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

Aging later but faster: how StCDF1 regulates senescence in Solanum tuberosum

In potato, maturity is assessed by leaf senescence, which, in turn, affects yield and tuber quality traits. Previously, we showed that the CYCLING DOF FACTOR1 (StCDF1) locus controls leaf maturity in addition to the timing of tuberization. Here, we provide evidence that StCDF1 controls senescence onset separately from senescence progression and the total life cycle duration. We used molecular-biological approaches (DNA-Affinity Purification Sequencing) to identify a direct downstream target of StCDF1, named ORESARA1 (StORE1S02), which is a NAC transcription factor acting as a positive senescence regulator. By overexpressing StORE1S02 in the long life cycle genotype, early onset of senescence was shown, but the total life cycle remained long. At the same time, StORE1S02 knockdown lines have a delayed senescence onset. Furthermore, we show that StORE1 proteins play an indirect role in sugar transport from source to sink by regulating expression of SWEET sugar efflux transporters during leaf senescence. This study clarifies the important link between tuber formation and senescence and provides insight into the molecular regulatory network of potato leaf senescence onset. We propose a complex role of StCDF1 in the regulation of potato plant senescence.

Signalling cascades choreographing petal cell death: implications for postharvest quality

Senescence is a multifaceted and dynamic developmental phase pivotal in the plant's lifecycle, exerting significant influence and involving intricate regulatory mechanisms marked by a variety of structural, biochemical and molecular alterations. Biochemical changes, including reactive oxygen species (ROS) generation, membrane deterioration, nucleic acid degradation and protein degradation, characterize flower senescence. The progression of senescence entails a meticulously orchestrated network of interconnected molecular mechanisms and signalling pathways, ensuring its synchronized and efficient execution. Within flowering plants, petal senescence emerges as a crucial aspect significantly impacting flower longevity and postharvest quality, emphasizing the pressing necessity of unravelling the underlying signalling cascades orchestrating this process. Understanding the complex signalling pathways regulating petal senescence holds paramount importance, not only shedding light on the broader phenomenon of plant senescence but also paving the way for the development of targeted strategies to enhance the postharvest longevity of cut flowers. Various signalling pathways participate in petal senescence, encompassing hormone signalling, calcium signalling, protein kinase signalling and ROS signalling. Among these, the ethylene signalling pathway is extensively studied, and the manipulation of genes associated with ethylene biosynthesis or signal transduction has demonstrated the potential to enhance flower longevity. A thorough understanding of these complex pathways is critical for effectively delaying flower senescence, thereby enhancing postharvest quality and ornamental value. Therefore, this review adopts a viewpoint that combines fundamental research into the molecular intricacies of senescence with a practical orientation towards developing strategies for improving the postharvest quality of cut flowers. The innovation of this review is to shed light on the pivotal signalling cascades underpinning flower senescence and offer insights into potential approaches for modulating these pathways to postpone petal senescence in ornamental plants.

Tulip transcription factor TgWRKY75 activates salicylic acid and abscisic acid biosynthesis to synergistically promote petal senescence

WRKY transcription factors play a central role in controlling plant organ senescence; however, it is unclear whether and how they regulate petal senescence in the widely grown ornamental plant tulip (Tulipa gesneriana). In this study, we report that TgWRKY75 promotes petal senescence by enhancing the synthesis of both abscisic acid (ABA) and salicylic acid (SA) in tulip and in transgenic Arabidopsis. The expression level of TgWRKY75 was up-regulated in senescent petals, and exogenous ABA or SA treatment induced its expression. The endogenous contents of ABA and SA significantly increased during petal senescence and in response to TgWRKY75 overexpression. Two SA synthesis-related genes, TgICS1 and TgPAL1, were identified as direct targets of TgWRKY75, which binds to their promoters. In parallel, TgWRKY75 activated the expression of the ABA biosynthesis-related gene TgNCED3 via directly binding to its promoter region. Site mutation of the W-box core motif located in the promoters of TgICS1, TgPAL1, and TgNCED3 eliminated their interactions with TgWRKY75. In summary, our study demonstrates a dual regulation of ABA and SA biosynthesis by TgWRKY75, revealing a synergistic process of tulip petal senescence through feedback regulation between TgWRKY75 and the accumulation of ABA and SA.

An efficient screening system of disease-resistant genes from wild apple, Malus sieversii in response to Valsa mali pathogenic fungus

For molecular breeding of future apples, wild apple (Malus sieversii), the primary progenitor of domesticated apples, provides abundant genetic diversity and disease-resistance traits. Valsa canker (caused by the fungal pathogen Valsa mali) poses a major threat to wild apple population as well as to cultivated apple production in China. In the present study, we developed an efficient system for screening disease-resistant genes of M. sieversii in response to V. mali. An optimal agrobacterium-mediated transient transformation of M. sieversii was first used to manipulate in situ the expression of candidate genes. After that, the pathogen V. mali was inoculated on transformed leaves and stems, and 3 additional methods for slower disease courses were developed for V. mali inoculation. To identify the resistant genes, a series of experiments were performed including morphological (incidence, lesion area/length, fungal biomass), physiological (H2O2 content, malondialdehyde content), and molecular (Real-time quantitative Polymerase Chain Reaction) approaches. Using the optimized system, we identified two transcription factors with high resistance to V. mali, MsbHLH41 and MsEIL3. Furthermore, 35 and 45 downstream genes of MsbHLH41 and MsEIL3 were identified by screening the V. mali response gene database in M. sieversii, respectively. Overall, these results indicate that the disease-resistant gene screening system has a wide range of applications for identifying resistant genes and exploring their immune regulatory networks.

Senescence in dahlia flowers is regulated by a complex interplay between flower age and floret position

Mechanisms regulating flower senescence are not fully understood in any species and are particularly complex in composite flowers. Dahlia (Dahlia pinnata Cav.) florets develop sequentially, hence each composite flower head includes florets of different developmental stages as the whole flower head ages. Moreover, the wide range of available cultivars enables assessment of intraspecific variation. Transcriptomes were compared amongst inner (younger) and outer (older) florets of two flower head ages to assess the effect of floret vs. flower head ageing. More gene expression, including ethylene and cytokinin pathway expression changed between inner and outer florets of older flower heads than between inner florets of younger and older flower heads. Additionally, based on Arabidopsis network analysis, different patterns of co-expressed ethylene response genes were elicited. This suggests that changes occur in young inner florets as the whole flower head ages that are different to ageing florets within a flower head. In some species floral senescence is orchestrated by the plant growth regulator ethylene. However, there is both inter and intra-species variation in its importance. There is a lack of conclusive data regarding ethylene sensitivity in dahlia. Speed of senescence progression, effects of ethylene signalling perturbation, and patterns of ethylene biosynthesis gene expression differed across three dahlia cultivars ('Sylvia', 'Karma Prospero' and 'Onesta') suggesting differences in the role of ethylene in their floral senescence, while effects of exogenous cytokinin were less cultivar-specific.

Protein Kinase RhCIPK6 Promotes Petal Senescence in Response to Ethylene in Rose (Rosa Hybrida)

Cultivated roses have the largest global market share among ornamental crops. Postharvest release of ethylene is the main cause of accelerated senescence and decline in rose flower quality. To understand the molecular mechanism of ethylene-induced rose petal senescence, we analyzed the transcriptome of rose petals during natural senescence as well as with ethylene treatment. A large number of differentially expressed genes (DEGs) were observed between developmental senescence and the ethylene-induced process. We identified 1207 upregulated genes in the ethylene-induced senescence process, including 82 transcription factors and 48 protein kinases. Gene Ontology enrichment analysis showed that ethylene-induced senescence was closely related to stress, dehydration, and redox reactions. We identified a calcineurin B-like protein (CBL) interacting protein kinase (CIPK) family gene in Rosa hybrida, RhCIPK6, that was regulated by age and ethylene induction. Reducing RhCIPK6 expression through virus-induced gene silencing significantly delayed petal senescence, indicating that RhCIPK6 mediates petal senescence. In the RhCIPK6-silenced petals, several senescence associated genes (SAGs) and transcription factor genes were downregulated compared with controls. We also determined that RhCIPK6 directly binds calcineurin B-like protein 3 (RhCBL3). Our work thus offers new insights into the function of CIPKs in petal senescence and provides a genetic resource for extending rose vase life.

Differential expression of ethylene biosynthetic and receptor genes in pollination-induced senescence of Dendrobium flowers

Following successful pollination, Dendrobium orchid flowers rapidly undergo senescence. In Dendrobium cv. Khao Chaimongkol, compatible pollination resulted in faster ethylene production and more rapid development of senescence symptoms, such as drooping, epinasty, venation and yellowing, compared with non-pollinated controls or pollination with incompatible pollinia. The DenACS1 and DenACO1 genes in the perianth of florets that had been pollinated with compatible pollinia were expressed more highly than those in non-pollinated open florets. Incompatible pollinia reduced the expression of DenACS1 and DenACO1 genes in the perianth. Transcript levels of the ethylene receptor gene DenERS1 and signaling genes DenEIL1 and DenERF1 showed differential spatial regulation with greater expression in the perianth than in the column plus ovary following compatible pollination. Compatible pollinia increased ethylene production concomitant with premature senescence and the increased expression of the DenACS1 and DenACO1 genes, and suppressed the ethylene receptor gene DenERS1, whereas incompatible pollinia did not stimulate ethylene production nor induce premature senescence but induced higher expression of DenERS1 both in the perianth and in the column plus ovary. These results suggest that the increased ethylene production in open florets pollinated with compatible pollen was partially due to an increase in the expression of DenACS1 and DenACO1 genes. The compatible pollinia induced a negative regulation of DenERS1 which may play an important role in ethylene perception and in modulating ethylene signaling transduction during pollinia-induced flower senescence.

Role of ethylene in ER stress and the unfolded protein response in tomato (Solanum lycopersicum L.) plants

The unfolded protein response (UPR) plays a significant role in the maintenance of cellular homeostasis under endoplasmic reticulum (ER) stress, which is highly dependent on the regulation of defense-related phytohormones. In this study, the role of ethylene (ET) in ER stress and UPR was investigated in the leaves of intact tomato (Solanum lycopersicum) plants. Exogenous application of the ET precursor 1-aminocyclopropane-1-carboxylic acid not only resulted in higher ET emission from leaves but also increased the expression of the UPR marker gene SlBiP and the transcript levels of the ER stress sensor SlIRE1, as well as the levels of SlbZIP60, after 24 h in tomato leaves. Using ET receptor Never ripe (Nr) mutants, a significant role of ET in tunicamycin (Tm)-induced ER stress sensing and signaling was confirmed based on the changes in the expression levels of SlIRE1b and SlBiP. Furthermore, the analysis of other defense-related phytohormones showed that the Tm-induced ET can affect positively the levels of and response to salicylic acid. Additionally, it was found that nitric oxide production and lipid peroxidation, as well as the electrolyte leakage induced by Tm, is regulated by ET, whereas the levels of H₂O₂ and proteolytic activity seemed to be independent of ET under ER stress in the leaves of tomato plants.

Transcriptome analysis of Rafflesia cantleyi flower stages reveals insights into the regulation of senescence

Rafflesia is a unique plant species existing as a single flower and produces the largest flower in the world. While Rafflesia buds take up to 21 months to develop, its flowers bloom and wither within about a week. In this study, transcriptome analysis was carried out to shed light on the molecular mechanism of senescence in Rafflesia. A total of 53.3 million high quality reads were obtained from two Rafflesia cantleyi flower developmental stages and assembled to generate 64,152 unigenes. Analysis of this dataset showed that 5,166 unigenes were differentially expressed, in which 1,073 unigenes were identified as genes involved in flower senescence. Results revealed that as the flowers progress to senescence, more genes related to flower senescence were significantly over-represented compared to those related to plant growth and development. Senescence of the R. cantleyi flower activates senescence-associated genes in the transcription activity (members of the transcription factor families MYB, bHLH, NAC, and WRKY), nutrient remobilization (autophagy-related protein and transporter genes), and redox regulation (CATALASE). Most of the senescence-related genes were found to be differentially regulated, perhaps for the fine-tuning of various responses in the senescing R. cantleyi flower. Additionally, pathway analysis showed the activation of genes such as ETHYLENE RECEPTOR, ETHYLENE-INSENSITIVE 2, ETHYLENE-INSENSITIVE 3, and ETHYLENE-RESPONSIVE TRANSCRIPTION FACTOR, indicating the possible involvement of the ethylene hormone response pathway in the regulation of R. cantleyi senescence. Our results provide a model of the molecular mechanism underlying R. cantleyi flower senescence, and contribute essential information towards further understanding the biology of the Rafflesiaceae family.

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.

Regulation of rose petal dehydration tolerance and senescence by RhNAP transcription factor via the modulation of cytokinin catabolism

Petals and leaves share common evolutionary origins but have different phenotypic characteristics, such as the absence of stomata in the petals of most angiosperm species. Plant NAC transcription factor, NAP, is involved in ABA responses and regulates senescence-associated genes, and especially those that affect stomatal movement. However, the regulatory mechanisms and significance of NAP action in senescing astomatous petals is unclear. A major limiting factor is failure of flower opening and accelerated senescence. Our goal is to understand the finely regulatory mechanism of dehydration tolerance and aging in rose flowers. We functionally characterized RhNAP, an AtNAP-like transcription factor gene that is induced by dehydration and aging in astomatous rose petals. Cytokinins (CKs) are known to delay petal senescence and we found that a cytokinin oxidase/dehydrogenase gene 6 (RhCKX6) shares similar expression patterns with RhNAP. Silencing of RhNAP or RhCKX6 expression in rose petals by virus induced gene silencing markedly reduced petal dehydration tolerance and delayed petal senescence. Endogenous CK levels in RhNAP- or RhCKX6-silenced petals were significantly higher than those of the control. Moreover, RhCKX6 expression was reduced in RhNAP-silenced petals. This suggests that the expression of RhCKX6 is regulated by RhNAP. Yeast one-hybrid experiments and electrophoresis mobility shift assays showed that RhNAP binds to the RhCKX6 promoter in heterologous in vivo system and in vitro, respectively. Furthermore, the expression of putative signal transduction and downstream genes of ABA-signaling pathways were also reduced due to the repression of PP2C homolog genes by RhNAP in rose petals. Taken together, our study indicates that the RhNAP/RhCKX6 interaction represents a regulatory step enhancing dehydration tolerance in young rose petals and accelerating senescence in mature petals in a stomata-independent manner.

Transgenic Kalanchoë blossfeldiana, Containing Individual rol Genes and Open Reading Frames Under 35S Promoter, Exhibit Compact Habit, Reduced Plant Growth, and Altered Ethylene Tolerance in Flowers

Reduced growth habit is a desirable trait for ornamental potted plants and can successfully be obtained through Rhizobium rhizogenes transformation in a stable and heritable manner. Additionally, it can also be obtained by transformation with Agrobacterium tumefaciens harboring specific genes from R. rhizogenes. The bacterial T-DNA harbors four root oncogenic loci (rol) genes and 14 less known open reading frames (ORFs). The four rol genes, i.e., rolA, rolB, rolC, and rolD, are conceived as the common denominator for the compact phenotype and the other less characterized ORFs seem auxiliary but present a potential breeding target for less aberrant and/or more tailored phenotypes. In this study, Kalanchoë blossfeldiana 'Molly' was transformed with individual rol genes and selected ORFs in 35S overexpressing cassettes to comprehensively characterize growth traits, gene copy and expression, and ethylene tolerance of the flowers. An association of reduced growth habit, e.g. height and diameter, was observed for rolB2 and ORF14-2 when a transgene single copy and high gene expression were detected. Chlorophyll content was reduced in overexpressing lines compared to wild type (WT), except for one ΔORF13a (a truncated ORF13a, where SPXX DNA-binding motif is absent). The flower number severely decreased in the overexpressing lines compared to WT. The anthesis timing showed that WT opened the first flower at 68.9 ± 0.9 days and the overexpressing lines showed similar or up to 24 days delay in flowering. In general, a single or low relative gene copy insertion was correlated to higher gene expression, ca. 3 to 5-fold, in rolB and ΔORF13a lines, while in ORF14 such relation was not directly linked. The increased gene expression observed in rolB2 and ΔORF13a-2 contributed to reducing plant growth and a more compact habit. Tolerance of detached flowers to 0.5 μl L-1 ethylene was markedly higher for ORF14 with 66% less flower closure at day 3 compared to WT. The subcellular localization of rolC and ΔORF13a was investigated by transient expression in Nicotiana benthamiana and confocal images showed that rolC and ΔORF13a are soluble and localize in the cytoplasm being able to enter the nucleus.

Comprehensive analysis of sucrolytic enzyme gene families in carnation (Dianthus caryophyllus L.)

Sucrose plays crucial roles in growth and responses of plants to the environment, including those in ornamental species. During post-harvest handling of cut flowers, sucrose degradation is an essential process of inter- and intra-cellular carbon partitioning affecting flower opening and senescence and, subsequently, flower quality. However, complete information about the molecular basis of sucrose degradation in ornamental flowers, which can be catalyzed by two kinds of sucrolytic enzymes, invertase (INV), and sucrose synthase (SUS), is not available from past reports. The present study shows that sucrose treatment of carnation (Dianthus caryophyllus L.) florets increased starch content in petals, accompanied by decreased vacuolar INV (VIN) activity and increased SUS activity. However, hypoxic treatment of carnation florets decreased sucrose content and cell-wall INV (CWIN) activity in petals. In silico analysis using the carnation genome database identified six CWIN, three VIN, eight cytoplasmic INV (CIN), and five SUS genes. Real-time RT-PCR analysis confirmed that these genes are differentially expressed in carnation petals in response to sucrose and hypoxic treatments, partially corresponding to the changes in enzyme activities. In contrast to DcSUS1 (Dca4507.1), a SUS gene already reported in carnation, which showed preferential expression under aerated conditions, the expression of DcSUS2 (Dca22218.1), an undescribed carnation SUS gene, was enhanced under hypoxia similarly to an alcohol dehydrogenase gene DcADH1 (Dca18671.1). These results suggest that sugar metabolism in carnation petals is regulated in response to environmental cues, accompanied by modulated activities and gene expression of a set of sucrolytic enzymes.

Auxin Regulates Sucrose Transport to Repress Petal Abscission in Rose (Rosa hybrida)

Developmental transitions in plants require adequate carbon resources, and organ abscission often occurs due to competition for carbohydrates/assimilates. Physiological studies have indicated that organ abscission may be activated by Suc deprivation; however, an underlying regulatory mechanism that links Suc transport to organ shedding has yet to be identified. Here, we report that transport of Suc and the phytohormone auxin to petals through the phloem of the abscission zone (AZ) decreases during petal abscission in rose (Rosa hybrida), and that auxin regulates Suc transport into the petals. Expression of the Suc transporter RhSUC2 decreased in the AZ during rose petal abscission. Similarly, silencing of RhSUC2 reduced the Suc content in the petals and promotes petal abscission. We established that the auxin signaling protein RhARF7 binds to the promoter of RhSUC2, and that silencing of RhARF7 reduces petal Suc contents and promotes petal abscission. Overexpression of RhSUC2 in the petal AZ restored accelerated petal abscission caused by RhARF7 silencing. Moreover, treatment of rose petals with auxin and Suc delayed ethylene-induced abscission, whereas silencing of RhARF7 and RhSUC2 accelerated ethylene-induced petal abscission. Our results demonstrate that auxin modulates Suc transport during petal abscission, and that this process is regulated by a RhARF7-RhSUC2 module in the AZ.

Seasonal senescence of leaves and roots of Populus trichocarpa-is the scenario the same or different?

The remobilization and resorption of plant nutrients is considered as a crucial aspect of the seasonal senescence of plant organs. In leaves, the mechanisms responsible for the relocation of valuable compounds are well understood while the related processes in roots are still being debated. Some research indicates that remobilization in roots occurs, while other studies have not found evidence of this process. Considering that the total biomass of fine roots is equal to or greater than that of leaves, clarifying the conflicting reports and ambiguities may provide critical information on the circulation of chemical elements in forest ecosystems. This study provides new information concerning the basis for remobilization processes in roots by combining physiological data with gene expression and protein levels. We suggest that, as in leaves, molecular mechanisms involved in nitrogen (N) resorption are also activated in senescent roots. An analysis of N concentration indicated that N levels decreased during the senescence of both organs. The decrease was associated with an increase in the expression of a glutamine synthetase (GS) gene and a concomitant elevation in the amount of GS-one of the most important enzymes in N metabolism. In addition, significant accumulation of carbohydrates was observed in fine roots, which may represent an adaptation to unfavorable weather conditions that would allow remobilization to occur rather than a rapid death in response to ground frost or cold. Our results provide new insights into the senescence of plant organs and clarify contentious topics related to the remobilization process in fine roots.

Overexpression of sugar transporter gene PbSWEET4 of pear causes sugar reduce and early senescence in leaves

As the main energy source for generating ATP during plant growth and development, sugars are synthesized in leaves, while sugar allocation depends on both intracellular transport between different organelles and source-to-sink transport. However, sugar transport related research is limited in pear. Here, a sugar transporter PbSWEET4 was identified that control sugar content and senescence in leaf. Phylogenetic analysis and multiple sequence alignment results indicated that PbSWEET4 was homologous to AtSWEET15, which contained two conserved domains and could promote senescence. The qRT-PCR and transcriptome database result showed that the expression of PbSWEET4 was positively correlated with leaf development, especially highly expressed in older leaves. Furthermore, the evaluation of promoter-GUS activity also indicated that PbSWEET4 exhibited the highest expression level in older leaves. The subcellular localization revealed that the PbSWEET4 localized in the plasma membrane. Finally, overexpression of the PbSWEET4 in strawberry plants could reduce leaf sugar content and chlorophyll content, while accelerate leaf senescence, which might be due to enhanced export of sugars from leaves. These results enrich the knowledge about the function of sugar exporter in regulating the fruit species development, and provide a novel genetic resource for future improvement in carbohydrate partitioning for pear and other fruit trees.

"Help is in the air": volatiles from salt-stressed plants increase the reproductive success of receivers under salinity

Salinity alters VOC profile in emitter sweet basil plants. Airborne signals by emitter plants promote earlier flowering of receivers and increase their reproductive success under salinity. Airborne signals can prime neighboring plants against pathogen and/or herbivore attacks, whilst little is known about the possibility that volatile organic compounds (VOCs) emitted by stressed plants alert neighboring plants against abiotic stressors. Salt stress (50 mM NaCl) was imposed on Ocimum basilicum L. plants (emitters, namely NaCl), and a putative alerting-priming interaction was tested on neighboring basil plants (receivers, namely NaCl-S). Compared with the receivers, the NaCl plants exhibited reduced biomass, lower photosynthesis, and changes in the VOC profile, which are common early responses of plants to salinity. In contrast, NaCl-S plants had physiological parameters similar to those of nonsalted plants (C), but exhibited a different VOC fingerprint, which overlapped, for most compounds, with that of emitters. NaCl-S plants exposed later to NaCl treatment (namely NaCl-S + NaCl) exhibited changes in the VOC profile, earlier plant senescence, earlier flowering, and higher seed yield than C + NaCl plants. This experiment offers the evidence that (1) NaCl-triggered VOCs promote metabolic changes in NaCl-S plants, which, finally, increase reproductive success and (2) the differences in VOC profiles observed between emitters and receivers subjected to salinity raise the question whether the receivers are able to "propagate" the warning signal triggered by VOCs in neighboring companions.

Magnesium Hydride-Mediated Sustainable Hydrogen Supply Prolongs the Vase Life of Cut Carnation Flowers via Hydrogen Sulfide

Magnesium hydride (MgH₂) is a promising solid-state hydrogen source with high storage capacity (7.6 wt%). Although it is recently established that MgH₂ has potential applications in medicine because it sustainably supplies hydrogen gas (H₂), the biological functions of MgH₂ in plants have not been observed yet. Also, the slow reaction kinetics restricts its practical applications. In this report, MgH₂ (98% purity; 0.5-25 μm size) was firstly used as a hydrogen generation source for postharvest preservation of flowers. Compared with the direct hydrolysis of MgH₂ in water, the efficiency of hydrogen production from MgH₂ hydrolysis could be greatly improved when the citrate buffer solution is introduced. These results were further confirmed in the flower vase experiment by showing higher efficiency in increasing the production and the residence time of H₂ in solution, compared with hydrogen-rich water. Mimicking the response of hydrogen-rich water and sodium hydrosulfide (a hydrogen sulfide donor), subsequent experiments discovered that MgH₂-citrate buffer solution not only stimulated hydrogen sulfide (H₂S) synthesis but also significantly prolonged the vase life of cut carnation flowers. Meanwhile, redox homeostasis was reestablished, and the increased transcripts of representative senescence-associated genes, including DcbGal and DcGST1, were partly abolished. By contrast, the discussed responses were obviously blocked by the inhibition of endogenous H₂S with hypotaurine, an H₂S scavenger. These results clearly revealed that MgH₂-supplying H₂ could prolong the vase life of cut carnation flowers via H₂S signaling, and our results, therefore, open a new window for the possible application of hydrogen-releasing materials in agriculture.

Proteome and Ubiquitome Changes during Rose Petal Senescence

Petal senescence involves numerous programmed changes in biological and biochemical processes. Ubiquitination plays a critical role in protein degradation, a hallmark of organ senescence. Therefore, we investigated changes in the proteome and ubiquitome of senescing rose (Rosa hybrida) petals to better understand their involvement in petal senescence. Of 3859 proteins quantified in senescing petals, 1198 were upregulated, and 726 were downregulated during senescence. We identified 2208 ubiquitinated sites, including 384 with increased ubiquitination in 298 proteins and 1035 with decreased ubiquitination in 674 proteins. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that proteins related to peptidases in proteolysis and autophagy pathways were enriched in the proteome, suggesting that protein degradation and autophagy play important roles in petal senescence. In addition, many transporter proteins accumulated in senescing petals, and several transport processes were enriched in the ubiquitome, indicating that transport of substances is associated with petal senescence and regulated by ubiquitination. Moreover, several components of the brassinosteroid (BR) biosynthesis and signaling pathways were significantly altered at the protein and ubiquitination levels, implying that BR plays an important role in petal senescence. Our data provide a comprehensive view of rose petal senescence at the posttranslational level.

RhERF113 Functions in Ethylene-Induced Petal Senescence by Modulating Cytokinin Content in Rose

In rose (Rosa hybrida), flower senescence is accelerated by ethylene and delayed by cytokinins (CTKs). However, the effectors that regulate these processes are not currently understood. In this study, we identified an APETALA2/ethylene-responsive factor (AP2/ERF) gene, RhERF113, which was induced by ethylene and up-regulated during flower senescence in most floral organs, including sepal, petal, stamen and pistil. The virus-induced gene silencing (VIGS) of RhERF113 expression accelerated rose flower senescence, which was accompanied by a lower CTK content in the flowers. This accelerated senescence could be restored by exogenous CTK treatment. Moreover, the expression levels of genes related to CTK biosynthesis and signaling, including ISOPENTENYL TRANSFERASE 5 (RhIPT5), RhIPT8, HISTIDINE KINASE 2 (RhHK2), RhHK3, CYTOKININ RESPONSE REGULATOR 3 (RhCRR3), RhCRR5, RhCRR8, HOMEOBOX PROTEIN 6 (RhHB6) and PATHOGENESIS-RELATED 10.1 (RhPR10.1), were decreased in the RhERF113-silenced rose flowers. Taken together, our results demonstrate that RhERF113 delays ethylene-induced flower senescence by increasing the CTK content of the floral tissues.

The Multifaceted Role of Pectin Methylesterase Inhibitors (PMEIs)

Plant cell walls are complex and dynamic structures that play important roles in growth and development, as well as in response to stresses. Pectin is a major polysaccharide of cell walls rich in galacturonic acid (GalA). Homogalacturonan (HG) is considered the most abundant pectic polymer in plant cell walls and is partially methylesterified at the C6 atom of galacturonic acid. Its degree (and pattern) of methylation (DM) has been shown to affect biomechanical properties of the cell wall by making pectin susceptible for enzymatic de-polymerization and enabling gel formation. Pectin methylesterases (PMEs) catalyze the removal of methyl-groups from the HG backbone and their activity is modulated by a family of proteinaceous inhibitors known as pectin methylesterase inhibitors (PMEIs). As such, the interplay between PME and PMEI can be considered as a determinant of cell adhesion, cell wall porosity and elasticity, as well as a source of signaling molecules released upon cell wall stress. This review aims to highlight recent updates in our understanding of the PMEI gene family, their regulation and structure, interaction with PMEs, as well as their function in response to stress and during development.

Vacuolar processing enzymes, AmVPE1 and AmVPE2, as potential executors of ethylene regulated programmed cell death in the lace plant (Aponogeton madagascariensis)

Perforation formation in Aponogeton madagascariensis (Mirb.) H.Bruggen (lace plant) is an excellent model for studying developmentally regulated programmed cell death (PCD). In this study, we isolated and identified two lace plant vacuolar processing enzymes (VPEs) and investigated their involvement in PCD and throughout leaf development. Lace plant VPE transcript levels were determined during seven different stages of leaf development. PCD and non-PCD cells from “window” stage leaves (in which perforations are forming) were separated through laser-capture microscopy and their transcript levels were also determined. VPE activity was also studied between the cell types, through a VPE activity-based probe JOPD1. Additionally, VPE transcript levels were studied in plants treated with an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG). The two isolated VPEs, AmVPE1 and AmVPE2, are vegetative type VPEs. AmVPE1 had higher transcript levels during a pre-perforation developmental stage, immediately prior to visible signs of PCD. AmVPE2 transcript levels were higher later during window and late window stages. Both VPEs had higher transcript and activity levels in PCD compared with the non-PCD cells. AVG treatment inhibited PCD and associated increases in VPE transcript levels. Our results suggested that VPEs are involved in the execution of the ethylene-related PCD in the lace plant.

Plant organ senescence - regulation by manifold pathways

Senescence is the final stage of plant ontogeny before death. Senescence may occur naturally because of age or may be induced by various endogenous and exogenous factors. Despite its destructive character, senescence is a precisely controlled process that follows a well-defined order. It is often inseparable from programmed cell death (PCD), and a correlation between these processes has been confirmed during the senescence of leaves and petals. Despite suggestions that senescence and PCD are two separate processes, with PCD occurring after senescence, cell death responsible for senescence is accompanied by numerous changes at the cytological, physiological and molecular levels, similar to other types of PCD. Independent of the plant organ analysed, these changes are focused on initiating the processes of cellular structural degradation via fluctuations in phytohormone levels and the activation of specific genes. Cellular structural degradation is genetically programmed and dependent on autophagy. Phytohormones/plant regulators are heavily involved in regulating the senescence of plant organs and can either promote [ethylene, abscisic acid (ABA), jasmonic acid (JA), and polyamines (PAs)] or inhibit [cytokinins (CKs)] this process. Auxins and carbohydrates have been assigned a dual role in the regulation of senescence, and can both inhibit and stimulate the senescence process. In this review, we introduce the basic pathways that regulate senescence in plants and identify mechanisms involved in controlling senescence in ephemeral plant organs. Moreover, we demonstrate a universal nature of this process in different plant organs; despite this process occurring in organs that have completely different functions, it is very similar. Progress in this area is providing opportunities to revisit how, when and which way senescence is coordinated or decoupled by plant regulators in different organs and will provide a powerful tool for plant physiology research.

Transcriptome profiling reveals regulatory mechanisms underlying corolla senescence in petunia

The genetic regulatory mechanisms that govern natural corolla senescence in petunia are not well understood. To identify key genes and pathways that regulate the process, we performed a transcriptome analysis in petunia corolla at four developmental stages, including corolla fully opening without anther dehiscence (D0), corolla expansion, 2 days after anthesis (D2), corolla with initial signs of senescence (D4), and wilting corolla (D7). We identified large numbers of differentially expressed genes (DEGs), ranging from 4626 between the transition from D0 and D2, 1116 between D2 and D4, a transition to the onset of flower senescence, and 327 between D4 and D7, a developmental stage representing flower senescence. KEGG analysis showed that the auxin- and ethylene-related hormone biosynthesis and signaling transduction pathways were significantly activated during the flower development and highly upregulated at onset of flower senescence. Ethylene emission was detected at the D2 to D4 transition, followed by a large eruption at the D4 to D7 transition. Furthermore, large numbers of transcription factors (TFs) were activated over the course of senescence. Functional analysis by virus-induced gene silencing (VIGS) experiments demonstrated that inhibition of the expression of TFs, such as ethylene-related ERF, auxin-related ARF, bHLH, HB, and MADS-box, significantly extended or shortened flower longevity. Our data suggest that hormonal interaction between auxin and ethylene may play critical regulatory roles in the onset of natural corolla senescence in petunia.

Maize susceptibility to Ustilago maydis is influenced by genetic and chemical perturbation of carbohydrate allocation

The ability of biotrophic fungi to metabolically adapt to the host environment is a critical factor in fungal diseases of crop plants. In this study, we analysed the transcriptome of maize tumours induced by Ustilago maydis to identify key features underlying metabolic shifts during disease. Among other metabolic changes, this analysis highlighted modifications during infection in the transcriptional regulation of carbohydrate allocation and starch metabolism. We confirmed the relevance of these changes by establishing that symptom development was altered in an id1 (indeterminate1) mutant that showed increased accumulation of sucrose as well as being defective in the vegetative to reproductive transition. We further established the relevance of specific metabolic functions related to carbohydrate allocation by assaying disease in su1 (sugary1) mutant plants with altered starch metabolism and in plants treated with glucose, sucrose and silver nitrate during infection. We propose that specific regulatory and metabolic changes influence the balance between susceptibility and resistance by altering carbon allocation to promote fungal growth or to influence plant defence. Taken together, these studies reveal key aspects of metabolism that are critical for biotrophic adaptation during the maize-U. maydis interaction.

Synergistic Effect of Nano-Sliver with Sucrose on Extending Vase Life of the Carnation cv. Edun

We investigated the effects of sucrose and nano-silver (NAg) on extending the vase life of cut carnation flowers "Edun". Sucrose (pulse treatment) suppressed ethylene production by downregulating the genes that code for its biosynthesis. Relative to the control, however, sucrose significantly promoted xylem blockage on cut stem surfaces and reduced relative fresh weight, antioxidant activity, and cysteine proteinase inhibitor gene (DcCPi) expression. Consequently, the sucrose-treated flowers had shorter vase lives than the control. In contrast, NAg suppressed ethylene production in the petal, prevented xylem blockage in the cut stem surface, and improved all the aforementioned parameters. Therefore, NAg increased flower longevity. The most effective treatment in terms of longevity extension and parameter improvement, however, was the combination of NAg and sucrose. These results suggest that sucrose can suppress ethylene production but does not necessarily extend the vase life of the flower cultivar. The role of NAg in increasing cut carnation longevity is mainly to inhibit xylem blockage rather than suppress ethylene production, and the combined effect of NAg and sucrose is most effective at prolonging cut carnation vase life, likely due to their synergetic effects on multiple modes of action.

Transcriptome Analysis of Taxillusi chinensis (DC.) Danser Seeds in Response to Water Loss

BACKGROUND

Taxillus chinensis (DC.) Danser, the official species of parasitic loranthus that grows by parasitizing other plants, is used in various traditional Chinese medicine prescriptions. ABA-dependent and ABA-independent pathways are two major pathways in response to drought stress for plants and some genes have been reported to play a key role during the dehydration including dehydration-responsive protein RD22, late embryogenesis abundant (LEA) proteins, and various transcription factors (TFs) like MYB and WRKY. However, genes responding to dehydration are still unknown in loranthus.

METHODS AND RESULTS

Initially, loranthus seeds were characterized as recalcitrant seeds. Then, biological replicates of fresh loranthus seeds (CK), and seeds after being dehydrated for 16 hours (Tac-16) and 36 hours (Tac-36) were sequenced by RNA-Seq, generating 386,542,846 high quality reads. A total of 164,546 transcripts corresponding to 114,971 genes were assembled by Trinity and annotated by mapping them to NCBI non-redundant (NR), UniProt, GO, KEGG pathway and COG databases. Transcriptome profiling identified 60,695, 56,027 and 66,389 transcripts (>1 FPKM) in CK, Tac-16 and Tac-36, respectively. Compared to CK, we obtained 2,102 up-regulated and 1,344 down-regulated transcripts in Tac-16 and 1,649 up-regulated and 2,135 down-regulated transcripts in Tac-36 by using edgeR. Among them some have been reported to function in dehydration process, such as RD22, heat shock proteins (HSP) and various TFs (MYB, WRKY and ethylene-responsive transcription factors). Interestingly, transcripts encoding ribosomal proteins peaked in Tac-16. It is indicated that HSPs and ribosomal proteins may function in early response to drought stress. Raw sequencing data can be accessed in NCBI SRA platform under the accession number SRA309567.

CONCLUSIONS

This is the first time to profile transcriptome globally in loranthus seeds. Our findings provide insights into the gene regulations of loranthus seeds in response to water loss and expand our current understanding of drought tolerance and germination of seeds.

Morphological changes in senescing petal cells and the regulatory mechanism of petal senescence

Petal senescence, or programmed cell death (PCD) in petals, is a developmentally regulated and genetically programmed process. During petal senescence, petal cells show morphological changes associated with PCD: tonoplast rupture and rapid destruction of the cytoplasm. This type of PCD is classified as vacuolar cell death or autolytic PCD based on morphological criteria. In PCD of petal cells, characteristic morphological features including an autophagy-like process, chromatin condensation, and nuclear fragmentation are also observed. While the phytohormone ethylene is known to play a crucial role in petal senescence in some plant species, little is known about the early regulation of ethylene-independent petal senescence. Recently, a NAC (NAM/ATAF1,2/CUC2) transcription factor was reported to control the progression of PCD during petal senescence in Japanese morning glory, which shows ethylene-independent petal senescence. In ethylene-dependent petal senescence, functional analyses of transcription factor genes have revealed the involvement of a basic helix-loop-helix protein and a homeodomain-leucine zipper protein in the transcriptional regulation of the ethylene biosynthesis pathway. Here we review the recent advances in our knowledge of petal senescence, mostly focusing on the morphology of senescing petal cells and the regulatory mechanisms of PCD by senescence-associated transcription factors during petal senescence.

Interaction of plant growth regulators and reactive oxygen species to regulate petal senescence in wallflowers (Erysimum linifolium)

BACKGROUND

In many species floral senescence is coordinated by ethylene. Endogenous levels rise, and exogenous application accelerates senescence. Furthermore, floral senescence is often associated with increased reactive oxygen species, and is delayed by exogenously applied cytokinin. However, how these processes are linked remains largely unresolved. Erysimum linifolium (wallflower) provides an excellent model for understanding these interactions due to its easily staged flowers and close taxonomic relationship to Arabidopsis. This has facilitated microarray analysis of gene expression during petal senescence and provided gene markers for following the effects of treatments on different regulatory pathways.

RESULTS

In detached Erysimum linifolium (wallflower) flowers ethylene production peaks in open flowers. Furthermore senescence is delayed by treatments with the ethylene signalling inhibitor silver thiosulphate, and accelerated with ethylene released by 2-chloroethylphosphonic acid. Both treatments with exogenous cytokinin, or 6-methyl purine (which is an inhibitor of cytokinin oxidase), delay petal senescence. However, treatment with cytokinin also increases ethylene biosynthesis. Despite the similar effects on senescence, transcript abundance of gene markers is affected differentially by the treatments. A significant rise in transcript abundance of WLS73 (a putative aminocyclopropanecarboxylate oxidase) was abolished by cytokinin or 6-methyl purine treatments. In contrast, WFSAG12 transcript (a senescence marker) continued to accumulate significantly, albeit at a reduced rate. Silver thiosulphate suppressed the increase in transcript abundance both of WFSAG12 and WLS73. Activity of reactive oxygen species scavenging enzymes changed during senescence. Treatments that increased cytokinin levels, or inhibited ethylene action, reduced accumulation of hydrogen peroxide. Furthermore, although auxin levels rose with senescence, treatments that delayed early senescence did not affect transcript abundance of WPS46, an auxin-induced gene.

CONCLUSIONS

A model for the interaction between cytokinins, ethylene, reactive oxygen species and auxin in the regulation of floral senescence in wallflowers is proposed. The combined increase in ethylene and reduction in cytokinin triggers the initiation of senescence and these two plant growth regulators directly or indirectly result in increased reactive oxygen species levels. A fall in conjugated auxin and/or the total auxin pool eventually triggers abscission.

Integrating transcriptomic and metabolomic analysis to understand natural leaf senescence in sunflower

Leaf senescence is a complex process, which has dramatic consequences on crop yield. In sunflower, gap between potential and actual yields reveals the economic impact of senescence. Indeed, sunflower plants are incapable of maintaining their green leaf area over sustained periods. This study characterizes the leaf senescence process in sunflower through a systems biology approach integrating transcriptomic and metabolomic analyses: plants being grown under both glasshouse and field conditions. Our results revealed a correspondence between profile changes detected at the molecular, biochemical and physiological level throughout the progression of leaf senescence measured at different plant developmental stages. Early metabolic changes were detected prior to anthesis and before the onset of the first senescence symptoms, with more pronounced changes observed when physiological and molecular variables were assessed under field conditions. During leaf development, photosynthetic activity and cell growth processes decreased, whereas sucrose, fatty acid, nucleotide and amino acid metabolisms increased. Pathways related to nutrient recycling processes were also up-regulated. Members of the NAC, AP2-EREBP, HB, bZIP and MYB transcription factor families showed high expression levels, and their expression level was highly correlated, suggesting their involvement in sunflower senescence. The results of this study thus contribute to the elucidation of the molecular mechanisms involved in the onset and progression of leaf senescence in sunflower leaves as well as to the identification of candidate genes involved in this process.

Programmed Cell Death Progresses Differentially in Epidermal and Mesophyll Cells of Lily Petals

In the petals of some species of flowers, programmed cell death (PCD) begins earlier in mesophyll cells than in epidermal cells. However, PCD progression in each cell type has not been characterized in detail. We separately constructed a time course of biochemical signs and expression patterns of PCD-associated genes in epidermal and mesophyll cells in Lilium cv. Yelloween petals. Before visible signs of senescence could be observed, we found signs of PCD, including DNA degradation and decreased protein content in mesophyll cells only. In these cells, the total proteinase activity increased on the day after anthesis. Within 3 days after anthesis, the protein content decreased by 61.8%, and 22.8% of mesophyll cells was lost. A second peak of proteinase activity was observed on day 6, and the number of mesophyll cells decreased again from days 4 to 7. These biochemical and morphological results suggest that PCD progressed in steps during flower life in the mesophyll cells. PCD began in epidermal cells on day 5, in temporal synchrony with the time course of visible senescence. In the mesophyll cells, the KDEL-tailed cysteine proteinase (LoCYP) and S1/P1 nuclease (LoNUC) genes were upregulated before petal wilting, earlier than in epidermal cells. In contrast, relative to that in the mesophyll cells, the expression of the SAG12 cysteine proteinase homolog (LoSAG12) drastically increased in epidermal cells in the final stage of senescence. These results suggest that multiple PCD-associated genes differentially contribute to the time lag of PCD progression between epidermal and mesophyll cells of lily petals.

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.

RNA-sequencing reveals early, dynamic transcriptome changes in the corollas of pollinated petunias

BACKGROUND

Pollination reduces flower longevity in many angiosperms by accelerating corolla senescence. This response requires hormone signaling between the floral organs and results in the degradation of macromolecules and organelles within the petals to allow for nutrient remobilization to developing seeds. To investigate early pollination-induced changes in petal gene expression, we utilized high-throughput sequencing to identify transcripts that were differentially expressed between corollas of pollinated Petunia × hybrida flowers and their unpollinated controls at 12, 18, and 24 hours after opening.

RESULTS

In total, close to 0.5 billion Illumina 101 bp reads were generated, de novo assembled, and annotated, resulting in an EST library of approximately 33 K genes. Over 4,700 unique, differentially expressed genes were identified using comparisons between the pollinated and unpollinated libraries followed by pairwise comparisons of pollinated libraries to unpollinated libraries from the same time point (i.e. 12-P/U, 18-P/U, and 24-P/U) in the Bioconductor R package DESeq2. Over 500 gene ontology terms were enriched. The response to auxin stimulus and response to 1-aminocyclopropane-1-carboxylic acid terms were enriched by 12 hours after pollination (hap). Using weighted gene correlation network analysis (WGCNA), three pollination-specific modules were identified. Module I had increased expression across pollinated corollas at 12, 18, and 24 h, and modules II and III had a peak of expression in pollinated corollas at 18 h. A total of 15 enriched KEGG pathways were identified. Many of the genes from these pathways were involved in metabolic processes or signaling. More than 300 differentially expressed transcription factors were identified.

CONCLUSIONS

Gene expression changes in corollas were detected within 12 hap, well before fertilization and corolla wilting or ethylene evolution. Significant changes in gene expression occurred at 18 hap, including the up-regulation of autophagy and down-regulation of ribosomal genes and genes involved in carbon fixation. This transcriptomic database will greatly expand the genetic resources available in petunia. Additionally, it will guide future research aimed at identifying the best targets for increasing flower longevity by delaying corolla senescence.

De novo transcriptome analysis of petal senescence in Gardenia jasminoides Ellis

BACKGROUND

The petal senescence of ethylene insensitive species has not been investigated thoroughly while little is known about the temporal and tissue specific expression patterns of transcription factors (TFs) in this developmental process. Even less is known on flower senescence of the ornamental pot plant Gardenia jasminoides, a non climacteric flower with significant commercial value.

RESULTS

We initiated a de novo transcriptome study to investigate the petal senescence in four developmental stages of cut gardenia flowers considering that the visible symptoms of senescence appear within 4 days of flower opening. De novo assembly of transcriptome sequencing resulted in 102,263 contigs with mean length of 360 nucleotides that generated 57,503 unigenes. These were further clustered into 20,970 clusters and 36,533 singletons. The comparison of the consecutive developmental stages resulted in 180 common, differentially expressed unigenes. A large number of Simple Sequence Repeats were also identified comprising a large number of dinucleotides and trinucleotides. The prevailing families of differentially expressed TFs comprise the AP2/EREBP, WRKY and the bHLH. There are 81 differentially expressed TFs when the symptoms of flower senescence become visible with the most prevailing being the WRKY family with 19 unigenes. No other WRKY TFs had been identified up to now in petal senescence of ethylene insensitive species. A large number of differentially expressed genes were identified at the initiation of visible symptoms of senescence compared to the open flower stage indicating a significant shift in the expression profiles which might be coordinated by up-regulated and/or down-regulated TFs. The expression of 16 genes that belong to the TF families of WRKY, bHLH and the ethylene sensing pathway was validated using qRT--PCR.

CONCLUSION

This de novo transcriptome analysis resulted in the identification of TFs with specific temporal expression patterns such as two WRKYs and one bHLH, which might play the role of senescence progression regulators. Further research is required to investigate their role in gardenia flowers in order to develop tools to delay petal senescence.

Length of the dark period affects flower opening and the expression of circadian-clock associated genes as well as xyloglucan endotransglucosylase/hydrolase genes in petals of morning glory (Ipomoea nil)

We isolated differentially expressed and dark-responsive genes during flower development and opening in petals of morning glory. Flower opening usually depends on petal expansion and is regulated by both genetic and environmental factors. Flower opening in morning glory (Ipomoea nil) is controlled by the dark/light regime just prior to opening. Opening was normal after 8- or 12-h dark periods but progressed very slowly after a 4-h dark period or in continuous light. Four genes (InXTH1-InXTH4) encoding xyloglucan endotransglucosylase/hydrolases (XTHs) and three genes (InEXPA1-InEXPA3) encoding alpha-expansins (EXPAs) were isolated. The expression patterns of InXTH2, InXTH3, and InXTH4 in petals were closely correlated with the rate of flower opening controlled by the length of the dark period prior to opening, but those of the EXPA genes were not. The expression pattern of InXTH1 gene was closely correlated with petal elongation. Suppression subtractive hybridization was used to isolate dark-responsive genes accompanying flower opening. The expressions of ten isolated genes were associated with the length of the dark period prior to flower opening. One gene was highly homologous to Arabidopsis pseudo-response regulator7, which is associated with the circadian clock and phytochrome signaling; another to Arabidopsis REVEILLE1, which affects the output of the circadian clock. Other genes were related to light responses, plant hormone effects and signal transduction. The possible roles of these genes in regulation of flower opening are discussed.

Transcriptomic analysis of cut tree peony with glucose supply using the RNA-Seq technique

Several unigenes encoding ACS and ERF involved in ethylene biosynthesis and signal transduction were greatly down-regulated in the petal transcriptome of cut tree peony 'Luoyang Hong' with glucose treatment. Glucose also repressed stress-related transcription factor genes DREB, CBF, NAC, WRKY and bHLH. Tree peony (Paeonia suffruticosa Andrews) is a famous traditional flower in China. Glucose supply prolonging vase life of cut tree peony flowers is associated with its role in the suppression of sensitivity to ethylene and ethylene production, but the regulation mechanism of sugar on ethylene biosynthesis and signaling is unclear. In the present work, a normalized cDNA pool was constructed as the reference transcriptome from mixed petals of different developmental cut tree peony 'Luoyang Hong' and sequenced using the Illumina HiSeq™ 2000 platform. We obtained 33,117 unigenes annotated with public protein databases. In addition, the transcriptome change in petals of cut tree peony with glucose supply and the control treatment was investigated. With non-redundant annotation, 173 differentially expressed genes were identified, with 41 up-regulated genes and 132 down-regulated genes. According to RNA-Seq data and real-time quantitative polymerase chain reaction validation, one unigene encoding ACS, a key ethylene synthetic enzyme, and four unigenes encoding ERF, which is involved in ethylene signal transduction was greatly down-regulated with glucose treatment. Furthermore, stress-related transcription factor genes DREB, CBF, NAC, WRKY and bHLH were also repressed with glucose supply, as well as several other stress-responsive and stress-tolerance genes, indicating that glucose supply probably releases the effects induced by various environmental stress. All the results and analysis are valuable resources for better understanding of the beneficial influence of exogenous sugars on cut tree peony.

Sequence analysis of the genome of carnation (Dianthus caryophyllus L.)

The whole-genome sequence of carnation (Dianthus caryophyllus L.) cv. ‘Francesco’ was determined using a combination of different new-generation multiplex sequencing platforms. The total length of the non-redundant sequences was 568 887 315 bp, consisting of 45 088 scaffolds, which covered 91% of the 622 Mb carnation genome estimated by k-mer analysis. The N50 values of contigs and scaffolds were 16 644 bp and 60 737 bp, respectively, and the longest scaffold was 1 287 144 bp. The average GC content of the contig sequences was 36%. A total of 1050, 13, 92 and 143 genes for tRNAs, rRNAs, snoRNA and miRNA, respectively, were identified in the assembled genomic sequences. For protein-encoding genes, 43 266 complete and partial gene structures excluding those in transposable elements were deduced. Gene coverage was ∼98%, as deduced from the coverage of the core eukaryotic genes. Intensive characterization of the assigned carnation genes and comparison with those of other plant species revealed characteristic features of the carnation genome. The results of this study will serve as a valuable resource for fundamental and applied research of carnation, especially for breeding new carnation varieties. Further information on the genomic sequences is available at http://carnation.kazusa.or.jp.

TaEIL1, a wheat homologue of AtEIN3, acts as a negative regulator in the wheat-stripe rust fungus interaction

Transcription factors (TFs) play crucial roles in the transcriptional regulation of plant development and defence responses. Increasing evidence has implicated ETHYLENE INSENSITIVE3 (EIN3) in the plant defence response to pathogen infection and environmental stimuli. However, the role of EIN3 in wheat resistance to Puccinia striiformis f. sp. tritici (Pst) is not clear. Here, TaEIL1 was isolated by rapid amplification of cDNA ends (RACE) based on a sequence fragment from a wheat-Pst interaction cDNA library. The TaEIL1 protein contains a typical EIN3-binding domain, and transient expression analyses indicated that TaEIL1 is localized in the nucleus. Yeast one-hybrid assay revealed that TaEIL1 exhibits transcriptional activity, and its C-terminus is necessary for the activation of transcription. TaEIL1 transcripts were regulated by environmental stress stimuli and were decreased under salicylic acid (SA) treatment. When wheat leaves were challenged with Pst, the transcript level of TaEIL1 in the compatible interaction was approximately three times higher than that in the incompatible interaction. Knocking down TaEIL1 through the Barley stripe mosaic virus (BSMV) virus-induced gene silencing (VIGS) system attenuated the growth of Pst, with shortened hyphae and reduced hyphal branches, haustorial mother cells and colony size. Moreover, enhanced necrosis was triggered by the Pst avirulent race CYR23, indicating that the hypersensitive response was strengthened in TaEIL1-silenced wheat plants. Thus, the up-regulation of defence-related genes and increased sucrose abundance might contribute to the enhanced disease resistance of wheat to the virulent race CYR31. Taken together, the results suggested that the suppression of TaEIL1 transcripts could enhance the resistance of wheat to stripe rust fungus.

Phytohormone and assimilate profiles in emasculated flowers of the black locust (Robinia pseudoacacia) during development

Emasculation and bagging of flowers, which are widely used in the controlled pollination of monoclinous plants, may induce premature senescence, flower abscission and low fruit set. To determine the mechanism responsible for these phenomena, levels of abscisic acid (ABA), jasmonic acid (JA), indole-3-acetic acid (IAA), ethylene, soluble sugars, reducing sugars and free amino acids in black locust (Robinia pseudoacacia) flowers subjected to different treatments were quantified at different developmental stages. The phytohormones and assimilates were also quantified in untreated flowers to investigate the presence of discernible patterns. The levels of ethylene and ABA in emasculated and bagged (EB) flowers increased prematurely compared with those of untreated flowers, whereas the content of reducing sugars in EB flowers decreased compared with that of untreated flowers. These results indicated that the premature increase in ethylene and ABA synthesis, and the decrease in reducing sugars content, in EB flowers may cause flower abscission and result in low fruit set, which may be relevant for assimilate applications and future research on the regulation of controlled pollinations with exogenous phytohormones.

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.

From models to ornamentals: how is flower senescence regulated?

Floral senescence involves an ordered set of events coordinated at the plant, flower, organ and cellular level. This review assesses our current understanding of the input signals, signal transduction and cellular processes that regulate petal senescence and cell death. In many species a visible sign of petal senescence is wilting. This is accompanied by remobilization of nutrients from the flower to the developing ovary or to other parts of the plant. In other species, petals abscise while still turgid. Coordinating signals for floral senescence also vary across species. In some species ethylene acts as a central regulator, in others floral senescence is ethylene insensitive and other growth regulators are implicated. Due to the variability in this coordination and sequence of events across species, identifying suitable models to study petal senescence has been challenging, and the best candidates are reviewed. Transcriptomic studies provide an overview of the MAP kinases and transcription factors that are activated during petal senescence in several species including Arabidopsis. Our understanding of downstream regulators such as autophagy genes and proteases is also improving. This gives us insights into possible signalling cascades that regulate initiation of senescence and coordination of cell death processes. It also identifies the gaps in our knowledge such as the role of microRNAs. Finally future prospects for using all this information from model to non-model species to extend vase life in ornamental species is reviewed.

Transcriptome changes associated with delayed flower senescence on transgenic petunia by inducing expression of etr1-1, a mutant ethylene receptor

Flowers of ethylene-sensitive ornamental plants transformed with ethylene-insensitive 1-1(etr1-1), a mutant ethylene receptor first isolated from Arabidopsis, are known to have longer shelf lives. We have generated petunia plants in which the etr1-1 gene was over-expressed under the control of a chemically-inducible promoter, which would allow expression of etr1-1 to be initiated at the desired time and stage of development. Here, we showed that transgenic plants grew and developed normally without a chemical inducer. Semi-quantitative RT-PCR demonstrated that the abundance of transcripts of Arabidopsis etr1-1 gene was substantially induced in flowers with 30 μM dexamethasone (DEX). Consequently, t he life of the flowers was almost doubled and the peak of ethylene production was delayed. We compared gene expression changes of petals with DEX to those without DEX at 24 h and 48 h by microarray. Our results indicated that transcripts of many putative genes encoding transcription factors were down-regulated by etr1-1 induced expression at the early stage. In addition, putative genes involved in gibberellin biosynthesis, response to jasmonic acid/gibberellins stimulus, cell wall modification, ethylene biosynthesis, and cell death were down-regulated associating with etr1-1 induced expression. We investigated time-course gene expression profiles and found two profiles which displayed totally opposite expression patterns under these two treatments. In these profiles, 'the regulation of transcription' was predominant in GO categories. Taking all results together, we concluded those transcription factors down-regulated at early stage might exert a major role in regulating the senescence process which were consequently characterized by cell wall modification and cell death.

Mineral nutrient remobilization during corolla senescence in ethylene-sensitive and -insensitive flowers

The flower has a finite lifespan that is controlled largely by its role in sexual reproduction. Once the flower has been pollinated or is no longer receptive to pollination, the petals are programmed to senesce. A majority of the genes that are up-regulated during petal senescence, in both ethylene-sensitive and -insensitive flowers, encode proteins involved in the degradation of nucleic acids, proteins, lipids, fatty acids, and cell wall and membrane components. A smaller subset of these genes has a putative role in remobilizing nutrients, and only a few of these have been studied in detail. During senescence, carbohydrates (primarily sucrose) are transported from petals, and the degradation of macromolecules and organelles also allows the plant to salvage mineral nutrients from the petals before cell death. The remobilization of mineral nutrients from a few species has been investigated and will be reviewed in this article. Ethylene's role in nutrient remobilization is discussed by comparing nutrient changes during the senescence of ethylene-sensitive and -insensitive flowers, and by studies in transgenic petunias (Petunia × hybrida) that are insensitive to ethylene. Gene expression studies indicate that remobilization is a key feature of senescence, but some senescence-associated genes have different expression in leaves and petals. These gene expression patterns, along with differences in the nutrient content of leaves and petals, suggest that there are differences in the mechanisms of cellular degradation and nutrient transport in vegetative and floral organs. Autophagy may be the mechanism for large-scale degradation that allows for recycling during senescence, but it is unclear if this causes cell death. Future research should focus on autophagy and the regulation of ATG genes by ethylene during both leaf and petal senescence. We must identify the mechanisms by which individual mineral nutrients are transported out of senescing corollas in both ethylene-sensitive and -insensitive species.

Transcriptome analysis of carnation (Dianthus caryophyllus L.) based on next-generation sequencing technology

Background

Carnation (Dianthus caryophyllus L.), in the family Caryophyllaceae, can be found in a wide range of colors and is a model system for studies of flower senescence. In addition, it is one of the most important flowers in the global floriculture industry. However, few genomics resources, such as sequences and markers are available for carnation or other members of the Caryophyllaceae. To increase our understanding of the genetic control of important characters in carnation, we generated an expressed sequence tag (EST) database for a carnation cultivar important in horticulture by high-throughput sequencing using 454 pyrosequencing technology.

Results

We constructed a normalized cDNA library and a 3’-UTR library of carnation, obtaining a total of 1,162,126 high-quality reads. These reads were assembled into 300,740 unigenes consisting of 37,844 contigs and 262,896 singlets. The contigs were searched against an Arabidopsis sequence database, and 61.8% (23,380) of them had at least one BLASTX hit. These contigs were also annotated with Gene Ontology (GO) and were found to cover a broad range of GO categories. Furthermore, we identified 17,362 potential simple sequence repeats (SSRs) in 14,291 of the unigenes. We focused on gene discovery in the areas of flower color and ethylene biosynthesis. Transcripts were identified for almost every gene involved in flower chlorophyll and carotenoid metabolism and in anthocyanin biosynthesis. Transcripts were also identified for every step in the ethylene biosynthesis pathway.

Conclusions

We present the first large-scale sequence data set for carnation, generated using next-generation sequencing technology. The large EST database generated from these sequences is an informative resource for identifying genes involved in various biological processes in carnation and provides an EST resource for understanding the genetic diversity of this plant.

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.

Sucrose accelerates flower opening and delays senescence through a hormonal effect in cut lily flowers

Sugars are generally used to extend the vase life of cut flowers. Such beneficial effects have been associated with an improvement of water relations and an increase in available energy for respiration by floral tissues. In this study we aimed at evaluating to what extent (i) endogenous levels of sugars in outer and inner tepals, androecium and gynoecium are altered during opening and senescence of lily flowers; (ii) sugar levels increase in various floral tissues after sucrose addition to the vase solution; and (iii) sucrose addition alters the hormonal balance of floral tissues. Results showed that endogenous glucose levels increased during flower opening and decreased during senescence in all floral organs, while sucrose levels increased in outer and inner tepals and the androecium during senescence. Sucrose treatment accelerated flower opening, and delayed senescence, but did not affect tepal abscission. Such effects appeared to be exerted through a specific increase in the endogenous levels of sucrose in the gynoecium and of glucose in all floral tissues. The hormonal balance was altered in the gynoecium as well as in other floral tissues. Aside from cytokinin and auxin increases in the gynoecium; cytokinins, gibberellins, abscisic acid and salicylic acid levels increased in the androecium, while abscisic acid decreased in outer tepals. It is concluded that sucrose addition to the vase solution exerts an effect on flower opening and senescence by, among other factors, altering the hormonal balance of several floral tissues.

Glucose and ethylene signalling pathways converge to regulate trans-differentiation of epidermal transfer cells in Vicia narbonensis cotyledons

Transfer cells are specialized transport cells containing invaginated wall ingrowths that provide an amplified plasma membrane surface area with high densities of transporter proteins. They trans-differentiate from differentiated cells at sites where enhanced rates of nutrient transport occur across apo/symplasmic boundaries. Despite their physiological importance, the signal(s) and signalling cascades responsible for initiating their trans-differentiation are poorly understood. In culture, adaxial epidermal cells of Vicia narbonensis cotyledons were induced to trans-differentiate to a transfer cell morphology. Manipulating their intracellular glucose concentrations by transgenic knock-down of ADP-glucose pyrophosphorylase expression and/or culture on a high-glucose medium demonstrated that glucose functioned as a negative regulator of wall ingrowth induction. In contrast, glucose had no detectable effect on wall ingrowth morphology. The effect on wall ingrowth induction of culture on media containing glucose analogues suggested that glucose acts through a hexokinase-dependent signalling pathway. Elevation of an epidermal cell-specific ethylene signal alone, or in combination with glucose analogues, countered the negative effect of glucose on wall ingrowth induction. Glucose modulated the amplitude of ethylene-stimulated wall ingrowth induction by down-regulating the expression of ethylene biosynthetic genes and an ethylene insensitive 3 (EIN3)-like gene (EIL) encoding a key transcription factor in the ethylene signalling cascade. A model is presented describing the interaction between glucose and ethylene signalling pathways regulating the induction of wall ingrowth formation in adaxial epidermal cells.