ultimately resulted in the phenotype of ptsd1.

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.

Intracellular energy depletion triggers programmed cell death during petal senescence in tulip

Programmed cell death (PCD) in petals provides a model system to study the molecular aspects of organ senescence. In this study, the very early triggering signal for PCD during the senescence process from young green buds to 14-d-old petals of Tulipa gesneriana was determined. The opening and closing movement of petals of intact plants increased for the first 3 d and then gradually decreased. DNA degradation and cytochrome c (Cyt c) release were clearly observed in 6-d-old flowers. Oxidative stress or ethylene production can be excluded as the early signal for petal PCD. In contrast, ATP was dramatically depleted after the first day of flower opening. Sucrose supplementation to cut flowers maintained their ATP levels and the movement ability for a longer time than in those kept in water. The onset of DNA degradation, Cyt c release, and petal senescence was also delayed by sucrose supplementation to cut flowers. These results suggest that intracellular energy depletion, rather than oxidative stress or ethylene production, may be the very early signal to trigger PCD in tulip petals.

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.

The OsEBP-89 gene of rice encodes a putative EREBP transcription factor and is temporally expressed in developing endosperm and intercalary meristem

The AP2/EREBP transcription factors play important roles in plant development and in the responses of plants to biotic and abiotic stresses. All members of the EREBP subfamily described to date are from dicotyledonous plants. In this paper, we describe the cloning and characterization of a rice gene, OsEBP-89, encoding a protein 326 amino acids long with a typical EREBP domain; this is the first report of an EREBP transcription factor in a monocotyledonous plant. Except for the EREBP domain, the OsEBP-89 protein does not have substantial sequence similarities to other members of the subfamily. The DNA-binding activity of the EREBP domain was confirmed by electrophoretic mobility-shift assays. An activation domain rich in acidic amino acids was identified by using a yeast one-hybrid system. Two putative nuclear-localization signals were also identified. The results of northern blot hybridization experiments showed that the transcript of the OsEBP-89 gene accumulates primarily in immature seeds, roots, and leaves (low levels). More detailed information about the pattern of OsEBP-89 gene expression was obtained by histochemical studies of transgenic rice plants carrying an OsEBP-89 5'/GUS reporter gene. The reporter gene was expressed in the endosperm starting at 7 days after pollination and in the intercalary meristem of plants. Expression of OsEBP-89 was induced in roots of rice seedlings by treatment with ACC, NaCl, or 2,4-D. Two cis-acting elements, an endosperm motif and a primary PERE, are present upstream of the OsEBP-89 coding region and may be involved in regulating its expression. Collectively, these results suggest that the OsEBP-89 gene is a new member of the EREBP subfamily and may be involved in ethylene-dependent seed maturation and shoot development of rice.

Negative regulation of phosphate starvation-induced genes

Phosphate (Pi) deficiency is a major nutritional problem faced by plants in many agro-ecosystems. This deficiency results in altered gene expression leading to physiological and morphological changes in plants. Altered gene expression is presumed to be due to interaction of regulatory sequences (cis-elements) present in the promoters with DNA binding factors (trans-factors). In this study, we analyzed the expression and DNA-protein interaction of promoter regions of Pi starvation-induced genes AtPT2 and TPSI1. AtPT2 encodes the high-affinity Pi transporter in Arabidopsis, whereas TPSI1 codes for a novel gene induced in the Pi-starved tomato (Lycopersicon esculentum). Expression of AtPT2 was induced rapidly under Pi deficiency and increased with decreasing concentrations of Pi. Abiotic stresses except Pi starvation had no affect on the expression of TPSI1. DNA mobility-shift assays indicated that specific sequences of AtPT2 and TPSI1 promoter interact with nuclear protein factors. Two regions of AtPT2 and TPSI1 promoters specifically bound nuclear protein factors from Pi-sufficient plants. Interestingly, the DNA binding activity disappeared during Pi starvation, leading to the hypothesis that Pi starvation-induced genes may be under negative regulation.

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.

Programmed cell death during pollination-induced petal senescence in petunia

Petal senescence, one type of programmed cell death (PCD) in plants, is a genetically controlled sequence of events comprising its final developmental stage. We characterized the pollination-induced petal senescence process in Petunia inflata using a number of cell performance markers, including fresh/dry weight, protein amount, RNA amount, RNase activity, and cellular membrane leakage. Membrane disruption and DNA fragmentation with preferential oligonucleosomal cleavage, events characteristic of PCD, were found to be present in the advanced stage of petal senescence, indicating that plant and animal cell death phenomena share one of the molecular events in the execution phase. As in apoptosis in animals, both single-stranded DNase and double-stranded DNase activities are induced during petal cell death and are enhanced by Ca(2+). In contrast, the release of cytochrome c from mitochondria, one commitment step in signaling of apoptosis in animal cells, was found to be dispensable in petal cell death. Some components of the signal transduction pathway for PCD in plants are likely to differ from those in animal cells.

Differential expression of three members of the 1-aminocyclopropane-1-carboxylate synthase gene family in carnation

We investigated the expression patterns of three 1-aminocyclopropane-1-carboxylate (ACC) synthase genes in carnation (Dianthus caryophyllus cv White Sim) under conditions previously shown to induce ethylene biosynthesis. These included treatment of flowers with 2,4-dichlorophenoxyacetic acid, ethylene, LiCl, cycloheximide, and natural and pollination-induced flower senescence. Accumulation of ACC synthase transcripts in leaves following mechanical wounding and treatment with 2,4-dichlorophenoxyacetic acid or LiCl was also determined by RNA gel-blot analysis. As in other species, the carnation ACC synthase genes were found to be differentially regulated in a tissue-specific manner. DCACS2 and DCACS3 were preferentially expressed in styles, whereas DCACS1 mRNA was most abundant in petals. Cycloheximide did not induce increased accumulation of ACC synthase transcripts in carnation flowers, whereas the expression of ACC synthase was up-regulated by auxin, ethylene, LiCl, pollination, and senescence in a floral-organ-specific manner. Expression of the three ACC synthases identified in carnation did not correspond to elevated ethylene biosynthesis from wounded or auxin-treated leaves, and there are likely additional members of the carnation ACC synthase gene family responsible for ACC synthase expression in vegetative tissues.

Pollination-Induced Ethylene in Carnation (Role of Stylar Ethylene in Corolla Senescence)

In carnation (Dianthus caryophyllus L. cv White Sim) cell to cell communication between the pollen and pistil induces ovary development and corolla senescence. The production of elevated ethylene by the style is the first measurable postpollination response. This is followed by a wave of ethylene production from the other floral organs. To investigate the regulation of ethylene biosynthesis in pollinated flowers we measured ethylene production and the expression of 1-aminocyclopropane-1-carboxylate synthase and 1-aminocyclopropane-1-carboxylate oxidase transcripts in individual floral organs after pollination. Ethylene production by pollinated styles can be defined temporally by three distinct peaks. By pollinating a single style from a multistyle gynoecium, it was determined that the unpollinated style produces ethylene that corresponds to the first and third peaks observed from a pollinated style. Inhibition of ethylene action in the pollinated style by diazocyclopentadiene treatment prevented both pollination-induced corolla senescence and ethylene production from the ovaries and petals. Treatment with diazocyclopentadiene decreased stylar ethylene production during the second peak and completely inhibited the third peak of ethylene in both pollinated and unpollinated styles. This later auto-catalytic ethylene in styles is likely responsible for pollination-induced corolla senescence and ovary development.

POLLINATION REGULATION OF FLOWER DEVELOPMENT

▪ Abstract  Pollination regulates a syndrome of developmental responses that contributes to successful sexual reproduction in higher plants. Pollination-regulated developmental events collectively prepare the flower for fertilization and embryogenesis while bringing about the loss of floral organs that have completed their function in pollen dispersal and reception. Components of this process include changes in flower pigmentation, senescence and abscission of floral organs, growth and development of the ovary, and, in certain cases, pollination also triggers ovule and female gametophyte development in anticipation of fertilization. Pollination-regulated development is initiated by the primary pollination event at the stigma surface, but because developmental processes occur in distal floral organs, the activity of interorgan signals that amplify and transmit the primary pollination signal to floral organs is implicated. Interorgan signaling and signal amplification involves the regulation of ethylene biosynthetic gene expression and interorgan transport of hormones and their precursors. The coordination of pollination- regulated flower development including gametophyte, embryo, and ovary development; pollination signaling; the molecular regulation of ethylene biosynthesis; and interorgan communication are presented.

Ethylene-regulated expression of a carnation cysteine proteinase during flower petal senescence

The senescence of carnation (Dianthus caryophyllus L.) flower petals is regulated by the phytohormone ethylene and is associated with considerable catabolic activity including the loss of protein. In this paper we present the molecular cloning of a cysteine proteinase and show that its expression is regulated by ethylene and associated with petal senescence. A 1600 bp cDNA was amplified by polymerase chain reaction using a 5'-specific primer and 3'-nonspecific primer designed to amplify a 1-aminocyclopropane-1-carboxylate synthase cDNA from reverse-transcribed stylar RNA. The nucleotide sequence of the cloned product (pDCCP1) was found to share significant homology to several cysteine proteinases rather than ACC synthase. A single open reading frame of 428 amino acids was shown to share significant homology with other plant cysteine proteinases including greater than 70% identity with a cysteine proteinase from Arabidopsis thaliana. Amino acids in the active site of cysteine proteinases were conserved in the pDCCP1 peptide. RNA gel blot analysis revealed that the expression of pDCCP1 increased substantially with the onset of ethylene production and senescence of petals. Increased pDCCP1 expression was also associated with ethylene production in other senescing floral organs including ovaries and styles. The pDCCP1 transcript accumulated in petals treated with exogenous ethylene within 3 h and treatment of flowers with 2,5-norbornadiene, an inhibitor of ethylene action, prevented the increase in pDCCP1 expression in petals. The temporal and spatial patterns of pDCCP1 expression suggests a role for cysteine proteinase in the loss of protein during floral senescence.

Molecular cloning of two different ACC synthase PCR fragments in carnation flowers and organ-specific expression of the corresponding genes

Degenerate oligonucleotides to highly conserved regions of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.4.1.14), the key enzyme in ethylene biosynthesis, were used to prime the synthesis and amplification of fragments of about 1,180 bp by polymerase chain reaction (PCR) in samples of cDNA to total RNA isolated from senescing carnation (Dianthus caryophyllus) flowers. Two putative ACC synthase PCR clones were isolated one of which was identical to the sequence of a carnation ACC synthase cDNA clone (CARACC3) recently isolated by Park et al. (Plant Mol Biol 18 (1992) 377-386). The other clone (CARAS1) was ca. 66% homologous at the amino acid level to CARACC3. For both ACC synthase clones, specific oligonucleotides were synthesized and, using PCR, we were able to distinguish between the two ACC synthase transcripts in samples of total RNA isolated from different carnation flower parts and leaves. DNA blots of PCR fragments revealed that, in flowers, both ageing and ethylene stimulated the occurrence of these transcripts in an organ-specific way. CARACC3 was more abundant in RNA from the petals whereas CARAS1 was more abundant in RNA from the styles. Despite a high ethylene production observed in ovaries, the level of both transcripts was low, suggesting the existence of a third ACC synthase gene that is specifically expressed in the ovary. Transcript levels in leaves were low irrespective of treatment.

An ethylene-responsive enhancer element is involved in the senescence-related expression of the carnation glutathione-S-transferase (GST1) gene

The increased production of ethylene during carnation petal senescence regulates the transcription of the GST1 gene encoding a subunit of glutathione-S-transferase. We have investigated the molecular basis for this ethylene-responsive transcription by examining the cis elements and trans-acting factors involved in the expression of the GST1 gene. Transient expression assays following delivery of GST1 5' flanking DNA fused to a beta-glucuronidase receptor gene were used to functionally define sequences responsible for ethylene-responsive expression. Deletion analysis of the 5' flanking sequences of GST1 identified a single positive regulatory element of 197 bp between -667 and -470 necessary for ethylene-responsive expression. The sequences within this ethylene-responsive region were further localized to 126 bp between -596 and -470. The ethylene-responsive element (ERE) within this region conferred ethylene-regulated expression upon a minimal cauliflower mosaic virus-35S TATA-box promoter in an orientation-independent manner. Gel electrophoresis mobility-shift assays and DNase I footprinting were used to identify proteins that bind to sequences within the ERE. Nuclear proteins from carnation petals were shown to specifically interact with the 126-bp ERE and the presence and binding of these proteins were independent of ethylene or petal senescence. DNase I footprinting defined DNA sequences between -510 and -488 within the ERE specifically protected by bound protein. An 8-bp sequence (ATTTCAAA) within the protected region shares significant homology with promoter sequences required for ethylene responsiveness from the tomato fruit-ripening E4 gene.

Pistil-Specific and Ethylene-Regulated Expression of 1-Aminocyclopropane-1-Carboxylate Oxidase Genes in Petunia Flowers

The differential expression of the petunia 1-aminocyclopropane-1-carboxylate (ACC) oxidase gene family during flower development and senescence was investigated. ACC oxidase catalyzes the conversion of ACC to ethylene. The increase in ethylene production by petunia corollas during senescence was preceded by increased ACC oxidase mRNA and enzyme activity. Treatment of flowers with ethylene led to an increase in ethylene production, ACC oxidase mRNA, and ACC oxidase activity in corollas. In contrast, leaves did not exhibit increased ethylene production or ACC oxidase expression in response to ethylene. Gene-specific probes revealed that the ACO1 gene was expressed specifically in senescing corollas and in other floral organs following exposure to ethylene. The ACO3 and ACO4 genes were specifically expressed in developing pistil tissue. In situ hybridization experiments revealed that ACC oxidase mRNAs were specifically localized to the secretory cells of the stigma and the connective tissue of the receptacle, including the nectaries. Treatment of flower buds with ethylene led to patterns of ACC oxidase gene expression spatially distinct from the patterns observed during development. The timing and tissue specificity of ACC oxidase expression during pistil development were paralleled by physiological processes associated with reproduction, including nectar secretion, accumulation of stigmatic exudate, and development of the self-incompatible response.

Analysis of an osmotically regulated pathogenesis-related osmotin gene promoter

Osmotin is a small (24 kDa), basic, pathogenesis-related protein, that accumulates during adaptation of tobacco (Nicotiana tabacum) cells to osmotic stress. There are more than 10 inducers that activate the osmotin gene in various plant tissues. The osmotin promoter contains several sequences bearing a high degree of similarity to ABRE, as-1 and E-8 cis element sequences. Gel retardation studies indicated the presence of at least two regions in the osmotin promoter that show specific interactions with nuclear factors isolated from cultured cells or leaves. The abundance of these binding factors increased in response to salt, ABA and ethylene. Nuclear factors protected a 35 bp sequence of the promoter from DNase I digestion. Different 5' deletions of the osmotin promoter cloned into a promoter-less GUSNOS plasmid (pBI 201) were used in transient expression studies with a Biolistic gun. The transient expression studies revealed the presence of three distinct regions in the osmotin promoter. The promoter sequence from -108 to -248 bp is absolutely required for reporter gene activity, followed by a long stretch (up to -1052) of enhancer-like sequence and then a sequence upstream of -1052, which appears to contain negative elements. The responses to ABA, ethylene, salt, desiccation and wounding appear to be associated with the -248 bp sequence of the promoter. This region also contains a putative ABRE (CACTGTG) core element. Activation of the osmotin gene by various inducers is discussed in view of antifungal activity of the osmotin protein.

Temporal and spatial regulation of 1-aminocyclopropane-1-carboxylate oxidase in the pollination-induced senescence of orchid flowers

Pollination of many flowers initiates a sequence of precisely regulated developmental events that include senescence of the perianth and development of the ovary. The plant hormone ethylene is known to play a key role in regulating the biochemical and anatomical changes that constitute the postpollination syndrome. For this reason, we have studied the pollination syndrome in Phalaenopsis orchids by examining the spatial and temporal location of ethylene biosynthesis within the orchid flower, and how this biosynthesis is regulated by factors that influence expression of genes that encode key enzymes in the ethylene biosynthetic pathway. In particular, we examined the role in the postpollination syndrome of the expression of the gene for 1-aminocyclopropane-1-carboxylate (ACC) oxidase, which catalyzes the conversion of ACC to ethylene. In vivo incubation of tissues with the ethylene precursor ACC demonstrated that ACC oxidase activity increases after pollination in the stigma, contrary to the observation that activity is constitutive in petunia and carnation gynoecia. RNA blot hybridization of floral tissues indicates that the increase in ACC oxidase activity is due to de novo synthesis of mRNA and presumably protein, which is induced after pollination. Furthermore, the pattern of induction is consistent with a model of coordinate regulation of gene expression in which the pollination signal travels to other organs of the flower to induce their ethylene production. We have also used in situ hybridization to define further the temporal and spatial expression of ACC oxidase within the floral organs, showing that expression, and,by inference, the capability to oxidize ACC to ethylene, is induced in all living cells of the tissues examined after pollination. These findings contrast with work in petunia that suggests that ACC oxidase is localized to the stigmatic surface.

The Arabidopsis 1-Aminocyclopropane-1-Carboxylate Synthase Gene 1 Is Expressed during Early Development

The temporal and spatial expression of one member of the Arabidopsis 1-aminocyclopropane-1-carboxylate (ACC) synthase gene family (ACS1) was analyzed using a promoter-[beta]-glucuronidase fusion. The expression of ACS1 is under developmental control both in shoot and root. High expression was observed in young tissues and was switched off in mature tissues. ACS1 promoter activity was strongly correlated with lateral root formation. Dark-grown seedlings exhibited a different expression pattern from light-grown ones. The ACC content and the in vivo activity of ACC oxidase were determined. ACC content correlated with ACS1 gene activity. ACC oxidase activity was demonstrated in young Arabidopsis seedlings. Thus, the ACC formed can be converted into ethylene. In addition, ethylene production of immature leaves was fourfold higher compared to that of mature leaves. The possible involvement of ACS1 in influencing plant growth and development is discussed.

A flower senescence-related mRNA from carnation encodes a novel protein related to enzymes involved in phosphonate biosynthesis

We have isolated a cDNA clone (pSR132) representing a mRNA which accumulates in senescing carnation flower petals in response to ethylene. In vitro translation of RNA selected by hybridization with pSR132 indicated the mRNA encoded a polypeptide of approximately 36 kDa. This was confirmed by DNA sequence analysis, which predicted a peptide composed of 318 amino acids with a calculated molecular weight of 34.1 kDa. Comparison of the predicted peptide sequence of pSR132 with other proteins compiled in the NBRF data base revealed significant homology with carboxyphosphonoenolpyruvate mutase and phosphoenolpyruvate mutase from Streptomyces hygroscopicus and Tetrahymena pyriformis, respectively. These enzymes are involved in the formation of C-P bonds in the biosynthesis of phosphonates. C-P bonds are found in a wide range of organisms, but their presence or formation in higher plants has not been investigated.

An Arabidopsis gene with homology to glutathione S-transferases is regulated by ethylene

A cDNA clone obtained from Arabidopsis leaf RNA encodes a 24 kDa protein with homology to glutathione S-transferases (GST). It is most homologous with a tobacco GST (57% identity). In Arabidopsis, expression of GST mRNA is regulated by ethylene. Exposure of plants to ethylene increased the abundance of GST mRNA, while treatment with norbornadiene had the reverse effect. Ethylene had no effect on the mRNA level in ethylene-insensitive etr1 plants. The abundance of this mRNA increased with the age of plants. DNA hybridizations indicate that GSTs are encoded by a large multigene family in Arabidopsis.

Characterization of an ethylene-responsive glutathione S-transferase gene cluster in carnation

In this paper we present the structural analysis of two tightly linked genes from the glutathione S-transferase (GST) gene family in carnation (Dianthus caryophyllus). Southern blot analysis and restriction endonuclease mapping revealed a single cloned region of the carnation genome was highly homologous to the previously characterized ethylene-responsive GST mRNA expressed in flower petals during senescence. Nucleotide sequencing of this region revealed the presence of two tandemly arranged genes designated GST1 and GST2. Comparison of the nucleotide sequences of the cloned genomic region with the previously characterized GST cDNA clone pSR8 revealed that GST1 contains the entire transcription unit in 10 exons interrupted by 9 introns. The transcription unit of GST2 was found to be very similar to GST1 with complete conservation of intron position. In addition, the length and nucleotide sequences of the two genes' introns were highly conserved. GST2 was not completely represented by the cloned genomic region, missing the 3' portion of the transcription unit. Primer extension analysis indicated a single transcriptional start site for transcripts which accumulate in senescing carnation petals. The 5'-flanking sequences of GST1 and GST2 were compared and regions of homology and divergence identified. These upstream sequences were compared with other plant ethylene-responsive genes and GST genes and several sequence motifs of potential importance in the regulation of GST expression were identified. A chimeric gene constructed between -1457 bp of the 5'-flanking DNA of GST1 and the coding region of beta-glucuronidase was found to confer ethylene-inducible expression in flower petals following delivery of the construct into tissue by particle bombardment.

Identification, cDNA Cloning, and Analysis of mRNAs Having Altered Expression in Tips of Harvested Asparagus Spears

Changes in mRNA activity in tips of harvested asparagus spears (Asparagus officinalis L.) held in light or dark for up to 48 h at 20 degrees C were investigated as an initial step in elucidating the genetic response of asparagus spears to harvest. Total RNA was isolated from 30-mm tips of spears 180 mm in length at 0, 6, 12, 24, and 48 h after spear harvest and translated in vitro, and translation products were separated using both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional polyacrylamide gel electrophoresis. We detected 25 consistent changes in translatable mRNAs, involving both increase and decrease in mRNA abundance. The majority of the changes occurred within 12 h of harvest. Most of the changes were not light regulated. cDNA libraries were constructed from polyadenylated mRNA extracted from tips of spears at harvest (0 h) and after 12 h in the dark at 20 degrees C. Differential hybridization screening of the cDNA libraries isolated nine cDNA clones whose corresponding transcripts had altered expression after harvest. Investigations of mRNA activity during spear development demonstrated that the changes detected were harvest related. Possible roles for the mRNAs corresponding to the isolated clones in tips of harvested spears are discussed.

Expression of ethylene biosynthetic pathway transcripts in senescing carnation flowers

We have examined the expression of mRNAs for S-adenosylmethionine synthetase (EC 2.5.1.6), 1-aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14), and the ethylene-forming enzyme (EFE) in various floral organs of carnation (Dianthus caryophyllus) during the increase in ethylene biosynthesis associated with petal senescence. The abundance of ACC synthase and EFE mRNAs increased and S-adenosylmethionine synthetase transcripts decreased concomitantly with the ethylene climacteric in senescing petals. The increase in abundance of ACC synthase and EFE mRNAs in aging flowers was prevented by treatment with the ethylene action inhibitor 2,5-norbornadiene. Furthermore, an increase in ACC synthase and EFE transcripts was detected in petals from presenescent flowers within 3 to 6 hours of exposure to 2 microliters per liter of ethylene. The increase in ethylene production by senescing petals was associated with a concomitant increase in ethylene biosynthesis in styles, ovary, and receptacle tissues. In all tissues, this increase was associated with increased activities of ACC synthase and EFE. The increase in EFE activities by all floral organs examined was correlated with increased abundance of EFE transcripts. In contrast, the level of ACC synthase mRNA, as detected by the cDNA probe pCARACC3, did not always reflect enzyme activity. The combined tissues of the pistil exhibited high rates of ACC synthase activity but contained low levels of ACC synthase mRNAs homologous to pCARACC3. In addition, pollinated styles exhibited a rapid increase in ethylene production and ACC synthase activity but did not accumulate detectable levels of ACC synthase mRNA until several hours after the initiation of ethylene production. These results suggest that transcripts for ACC synthase leading to the early postpollination increase in ACC synthase activity and ethylene production are substantially different from the mRNA for the ethylene-responsive gene represented by pCARACC3.

Ethylene Synthesis and Floral Senescence following Compatible and Incompatible Pollinations in Petunia inflata

Ethylene production and floral senescence following compatible and incompatible pollinations were studied in a self-incompatible species, Petunia inflata. Both compatible and incompatible pollinations resulted in a burst of ethylene synthesis that peaked 3 hours after pollination. P. inflata pollen was found to carry large amounts of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). The amount of pollen-held ACC varied in different genetic backgrounds, and the magnitude of the peak correlated with the amount of ACC borne by the pollen. Aminooxyacetic acid (AOA), an inhibitor of ACC synthesis, had no inhibitory effect on this ethylene response, indicating that pollen-borne ACC was largely responsible for the early synthesis of ethylene. After compatible pollination, a second increase in ethylene synthesis began at 18 hours, and the first sign of senescence appeared at 36 hours. Upon treatment with AOA, the second phase of ethylene production was reduced by 95%, indicating that endogenous ACC synthesis was required for this phase of ethylene synthesis. AOA treatment also delayed senescence to 6 days after anthesis. After incompatible pollination, a second increase in ethylene production did not occur until 3 days, and the first sign of senescence occurred 12 hours later. Unpollinated flowers showed an increase in ethylene production 3 to 4 days after anthesis and displayed signs of senescence 1 day later. The significance of the early and late phases of pollination-induced ethylene synthesis is discussed.

Enhanced Sensitivity to Ethylene in Nitrogen- or Phosphate-Starved Roots of Zea mays L. during Aerenchyma Formation

Adventitious roots of maize (Zea mays L. cv TX 5855), grown in a well-oxygenated nutrient solution, were induced to form cortical gas spaces (aerenchyma) by temporarily omitting nitrate and ammonium (-N), or phosphate (-P), from the solution. Previously this response was shown (MC Drew, CJ He, PW Morgan [1989] Plant Physiology 91: 266-271) to be associated with a slower rate of ethylene biosynthesis, contrasting with the induction of aerenchyma by hypoxia during which ethylene production is strongly stimulated. In the present paper, we show that aerenchyma formation induced by nutrient starvation was blocked, under noninjurious conditions, by addition of low concentrations of Ag(+), an inhibitor of ethylene action, or of aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. When extending roots were exposed to low concentrations of ethylene in air sparged through the nutrient solution, N or P starvation enhanced the sensitivity to exogenous ethylene at concentrations as low as 0.05 microliters ethylene per liter air, promoting a more rapid and extensive formation of aerenchyma than in unstarved roots. We conclude that temporary deprivation of N or P enhances the sensitivity of ethylene-responsive cells of the root cortex, leading to cell lysis and aerenchyma.

An ethylene-responsive flower senescence-related gene from carnation encodes a protein homologous to glutathione S-transferases

Carnation flower petal senescence is associated with the expression of specific senescence-related mRNAs, several of which were previously cloned. The cDNA clone pSR8 represents a transcript which accumulates specifically in senescing flower petals in response to ethylene. Here we report the structural characterization of this cDNA. A second cDNA clone was isolated based on shared sequence homology with pSR8. This clone, pSR8.4, exhibited an overlapping restriction endonuclease map with pSR8 and contained an additional 300 nucleotides. Primer extension analysis revealed the combined cDNAs to be near full-length and the transcript to accumulate in senescing petals. Analysis of the nucleotide sequence of SR8 cDNAs revealed an open reading frame of 220 amino acids sufficient to encode a 25 kDa polypeptide. Comparison of the deduced polypeptide sequence of pSR8 with other peptide sequences revealed significant similarity with glutathione s-transferases from a variety of organisms. The predicted polypeptide sequence shared 44%, 53% and 52% homology with GSTs from maize, Drosophila and man, respectively. We discuss our results in relation to the biochemistry of flower petal senescence and the possible role of glutathione s-transferase in this developmental process.

Characterization of an ethylene-regulated flower senescence-related gene from carnation

The programmed senescence of carnation (Dianthus caryophyllus L.) petals requires active gene expression and is associated with the expression of several senescence-related mRNAs. Expression of the mRNA represented by the cDNA clone pSR12 has previously been shown to be transcriptionally activated by ethylene specifically in senescing flowers. We report in this paper the structural analysis of this cDNA and its corresponding gene. One cloned genomic DNA fragment, SR12-B, contained the entire transcription unit in 17 exons, interrupted by 16 introns. A second gene, SR12-A, was highly homologous to SR12-B with several nucleotide substitutions and a 489 bp deletion in the 5' flanking DNA sequence. The SR12 transcript has an open reading frame of 2193 bp sufficient to encode a protein of 82.8 kDa. No significant homology at the DNA or protein levels was found with other known genes. We have identified a DNA-binding factor which specifically interacts with two upstream fragments (-149 to -337 and -688 to -1055) of SR12-B. Both fragments apparently compete for the same binding factor. The DNA-binding activity was present in nuclear extracts from both presenescent and senescing carnation petals. The upstream DNA fragments that bind this factor have sequence homology with promoter sequences of other ethylene-regulated genes.