Exogenous Eethylene influences flower opening of cut roses (Rosa hybrida) by regulating the genes encoding ethylene biosynthesis enzymes

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.

ACC SYNTHASE4 inhibits gibberellin biosynthesis and FLOWERING LOCUS T expression during citrus flowering

Flowering is an essential process in fruit trees. Flower number and timing have a substantial impact on the yield and maturity of fruit. Ethylene and gibberellin (GA) play vital roles in flowering, but the mechanism of coordinated regulation of flowering in woody plants by GA and ethylene is still unclear. In this study, a lemon (Citrus limon L. Burm) 1-aminocyclopropane-1-carboxylic acid synthase gene (CiACS4) was overexpressed in Nicotiana tabacum and resulted in late flowering and increased flower number. Further transformation of citrus revealed that ethylene and starch content increased, and soluble sugar content decreased in 35S:CiACS4 lemon. Inhibition of CiACS4 in lemon resulted in effects opposite to that of 35S:CiACS4 in transgenic plants. Overexpression of the CiACS4-interacting protein ETHYLENE RESPONSE FACTOR3 (CiERF3) in N. tabacum resulted in delayed flowering and more flowers. Further experiments revealed that the CiACS4-CiERF3 complex can bind the promoters of FLOWERING LOCUS T (CiFT) and GOLDEN2-LIKE (CiFE) and suppress their expression. Moreover, overexpression of CiFE in N. tabacum led to early flowering and decreased flowers, and ethylene, starch, and soluble sugar contents were opposite to those in 35S:CiACS4 transgenic plants. Interestingly, CiFE also bound the promoter of CiFT. Additionally, GA3 and 1-aminocyclopropanecarboxylic acid (ACC) treatments delayed flowering in adult citrus, and treatment with GA and ethylene inhibitors increased flower number. ACC treatment also inhibited the expression of CiFT and CiFE. This study provides a theoretical basis for the application of ethylene to regulate flower number and mitigate the impacts of extreme weather on citrus yield due to delayed flowering.

Two transcription factors, RhERF005 and RhCCCH12, regulate rose resistance to Botrytis cinerea by modulating cytokinin levels

Gray mold caused by the necrotrophic fungal pathogen Botrytis cinerea is one of the most destructive diseases in rose (Rosa spp.). Rose infection by B. cinerea leads to severe economic losses due to necrosis, tissue collapse, and rot. In rose, cytokinins (CKs) positively regulate a defense response to B. cinerea, but little is known about the underlying molecular mechanisms. Here, we characterized two ethylene/jasmonic acid-regulated transcription factors, RhEFR005 and RhCCCH12, that bind to the promoter region of PATHOGENESIS-RELATED 10.1 (RhPR10.1) and promote its transcription, leading to decreased susceptibility to B. cinerea. The RhEFR005/RhCCCH12-RhPR10.1 module regulated cytokinin content in rose, and the susceptibility of RhEFR005-, RhCCCH12-, and RhPR10.1-silenced rose petals can be rescued by exogenous CK. In summary, our results reveal that the RhERF005/RhCCCH12-RhPR10.1 module regulates the CK-induced defense response of rose to B. cinerea.

Expression of ethylene biosynthetic genes during flower senescence and in response to ethephon and silver nitrate treatments in Osmanthus fragrans

BACKGROUND

Sweet osmanthus (Osmanthus fragrans) is an ornamental evergreen tree species in China, whose flowers are sensitive to ethylene. The synthesis of ethylene is controlled by key enzymes and restriction enzymes, 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), which are encoded by multigene families. However, the key synthase responsible for ethylene regulation in O. fragrans is still unknown.

OBJECTIVE

This study aims to screen the key ethylene synthase genes of sweet osmanthus flowers in response to ethylene regulation.

METHODS

In this study, we used the ACO and ACS sequences of Arabidopsis thaliana to search for homologous genes in the O. fragrans petal transcriptome database. These genes were also analyzed bioinformatically. Finally, the expression levels of O. fragrans were compared before and after senescence, as well as after ethephon and silver nitrate treatments.

RESULTS

The results showed that there are five ACO genes and one ACS gene in O. fragrans transcriptome database, and the phylogenetic tree revealed that the proteins encoded by these genes had high homology to the ACS and ACO proteins in plants. Sequence alignment shows that the OfACO1-5 proteins have the 2OG-Fe(II) oxygenase domain, while OfACS1 contains seven conserved domains, as well as conserved amino acids in transaminases and glutamate residues related to substrate specificity. Expression analysis revealed that the expression levels of OfACS1 and OfACO1-5 were significantly higher at the early senescence stage compared to the full flowering stage. The transcripts of the OfACS1, OfACO2, and OfACO5 genes were upregulated by treatment with ethephon. However, out of these three genes, only OfACO2 was significantly downregulated by treatment with AgNO3.

CONCLUSION

Our study found that OfACO2 is an important synthase gene in response to ethylene regulation in sweet osmanthus, which would provide valuable data for further investigation into the mechanisms of ethylene-induced senescence in sweet osmanthus flowers.

Investigating the ecological implications of nanomaterials: Unveiling plants' notable responses to nano-pollution

The rapid advancement of nanotechnology has led to unprecedented innovations; however, it is crucial to analyze its environmental impacts carefully. This review thoroughly examines the complex relationship between plants and nanomaterials, highlighting their significant impact on ecological sustainability and ecosystem well-being. This study investigated the response of plants to nano-pollution stress, revealing the complex regulation of defense-related genes and proteins, and highlighting the sophisticated defense mechanisms in nature. Phytohormones play a crucial role in the complex molecular communication network that regulates plant responses to exposure to nanomaterials. The interaction between plants and nano-pollution influences plants' complex defense strategies. This reveals the interconnectedness of systems of nature. Nevertheless, these findings have implications beyond the plant domain. The incorporation of hyperaccumulator plants into pollution mitigation strategies has the potential to create more environmentally sustainable urban landscapes and improve overall environmental resilience. By utilizing these exceptional plants, we can create a future in which cities serve as centers of both innovation and ecological balance. Further investigation is necessary to explore the long-term presence of nanoparticles in the environment, their ability to induce genetic changes in plants over multiple generations, and their overall impact on ecosystems. In conclusion, this review summarizes significant scientific discoveries with broad implications beyond the confines of laboratories. This highlights the importance of understanding the interactions between plants and nanomaterials within the wider scope of environmental health. By considering these insights, we initiated a path towards the responsible utilization of nanomaterials, environmentally friendly management of pollution, and interdisciplinary exploration. We have the responsibility to balance scientific advancement and environmental preservation to create a sustainable future that combines nature's wisdom with human innovation.

The CALCINEURIN B-LIKE 4/CBL-INTERACTING PROTEIN 3 module degrades repressor JAZ5 during rose petal senescence

Flower senescence is genetically regulated and developmentally controlled. The phytohormone ethylene induces flower senescence in rose (Rosa hybrida), but the underlying signaling network is not well understood. Given that calcium regulates senescence in animals and plants, we explored the role of calcium in petal senescence. Here, we report that the expression of calcineurin B-like protein 4 (RhCBL4), which encodes a calcium receptor, is induced by senescence and ethylene signaling in rose petals. RhCBL4 interacts with CBL-interacting protein kinase 3 (RhCIPK3), and both positively regulate petal senescence. Furthermore, we determined that RhCIPK3 interacts with the jasmonic acid response repressor jasmonate ZIM-domain 5 (RhJAZ5). RhCIPK3 phosphorylates RhJAZ5 and promotes its degradation in the presence of ethylene. Our results reveal that the RhCBL4-RhCIPK3-RhJAZ5 module mediates ethylene-regulated petal senescence. These findings provide insights into flower senescence, which may facilitate innovations in postharvest technology for extending rose flower longevity.

The ARF2-MYB6 module mediates auxin-regulated petal expansion in rose

In cut rose (Rosa hybrida), the flower-opening process is closely associated with vase life. Auxin induces the expression of transcription factor genes that function in petal growth via cell expansion. However, the molecular mechanisms underlying the auxin effect during flower opening are not well understood. Here, we identified the auxin-inducible transcription factor gene RhMYB6, whose expression level is high during the early stages of flower opening. Silencing of RhMYB6 delayed flower opening by controlling petal cell expansion through down-regulation of cell expansion-related genes. Furthermore, we demonstrated that the auxin response factor RhARF2 directly interacts with the promoter of RhMYB6 and represses its transcription. Silencing of RhARF2 resulted in larger petal size and delayed petal movement. We also showed that the expression of genes related to ethylene and petal movement showed substantial differences in RhARF2-silenced petals. Our results indicate that auxin-regulated RhARF2 is a critical player that controls flower opening by governing RhMYB6 expression and mediating the crosstalk between auxin and ethylene signaling.

Comparative genomics analysis of WAK/WAKL family in Rosaceae identify candidate WAKs involved in the resistance to Botrytis cinerea

BACKGROUND

Wall associated kinase (WAK) and WAK-like (WAKL) are typical pattern recognition receptors act as the first sentry of plant defense. But little of WAK/WAKL family is known in Rosaceae.

RESULTS

In this study, 131 WAK/WAKL genes from apple, peach and strawberry were identified using a bioinformatics approach. Together with 68 RcWAK/RcWAKL in rose, we performed a comparative analysis of 199 WAK/WAKL in four Rosaceae crops. The phylogenetic analysis divided all the WAK/WAKL into five clades. Among them, the cis-elements of Clade II and Clade V promoters were enriched in jasmonic acid (JA) signaling and abiotic stress, respectively. And this can also be verified by the rose transcriptome responding to different hormone treatments. WAK/WAKL families have experienced a considerable proportion of purifying selection during evolution, but still 26 amino acid sites evolved under positive selection, which focused on extracellular conserved domains. WAK/WAKL genes presented collinearity relationship within and between crops, throughout four crops we mined four orthologous groups (OGs). The WAK/WAKL genes in OG1 and OG4 were speculated to involve in plant-Botrytis cinerea interaction, which were validated in rose via VIGS as well as strawberry by qRT-PCR.

CONCLUSIONS

These results not only provide genetic resources and valuable information for the evolutionary relationship of WAK/WAKL gene family, but also offer a reference for future in-depth studies of Rosaceae WAK/WAKL genes.

Comparative transcriptome analysis to reveal key ethylene genes involved in a Lonicera macranthoides mutant

BACKGROUND

Lonicera macranthoides Hand.-Mazz. is an important medicinal plant. Xianglei-type (XL) L. macranthoides was formed after many years of cultivation by researchers on the basis of the natural mutant. The corolla of L. macranthoides XL remains unexpanded and its flowering period is nearly three times longer than that of wild-type (WT) plants. However, the molecular mechanism behind this desirable trait remains a mystery.

OBJECTIVE

To understand the floral phenotype differences between L. macranthoides and L. macranthoides XL at the molecular level.

METHODS

Transcriptome analysis was performed on L. macranthoides XL and WT. One DEG was cloned by RT-PCR amplification and selected for qRT-PCR analysis.

RESULTS

Transcriptome analysis showed that there were 5603 differentially expressed genes (DEGs) in XL vs. WT. Enrichment analysis of DEGs showed that pathways related to plant hormone signal transduction were significantly enriched. We identified 23 key genes in ethylene biosynthesis and signal transduction pathways. The most abundant were the ethylene biosynthesis DEGs. In addition, the open reading frames (ORFs) of WT and XL ETR2 were successfully cloned and named LM-ETR2 (GenBank: MW334978) and LM-XL-ETR2 (GenBank: MW334978), respectively. qRT-PCR at different flowering stages suggesting that ETR2 acts in the whole stage of flower development of WT and XL.

CONCLUSIONS

This study provides new insight into the molecular mechanism that regulates the development of special traits in the flowers of L. macranthoides XL. The plant hormone ethylene plays an important role in flower development and flowering duration prolongation in L. macranthoides. The ethylene synthesis gene could be more responsible for the flower phenotype of XL. The genes identified here can be used for breeding and improvement of other flowering plants after functional verification.

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.

Transcriptome analysis of critical genes related to flowering in Mikania micrantha at different altitudes provides insights for a potential control

BACKGROUND

Mikania micrantha is a vine with strong invasion ability, and its strong sexual reproduction ability is not only the main factor of harm, but also a serious obstacle to control. M. micrantha spreads mainly through seed production. Therefore, inhibiting the flowering and seed production of M. micrantha is an effective strategy to prevent from continuing to spread.

RESULT

The flowering number of M. micrantha is different at different altitudes. A total of 67.01 Gb of clean data were obtained from nine cDNA libraries, and more than 83.47% of the clean reads were mapped to the reference genome. In total, 5878 and 7686 significantly differentially expressed genes (DEGs) were found in E2 vs. E9 and E13 vs. E9, respectively. Based on the background annotation and gene expression, some candidate genes related to the flowering pathway were initially screened, and their expression levels in the three different altitudes in flower bud differentiation showed the same trend. That is, at an altitude of 1300 m, the flower integration gene and flower meristem gene were downregulated (such as SOC1 and AP1), and the flowering inhibition gene was upregulated (such as FRI and SVP). Additionally, the results showed that there were many DEGs involved in the hormone signal transduction pathway in the flower bud differentiation of M. micrantha at different altitudes.

CONCLUSIONS

Our results provide abundant sequence resources for clarifying the underlying mechanisms of flower bud differentiation and mining the key factors inhibiting the flowering and seed production of M. micrantha to provide technical support for the discovery of an efficient control method.

Rose WRKY13 promotes disease protection to Botrytis by enhancing cytokinin content and reducing abscisic acid signaling

The plant hormones cytokinin (CK) and abscisic acid (ABA) play critical and often opposite roles during plant growth, development, and responses to abiotic and biotic stresses. Rose (Rosa sp.) is an economically important ornamental crop sold as cut flowers. Rose petals are extremely susceptible to gray mold disease caused by the necrotrophic fungal pathogen Botrytis cinerea. The infection of rose petals by B. cinerea leads to tissue collapse and rot, causing severe economic losses. In this study, we showed that CK and ABA play opposite roles in the susceptibility of rose to B. cinerea. Treatment with CK enhanced the disease protection of rose petals to B. cinerea, while ABA promoted disease progression. We further demonstrated that rose flowers activate CK-mediated disease protection via a B. cinerea-induced rose transcriptional repressor, Rosa hybrida (Rh)WRKY13, which is an ortholog of Arabidopsis (Arabidopsis thaliana), AtWRKY40. RhWRKY13 binds to promoter regions of the CK degradation gene CKX3 (RhCKX3) and the ABA-response gene ABA insensitive4 (RhABI4), leading to simultaneous inhibition of their expression in rose petals. The increased CK content and reduced ABA responses result in enhanced protection from B. cinerea. Collectively, these data reveal opposite roles for CK and ABA in the susceptibility of rose petals against B. cinerea infection, which is mediated by B. cinerea-induced RhWRKY13 expression.

Disruption of transcription factor RhMYB123 causes the transformation of stamen to malformed petal in rose (Rosa hybrida)

We find that the R2R3 MYB transcription factor RhMYB123 has a novel function to regulate stamen-petal organ specification in rose. Rose is one of the ornamental plants with economic importance worldwide. Malformed flower seriously affects the ornamental value and fertility of rose. However, the regulatory mechanism is largely unknown. In this work, we identified a R2R3 MYB transcription factor RhMYB123 from rose, the expression of which significantly decreased from flower differentiation stage to floral organ development stage. Phylogenetic analysis indicated that it belongs to the same subgroup as MYB123 of Arabidopsis and located in nucleus. In addition, RhMYB123 was confirmed to have transcriptional activation function by dual luciferase assay. Silencing RhMYB123 using Virus-Induced Gene Silencing (VIGS) in rose could increase the number of malformed petaloid stamen. Furthermore, we identified 549 differential expressed genes (DEGs) in TRV-RhMYB123 lines compared to TRV controls by RNA-seq of floral buds (flower differentiation stage). Among of those genes, expression of 3 MADS box family genes related to floral organ development reduced in TRV-RhMYB123 lines, including AGAMOUS (RhAG), AGAMOUS LIKE 15 (RhAGL15), and SHATTERPROOF 1 (RhSHP1). Given, previous studies have shown that auxin plays a crucial role in floral meristem initiation and stamen-petal organ specification. We also found 6 DEGs were involved in auxin signal transduction, of which five were reduced expression in TRV-RhMYB123. Taken together, our findings suggested that RhMYB123 may govern the development of malformed petaloid stamen by regulating the expressions of some MADS box family members and auxin signaling pathway elements.

Transcriptomic profiling of rose flower under treatment of various phytohormones and plant growth regulators

Rose is one of the most important ornamental plants, accounting for one-third of the world's fresh cut flower market. The vase life refers to the period of a cut flower retaining its appearance in a vase. During this period, the rose was subjected to a variety of abiotic and biotic stresses, resulting in a reduction in the life of cut flowers. Numerous studies have been carried out on cut rose, which proves the effects of various plant hormones on post-harvest dehydration, petal senescence and abscission, disease and vase life of cut rose flowers. In addition, the natural or synthetic hormones or its inhibitor have been successfully used in cut flower preservatives to extend the vase life of rose. However, there is still a lack of systematic and in-depth research on the expression of rose genes related to plant hormone response. Here we analyzed the gene expression changes of the rose flower under treatment of 11 different plant hormones or its inhibitors in order to provide reference for rose studies.

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.

RhRab5ip, a new interactor of RhPIP1;1, was involved in flower opening of cut rose during water deficit

Flower opening is a process primarily caused by water uptake-driven petal cell expansion. while which is easily affected by water deficit during transportation of cut flowers, resulting in abnormal flower opening. The knowledge of important players during this process remains limited. We previously reported that the aquaporin RhPIP1;1 plays an important role in ethylene-regulated petal cell expansion in rose flower. Here, we identified RhRab5ip as a new interactor of RhPIP1;1. RhRab5ip belongs to the Rab5-interacting protein (Rab5ip) family and may function in vesicle trafficking pathway. By using split ubiquitin yeast two-hybrid (SUY2H) system, bimolecular fluorescence complementation (BiFC) and subcellular colocalization we confirmed the existence of physical interaction between RhPIP1;1 and RhRab5ip in yeast and plant cell. The interaction of these two proteins happened at the small punctate structures in the cytoplasm. Expression of RhRab5ip in petals increased substantially at the initial stage of flower opening and maintained at high level until flower wilting. The transcripts of both RhRab5ip and RhPIP1;1 were greatly up-regulated by ABA and GA₃ treatments, while only RhPIP1;1 was down-regulated by ethylene. Moreover, both RhRab5ip and RhPIP1;1 were significantly induced by water deficit treatment after 12 h-treatment, when flowers started to wilt and showed neck bending. Taken together, these findings suggested that RhRab5ip might functionally coordinate with RhPIP1;1 in response to water deficit stress in rose flower, expanding our understanding of the possible involvement of Rab5ip protein in the regulatory network of flower opening during water deficit.

An Aux/IAA Family Member, RhIAA14, Involved in Ethylene-Inhibited Petal Expansion in Rose (Rosa hybrida)

Flower size, a primary agronomic trait in breeding of ornamental plants, is largely determined by petal expansion. Generally, ethylene acts as an inhibitor of petal expansion, but its effect is restricted by unknown developmental cues. In this study, we found that the critical node of ethylene-inhibited petal expansion is between stages 1 and 2 of rose flower opening. To uncover the underlying regulatory mechanism, we carried out a comparative RNA-seq analysis. Differentially expressed genes (DEGs) involved in auxin-signaling pathways were enriched. Therefore, we identified an auxin/indole-3-acetic acid (Aux/IAA) family gene, RhIAA14, whose expression was development-specifically repressed by ethylene. The silencing of RhIAA14 reduced cell expansion, resulting in diminished petal expansion and flower size. In addition, the expressions of cell-expansion-related genes, including RhXTH6, RhCesA2, RhPIP2;1, and RhEXPA8, were significantly downregulated following RhIAA14 silencing. Our results reveal an Aux/IAA that serves as a key player in orchestrating petal expansion and ultimately contributes to flower size, which provides new insights into ethylene-modulated flower opening and the function of the Aux/IAA transcription regulator.

PlMYB308 Regulates Flower Senescence by Modulating Ethylene Biosynthesis in Herbaceous Peony

Herbaceous peony is an important cut-flower plant cultivated worldwide, but its short vase life substantially restricts its economic value. It is well established that endogenous hormones regulate the senescence process, but their molecular mechanism in flower senescence remains unclear. Here, we isolated a MYB transcription factor gene, PlMYB308, from herbaceous peony flowers, based on transcriptome data. Quantitative real-time PCR analysis showed that PlMYB308 is strongly up-regulated in senescing petals, and its expression was induced by abscisic acid or ethylene and reduced by gibberellin in petals. Treatment with abscisic acid or ethylene accelerated herbaceous peony petal senescence, and gibberellin delayed the process. PlMYB308 silencing delayed peony flower senescence and dramatically increased gibberellin, but reduced ethylene and abscisic acid levels in petals. PlMYB308 ectopic overexpression in tobacco accelerated flower senescence and reduced gibberellin, but increased ethylene and abscisic acid accumulation. Correspondingly, five endogenous hormone biosynthetic genes showed variable expression levels in petals after PlMYB308 silencing or overexpression. A dual-luciferase assay and yeast one-hybrid analysis showed that PlMYB308 specifically binds the PlACO1 promoter. Moreover, treatment with ethylene and 1-MCP can accelerate PlMYB308 silencing-reduced senescence and delay PlMYB308- overexpression-induced senescence. We also found that PlACO1 silencing delayed senescence in herbaceous peony petals. Taken together, our results suggest that the PlMYB308-PlACO1 regulatory checkpoints positively mediate the production of ethylene, and thus contribute to senescence in herbaceous peony flowers.

A combined transcriptomic and proteomic analysis of chrysanthemum provides new insights into petal senescence

Numerous transcription factor genes and methylation-related genes were differentially expressed in senescent petals compared with control petals. Studying petal senescence is crucial for extending the postharvest longevity of cut flowers, but petal senescence remains relatively unexplored compared to well-studied leaf senescence. In this study, a combined transcriptomic and proteomic analysis of senescent (22 days after cutting) and control (0 day after cutting) petals was performed to investigate the molecular processes underlying petal senescence of chrysanthemum (Chrysanthemum morifolium Ramat.), an important cut flower crop worldwide. A total of 11,324 differentially expressed genes (DEGs), including 4888 up-regulated and 6436 down-regulated genes, and 403 differentially expressed proteins (DEPs), including 210 up-regulated and 193 down-regulated proteins, were identified at transcript and protein levels, respectively. A cross-comparison of transcriptomic and proteomic data identified 257 consistent DEGs/DEPs, including 122 up-regulated and 135 down-regulated DEGs/DEPs. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis showed that "cutin, suberine and wax biosynthesis" is a main pathway for both DEGs and DEPs, especially for down-regulated DEGs/DEPs. Functional analysis indicated that chrysanthemum genes mainly encoding putative cytochrome P450s, non-specific lipid-transfer proteins, subtilisin-like proteases, AAA-ATPases, proteins essential for cuticular wax biosynthesis, and proteins in hormone signal transduction or ubiquitination were differentially expressed at both transcript and protein levels. In addition, numerous transcription factor genes and methylation-related genes were also differentially expressed, inferring an involvement of transcriptional and epigenetic regulation in petal senescence. These results provide a valuable resource of studying chrysanthemum senescence and significant insights into petal senescence.

Characterization of wall-associated kinase/wall-associated kinase-like (WAK/WAKL) family in rose (Rosa chinensis) reveals the role of RcWAK4 in Botrytis resistance

BACKGROUND

Wall-associated kinase (WAK)/WAK-like (WAKL) is one of the subfamily of receptor like kinases (RLK). Although previous studies reported that WAK/WAKL played an important role in plant cell elongation, response to biotic and abiotic stresses, there are no systematic studies on RcWAK/RcWAKL in rose.

RESULTS

In this study, we identified a total of 68 RcWAK/RcWAKL gene family members within rose (Rosa chinensis) genome. The RcWAKs contained the extracellular galacturonan-binding domain and calcium-binding epidermal growth factor (EGF)-like domain, as well as an intracellular kinase domains. The RcWAKLs are missing either calcium-binding EGF-like domain or the galacturonan-binding domain in their extracellular region. The phylogenetic analysis showed the RcWAK/RcWAKL gene family has been divided into five groups, and these RcWAK/RcWAKL genes were unevenly distributed on the 7 chromosomes of rose. 12 of RcWAK/RcWAKL genes were significantly up-regulated by Botrytis cinerea-inoculated rose petals, where RcWAK4 was the most strongly expressed. Virus induced gene silencing of RcWAK4 increased the rose petal sensitivity to B. cinerea. The results indicated RcWAK4 is involved in the resistance of rose petal against B. cinerea.

CONCLUSION

Our study provides useful information to further investigate the function of the RcWAK/RcWAKL gene family and breeding research for resistance to B. cinerea in rose.

RhWRKY33 Positively Regulates Onset of Floral Senescence by Responding to Wounding- and Ethylene-Signaling in Rose Plants

Rose plants are one of the most important horticultural crops, whose commercial value mainly depends on long-distance transportation, and wounding and ethylene are the main factors leading to their quality decline and accelerated senescence in the process. However, underlying molecular mechanisms of crosstalk between wounding and ethylene in the regulation of flower senescence remain poorly understood. In relation to this, transcriptome analysis was performed on rose flowers subjected to various treatments, including control, wounding, ethylene, and wounding- and ethylene- (EW) dual treatment. A large number of differentially expressed genes (DEGs) were identified, ranging from 2,442 between the ethylene- and control-treated groups to 4,055 between the EW- and control-treated groups. Using weighted gene co-expression network analysis (WGCNA), we identified a hub gene RhWRKY33 (rchiobhmchr5g0071811), accumulated in the nucleus, where it may function as a transcription factor. Moreover, quantitative reverse transcription PCR (RT-qPCR) results showed that the expression of RhWRKY33 was higher in the wounding-, ethylene, and EW-treated petals than in the control-treated petals. We also functionally characterized the RhWRKY33 gene through virus-induced gene silencing (VIGS). The silencing of RhWRKY33 significantly delayed the senescence process in the different treatments (control, wounding, ethylene, and EW). Meanwhile, we found that the effect of RhWRKY33-silenced petals under ethylene and EW dual-treatment were stronger than those under wounding treatment in delaying the petal senescence process, implying that RhWRKY33 is closely involved with ethylene and wounding mediated petal senescence. Overall, the results indicate that RhWRKY33 positively regulates the onset of floral senescence mediated by both ethylene and wounding signaling, but relies heavily on ethylene signaling.

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.

The circadian-controlled PIF8-BBX28 module regulates petal senescence in rose flowers by governing mitochondrial ROS homeostasis at night

Reactive oxygen species (ROS) are unstable reactive molecules that are toxic to cells. Regulation of ROS homeostasis is crucial to protect cells from dysfunction, senescence, and death. In plant leaves, ROS are mainly generated from chloroplasts and are tightly temporally restricted by the circadian clock. However, little is known about how ROS homeostasis is regulated in nonphotosynthetic organs, such as petals. Here, we showed that hydrogen peroxide (H2O2) levels exhibit typical circadian rhythmicity in rose (Rosa hybrida) petals, consistent with the measured respiratory rate. RNA-seq and functional screening identified a B-box gene, RhBBX28, whose expression was associated with H2O2 rhythms. Silencing RhBBX28 accelerated flower senescence and promoted H2O2 accumulation at night in petals, while overexpression of RhBBX28 had the opposite effects. RhBBX28 influenced the expression of various genes related to respiratory metabolism, including the TCA cycle and glycolysis, and directly repressed the expression of SUCCINATE DEHYDROGENASE 1, which plays a central role in mitochondrial ROS (mtROS) homeostasis. We also found that PHYTOCHROME-INTERACTING FACTOR8 (RhPIF8) could activate RhBBX28 expression to control H2O2 levels in petals and thus flower senescence. Our results indicate that the circadian-controlled RhPIF8-RhBBX28 module is a critical player that controls flower senescence by governing mtROS homeostasis in rose.

Molecular understanding of postharvest flower opening and senescence

Flowers are key organs in many ornamental plants, and various phases of flower development impact their economic value. The final stage of petal development is associated with flower senescence, which is an irreversible process involving programmed cell death, and premature senescence of cut flowers often results in major losses in quality during postharvest handling. Flower opening and senescence are two sequential processes. As flowers open, the stamens are exposed to attract pollinators. Once pollination occurs, flower senescence is initiated. Both the opening and senescence processes are regulated by a range of endogenous phytohormones and environmental factors. Ethylene acts as a central regulator for the ethylene-sensitive flowers. Other phytohormones, including auxin, gibberellin, cytokinin, jasmonic acid and abscisic acid, are also involved in the control of petal expansion and senescence. Water status also directly influences postharvest flower opening, while pollination is a key event in initiating the onset flower senescence. Here, we review the current understanding of flower opening and senescence, and propose future research directions, such as the study of interactions between hormonal and environmental signals, the application of new technology, and interdisciplinary research.

Regulation of Botrytis cinerea Infection and Gene Expression in Cut Roses by Using Nano Silver and Salicylic Acid

Botrytis cinerea (B. cinerea) is one of the necrotrophic pathogens resulting in the heaviest commercial losses in cut rose flowers, and the severity of gray mold disease partly depends on the presence of ethylene during the storage and transport. The effectiveness of nano silver (NS) and salicylic acid (SA) was assessed as a novel control agent in protecting the cut rose flowers against B. cinerea infection and ethylene damages. The efficacy of NS and SA was compared with an inoculated control (CON). A non-treated control (NT) was also used to evaluate the natural infection process. The results indicated that pretreatment with 20 mg L-1 NS significantly reduced B. cinerea growth in rose petals during vase periods. NS effectively suppressed the mRNA levels of ethylene biosynthesis genes (RhACS2, RhACS4, and RhACO1) and the reduction in expression levels of ethylene receptor genes (RhETR1, RhETR2, and RhETR5) and the downstream regulator RhCTR2 in rose petals after B. cinerea inoculation. NS application also decreased the expression of the B. cinerea snod-prot-like 1 (Bcspl1) gene which acts as the virulence factor in cut roses. In NS flowers, the maximum quantum yield of PSII (Fv/Fm) value was higher and the leaf temperature was lower on day 1, suggesting that these factors can be used for detecting B. cinerea infection and water stress in cut rose flowers. Furthermore, NS improved water relations and extended the vase life of cut rose flowers by 3.3 d, compared with that of NT flowers. In contrast, SA had no inhibitive effects on both B. cinerea growth and ethylene response in cut roses. The findings from the present study highlight NS as a promising new candidate for preventing B. cinerea infection and ethylene damages and for improving the postharvest quality of cut roses exported overseas.

Ethylene-regulated asymmetric growth of the petal base promotes flower opening in rose (Rosa hybrida)

Flowers are the core reproductive structures and key distinguishing features of angiosperms. Flower opening to expose stamens and gynoecia is important in cases where pollinators much be attracted to promote cross-pollination, which can enhance reproductive success and species preservation. The floral opening process is accompanied by the coordinated movement of various floral organs, particularly petals. However, the mechanisms underlying petal movement and flower opening are not well understood. Here, we integrated anatomical, physiological, and molecular approaches to determine the petal movement regulatory network using rose (Rosa hybrida) as a model. We found that PETAL MOVEMENT-RELATED PROTEIN1 (RhPMP1), a homeodomain transcription factor (TF) gene, is a direct target of ETHYLENE INSENSITIVE3, a TF that functions downstream of ethylene signaling. RhPMP1 expression was upregulated by ethylene and specifically activated endoreduplication of parenchyma cells on the adaxial side of the petal (ADSP) base by inducing the expression of RhAPC3b, a gene encoding the core subunit of the Anaphase-Promoting Complex. Cell expansion of the parenchyma on the ADSP base was subsequently enhanced, thus resulting in asymmetric growth of the petal base, leading to the typical epinastic movement of petals and flower opening. These findings provide insights into the pathway regulating petal movement and associated flower-opening mechanisms.�.

Ethylene biosynthesis and response factors are differentially modulated during the interaction of peach petals with Monilinia laxa or Monilinia fructicola

Monilinia spp. may infect stone fruit at any growth stage, although susceptibility to brown rot depends on both host properties and climatological conditions. This said, no studies deciphering the host response in the interaction between peach blossoms and Monilinia spp. are yet available. This study presents an in-depth characterization of the role of ethylene in the interaction of 'Merrill O'Henry' peach petals (Prunus persica (L.) Batch) with Monilinia laxa and M. fructicola. We investigated the physiological responses of the host and the fungi to the application of ethylene and 1-methylcyclopropene (1-MCP) as well as the molecular patterns associated with the biosynthetic and ethylene-dependent responses during the interaction of both Monilinia species with the host. The incidence of both species was differentially affected by 1-MCP and ethylene; M. laxa was favoured by the enhanced host ethylene production associated with the treatments whereas M. fructicola reduced its infection capacity. Such differences were host-dependent as treatments did not affect growth or colony morphology of Monilinia spp. Besides, host ethylene production was altered in M. laxa inoculated petals, either by the fungus or the host itself. Molecular analysis revealed some important ERFs that could be involved in the different ability of both species to activate a cascade response of peach petals against these pathogens.

The RhHB1/RhLOX4 module affects the dehydration tolerance of rose flowers (Rosa hybrida) by fine-tuning jasmonic acid levels

Phytohormones are key factors in plant responsiveness to abiotic and biotic stresses, and maintaining hormone homeostasis is critically important during stress responses. Cut rose (Rosa hybrida) flowers experience dehydration stress during postharvest handling, and jasmonic acid (JA) levels change as a result of this stress. However, how JA is involved in dehydration tolerance remains unclear. We investigated the functions of the JA- and dehydration-induced RhHB1 gene, which encodes a homeodomain-leucine zipper I γ-clade transcription factor, in rose flowers. Silencing RhHB1 decreased petal dehydration tolerance and resulted in a persistent increase in JA-Ile content and reduced dehydration tolerance. An elevated JA-Ile level had a detrimental effect on rose petal dehydration tolerance. RhHB1 was shown to lower the transient induction of JA-Ile accumulation in response to dehydration. In addition to transcriptomic data, we obtained evidence that RhHB1 suppresses the expression of the lipoxygenase 4 (RhLOX4) gene by directly binding to its promoter both in vivo and in vitro. We propose that increased JA-Ile levels weaken the capacity for osmotic adjustment in petal cells, resulting in reduced dehydration tolerance. In conclusion, a JA feedback loop mediated by an RhHB1/RhLOX4 regulatory module provides dehydration tolerance by fine-tuning bioactive JA levels in dehydrated flowers.

Integrating physiological and metabolites analysis to identify ethylene involvement in petal senescence in Tulipa gesneriana

Flower senescence is classified into ethylene-dependent and ethylene-independent manners and determines the flower longevity which is valuable for ornamental plants. However, the manner of petal senescence in tulip is still less defined. In this study, we characterized the physiological indexes in the process of petal senescence, as well as metabolic and ethylene responses in tulip cultivar 'American Dream', and further identified the role of ethylene biosynthesis genes TgACS by transgenic and transient assays. Primary metabolites profiling revealed that sugars, amino acids and organic acids preferentially accumulated in senescent petals. Additionally, senescence-associated genes were identified and significantly up-regulated, coupled with increased ROS contents, rapid water loss and accelerated cell membrane breakdown. Moreover, ethylene production was stimulated as evidenced by increasing in ACS activity and ethylene biosynthesis-related genes expression. Exogenous treatment of cutting flowers with 1-MCP or ethephon resulted in delayed or enhanced petal senescence, respectively. Transient down-regulation of TgACS by VIGS assay in tulip petals delayed senescence, while over-expressed TgACS1 in tobacco promoted leaf senescence. Taken together, this study provides evidences to certify ethylene roles and TgACS functions during flower senescence in tulip.

Selenium-Ethylene Interplay in Postharvest Life of Cut Flowers

Selenium (Se) is considered a beneficial element in higher plants when provided at low concentrations. Recently, studies have unveiled the interactions between Se and ethylene metabolism throughout plant growth and development. However, despite the evidence that Se may provide longer shelf life in ethylene-sensitive flowers, its primary action on ethylene biosynthesis and cause-effect responses are still understated. In the present review, we discuss the likely action of Se on ethylene biosynthesis and its consequence on postharvest physiology of cut flowers. By combining Se chemical properties with a dissection of ethylene metabolism, we further highlighted both the potential use of Se solutions and their downstream responses. We believe that this report will provide the foundation for the hypothesis that Se plays a key role in the postharvest longevity of ethylene-sensitive flowers.

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.

RhMYB108, an R2R3-MYB transcription factor, is involved in ethylene- and JA-induced petal senescence in rose plants

Rose (Rosa hybrida) plants are major ornamental species worldwide, and their commercial value greatly depends on their open flowers, as both the quality of fully open petals and long vase life are important. Petal senescence can be started and accelerated by various hormone signals, and ethylene is considered an accelerator of petal senescence in rose. To date, however, the underlying mechanism of signaling crosstalk between ethylene and other hormones such as JA in petal senescence remains largely unknown. Here, we isolated RhMYB108, an R2R3-MYB transcription factor, which is highly expressed in senescing petals as well as in petals treated with exogenous ethylene and JA. Applications of exogenous ethylene and JA markedly accelerated petal senescence, while the process was delayed in response to applications of 1-MCP, an ethylene action inhibitor. In addition, silencing of RhMYB108 alter the expression of SAGs such as RhNAC029, RhNAC053, RhNAC092, RhSAG12, and RhSAG113, and finally block ethylene- and JA-induced petal senescence. Furthermore, RhMYB108 was identified to target the promoters of RhNAC053, RhNAC092, and RhSAG113. Our results reveal a model in which RhMYB108 functions as a receptor of ethylene and JA signals to modulate the onset of petal senescence by targeting and enhancing senescence-associated gene expression.

Differential and reciprocal regulation of ethylene pathway genes regulates petal abscission in fragrant and non-fragrant roses

The fragrant rose, Rosa bourboniana, is highly sensitive to ethylene and shows rapid petal abscission (within 16-18 h) while the non-fragrant hybrid rose, R. hybrida, shows delayed abscission (50-52 h) due to reduced ethylene sensitivity. To understand the molecular basis governing these differences, all components of the ethylene pathway (biosynthesis/ receptor/signalling) were studied for expression during abscission. Transcript accumulation of most ethylene biosynthesis genes (ACS/ACO families) increased rapidly in petal abscission zones of R. bourboniana within 4-8 h of ethylene treatment. The expression of most receptor and signalling genes encoding CTRs, EIN2 and EIN3/EIL homologues also followed similar kinetics. Under natural field conditions where abscission takes longer, there was a temporal delay in transcript accumulation of most ethylene pathway genes while some biosynthesis genes (showing reduced ethylene sensitivity) were more strongly up-regulated by abscission cues. In contrast, in R. hybrida where even ethylene-induced abscission is considerably delayed, transcript accumulation of most ethylene biosynthesis and signalling genes was, surprisingly, reduced by ethylene and showed an opposite regulation compared to R. bourboniana. The results suggest that differential and reciprocal regulation of ethylene pathway is one of the major reasons for differences in petal abscission and vase-life between Rosa bourboniana and R. hybrida.

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.

Petal senescence: a hormone view

Flowers are highly complex organs that have evolved to enhance the reproductive success of angiosperms. As a key component of flowers, petals play a vital role in attracting pollinators and ensuring successful pollination. Having fulfilled this function, petals senesce through a process that involves many physiological and biochemical changes that also occur during leaf senescence. However, petal senescence is distinct, due to the abundance of secondary metabolites in petals and the fact that petal senescence is irreversible. Various phytohormones are involved in regulating petal senescence, and are thought to act both synergistically and antagonistically. In this regard, there appears to be developmental point during which such regulatory signals are sensed and senescence is initiated. Here, we review current understanding of petal senescence, and discuss associated regulatory mechanisms involving hormone interactions and epigenetic regulation.

A RhABF2/Ferritin module affects rose (Rosa hybrida) petal dehydration tolerance and senescence by modulating iron levels

Plants often develop the capacity to tolerate moderate and reversible environmental stresses, such as drought, and to re-establish normal development once the stress has been removed. An example of this phenomenon is provided by cut rose (Rosa hybrida) flowers, which experience typical reversible dehydration stresses during post-harvest handling after harvesting at the bud stages. The molecular mechanisms involved in rose flower dehydration tolerance are not known, however. Here, we characterized a dehydration- and abscisic acid (ABA)-induced ferritin gene (RhFer1). Dehydration-induced free ferrous iron (Fe²⁺ ) is preferentially sequestered by RhFer1 and not transported outside of the petal cells, to restrict oxidative stresses during dehydration. Free Fe²⁺ accumulation resulted in more serious oxidative stresses and the induction of genes encoding antioxidant enzyme in RhFer1-silenced petals, and poorer dehydration tolerance was observed compared with tobacco rattle virus (TRV) controls. We also determined that RhABF2, an AREB/ABF transcription factor involved in the ABA signaling pathway, can activate RhFer1 expression by directly binding to its promoter. The silencing of RhABF2 decreased dehydration tolerance and disrupted Fe homeostasis in rose petals during dehydration, as did the silencing of RhFer1. Although both RhFer1 and Fe transporter genes are induced during flower natural senescence in plants, the silencing of RhABF2 or RhFer1 accelerates the petal senescence processes. These results suggest that the regulatory module RhABF2/RhFer1 contributes to the maintenance of Fe levels and enhances dehydration tolerance through the action of RhFer1 locally sequestering free Fe²⁺ under dehydration conditions, and plays synergistic roles with transporter genes during flower senescence.

RhMKK9, a rose MAP KINASE KINASE gene, is involved in rehydration-triggered ethylene production in rose gynoecia

BACKGROUND

Flower opening is an important process in the life cycle of flowering plants and is influenced by various endogenous and environmental factors. Our previous work demonstrated that rose (Rosa hybrida) flowers are highly sensitive to dehydration during flower opening and the water recovery process after dehydration induced ethylene production rapidly in flower gynoecia. In addition, this temporal- and spatial-specific ethylene production is attributed to a transient but robust activation of the rose MAP KINASE6-ACC SYNTHASE1 (RhMPK6-RhACS1) cascade in gynoecia. However, the upstream component of RhMPK6-RhACS1 is unknown, although RhMKK9 (MAP KINASE KINASE9), a rose homologue of Arabidopsis MKK9, could activate RhMPK6 in vitro. In this study, we monitored RhMKK2/4/5/9 expression, the potential upstream kinase to RhMPK6, in rose gynoecia during dehydration and rehydration.

RESULTS

We found only RhMKK9 was rapidly and strongly induced by rehydration. Silencing of RhMKK9 significantly decreased rehydration-triggered ethylene production. Consistently, the expression of several ethylene-responsive genes was down regulated in the petals of RhMKK9-silenced flowers. Moreover, we detected the DNA methylation level in the promoter and gene body of RhMKK9 by Chop-PCR. The results showed that rehydration specifically elevated the DNA methylation level on the RhMKK9 gene body, whereas it resulted in hypomethylation in its promoter.

CONCLUSIONS

Our results showed that RhMKK9 possibly acts as the upstream component of the RhMKK9-RhMPK6-RhACS1 cascade and is responsible for water recovery-triggered ethylene production in rose gynoecia, and epigenetic DNA methylation is involved in the regulation of RhMKK9 expression by rehydration.

Comparative RNA-seq analysis of transcriptome dynamics during petal development in Rosa chinensis

The developmental process that produces the ornate petals of the China rose (Rosa chinensis) is complex and is thought to depend on the balanced expression of a functionally diverse array of genes; however, the molecular basis of rose petal development is largely unknown. Here, petal growth of the R. chinensis cultivar 'Old Blush' was divided into four developmental stages, and RNA-seq technology was used to analyse the dynamic changes in transcription that occur as development progresses. In total, 598 million clean reads and 61,456 successfully annotated unigenes were obtained. Differentially expressed gene (DEG) analysis comparing the transcriptomes of the developmental stages resulted in the identification of several potential candidate genes involved in petal development. DEGs involved in anthocyanin biosynthesis, petal expansion, and phytohormone pathways were considered in depth, in addition to several candidate transcription factors. These results lay a foundation for future studies on the regulatory mechanisms underlying rose petal development and may be used in molecular breeding programs aimed at generating ornamental rose lines with desirable traits.

Low temperature-induced DNA hypermethylation attenuates expression of RhAG, an AGAMOUS homolog, and increases petal number in rose (Rosa hybrida)

BACKGROUND

Flower development is central to angiosperm reproduction and is regulated by a broad range of endogenous and exogenous stimuli. It has been well documented that ambient temperature plays a key role in controlling flowering time; however, the mechanisms by which temperature regulates floral organ differentiation remain largely unknown.

RESULTS

In this study, we show that low temperature treatment significantly increases petal number in rose (Rosa hybrida) through the promotion of stamen petaloidy. Quantitative RT-PCR analysis revealed that the expression pattern of RhAG, a rose homolog of the Arabidopsis thaliana AGAMOUS C-function gene, is associated with low temperature regulated flower development. Silencing of RhAG mimicked the impact of low temperature treatments on petal development by significantly increasing petal number through an increased production of petaloid stamens. In situ hybridization studies further revealed that low temperature restricts its spatial expression area. Analysis of DNA methylation level showed that low temperature treatment enhances the methylation level of the RhAG promoter, and a specific promoter region that was hypermethylated at CHH loci under low temperature conditions, was identified by bisulfite sequencing. This suggests that epigenetic DNA methylation contributes to the ambient temperature modulation of RhAG expression.

DISCUSSION

Our results provide highlights in the role of RhAG gene in petal number determination and add a new layer of complexity in the regulation of floral organ development.

CONCLUSIONS

We propose that RhAG plays an essential role in rose flower patterning by regulating petal development, and that low temperatures increase petal number, at least in part, by suppressing RhAG expression via enhancing DNA CHH hypermethylation of the RhAG promoter.

Responses of rose RhACS1 and RhACS2 promoters to abiotic stresses in transgenic Arabidopsis thaliana

Promoter activities of RhACS1 and RhACS2 , two rose genes involved in ethylene biosynthesis, are highly sensitive to various abiotic stresses in an organ-specific manner. Our previous studies indicated that two rose (Rosa hybrida) 1-aminocyclopropane-1-carboxylic acid synthase genes, RhACS1 and RhACS2, play a role in dehydration-induced ethylene production and inhibition of cell expansion in rose petals. Here, both RhACS1 and RhACS2 promoters were analyzed using histochemical staining and glucuronidase synthase (GUS) gene reporter activity assays following their introduction into transgenic Arabidopsis thaliana plants. It was found that the promoter activities of both genes were strong throughout the course of development from young seedlings to mature flowering plants in various organs, including hypocotyls, cotyledons, leaves, roots and lateral roots. RhACS1 promoter activity was induced by drought in both rosette leaves and roots of transgenic A. thaliana lines, but was reduced following a re-hydration treatment. In contrast, RhACS2 promoter activity was decreased by drought in rosette leaves, while its response pattern was similar to that of RhACS1 in roots. A mannitol treatment induced the activity of both the RhACS1 and RhACS2 promoters, indicating that both genes are also regulated by osmotic stress. In addition, RhACS2 appeared to be abscisic acid (ABA)-inducible, while RhACS1 was less sensitive to ABA. Finally, four truncated sequences of the RhACS1 promoter were generated and GUS activity assays demonstrated that deleting a 327 bp region between bp 862 and -535 resulted in a substantial decrease of the promoter activity. Taken together, our results suggest that the RhACS1 and RhACS2 promoters respond to abiotic stresses in a developmentally regulated and spatially specific manner.

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

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

RhHB1 mediates the antagonism of gibberellins to ABA and ethylene during rose (Rosa hybrida) petal senescence

Rose (Rosa hybrida) is one of the most important ornamental plants worldwide; however, senescence of its petals terminates the ornamental value of the flower, resulting in major economic loss. It is known that the hormones abscisic acid (ABA) and ethylene promote petal senescence, while gibberellins (GAs) delay the process. However, the molecular mechanisms underlying the antagonistic effects amongst plant hormones during petal senescence are still unclear. Here we isolated RhHB1, a homeodomain-leucine zipper I transcription factor gene, from rose flowers. Quantitative RT-PCR and GUS reporter analyses showed that RhHB1 was strongly expressed in senescing petals, and its expression was induced by ABA or ethylene in petals. ABA or ethylene treatment clearly accelerated rose petal senescence, while application of the gibberellin GA3 delayed the process. However, silencing of RhHB1 delayed the ABA- or ethylene-mediated senescence, and resulted in higher petal anthocyanin levels and lower expression of RhSAG12. Moreover, treatment with paclobutrazol, an inhibitor of GA biosynthesis, repressed these delays. In addition, silencing of RhHB1 blocked the ABA- or ethylene-induced reduction in expression of the GA20 oxidase encoded by RhGA20ox1, a gene in the GA biosynthetic pathway. Furthermore, RhHB1 directly binds to the RhGA20ox1 promoter, and silencing of RhGA20ox1 promoted petal senescence. Eight senescence-related genes showed substantial differences in expression in petals after treatment with GA3 or paclobutrazol. These results suggest that RhHB1 mediates the antagonistic effect of GAs on ABA and ethylene during rose petal senescence, and that the promotion of petal senescence by ABA or ethylene operates through an RhHB1-RhGA20ox1 regulatory checkpoint.

RhNAC3, a stress-associated NAC transcription factor, has a role in dehydration tolerance through regulating osmotic stress-related genes in rose petals

Petal cell expansion depends on cell wall metabolism, changes in cell turgor pressure and restructuring of the cytoskeleton, and recovery ability of petal cell expansion is defined as an indicator of dehydration tolerance in flowers. We previously reported that RhNAC2, a development-related NAC domain transcription factor, confers dehydration tolerance through regulating cell wall-related genes in rose petals. Here, we identify RhNAC3, a novel rose SNAC gene, and its expression in petals induced by dehydration, wounding, exogenous ethylene and abscisic acid (ABA). Expression studies in Arabidopsis protoplasts and yeast show that RhNAC3 has transactivation activity along its full length and in the carboxyl-terminal domain. Silencing RhNAC3 in rose petals by virus-induced gene silencing (VIGS) significantly decreased the cell expansion of rose petals under rehydration conditions. In total, 24 of 27 osmotic stress-related genes were down-regulated in RhNAC3-silenced rose petals, while only 4 of 22 cell expansion-related genes were down-regulated. Overexpression of RhNAC3 in Arabidopsis gave improved drought tolerance, with lower water loss of leaves in transgenic plants. Arabidopsis ATH1 microarray analysis showed that RhNAC3 regulated the expression of stress-responsive genes in overexpressing lines, and further analysis revealed that most of the RhNAC3-up-regulated genes were involved in the response to osmotic stress. Comparative analysis revealed that different transcription regulation existed between RhNAC3 and RhNAC2. Taken together, these data indicate that RhNAC3, as a positive regulator, confers dehydration tolerance of rose petals mainly through regulating osmotic adjustment-associated genes.

Involvement of rose aquaporin RhPIP1;1 in ethylene-regulated petal expansion through interaction with RhPIP2;1

Aquaporins (AQPs) are multifunctional membrane channels and facilitate the transport of water across plant cell membranes. Among the plant AQPs, plasma membrane intrinsic proteins (PIPs), which cluster in two phylogenetic groups (PIP1 and PIP2), play a key role in plant growth. Our previous work has indicated that RhPIP2;1, a member of PIP2, is involved in ethylene-regulated cell expansion of rose petals. However, whether PIP1s also play a role in petal expansion is still unclear. Here, we identified RhPIP1;1, a PIP1 subfamily member, from 18 PIPs assemble transcripts in rose microarray database responsive to ethylene. RhPIP1;1 was rapidly and significantly down-regulated by ethylene treatment. RhETRs-silencing also clearly decreased the expression of RhPIP1;1 in rose petals. The activity of the RhPIP1;1 promoter was repressed by ethylene in rosettes and roots of Arabidopsis. RhPIP1;1 is mainly localized on endoplasmic reticulum and plasma membrane. We demonstrated that RhPIP1;1-silencing significantly inhibited the expansion of petals with decreased petal size and cell area, as well as reduced fresh weight when compared to controls. Expression of RhPIP1;1 in Xenopus oocytes indicated that RhPIP1;1 was inactive in terms of water transport, while coexpression of RhPIP1;1 with the functional RhPIP2;1 led to a significant increase in plasma membrane permeability. Yeast growth, β-Galactosidase activity, bimolecular fluorescence complementation, and colocalization assay proved existence of the interaction between RhPIP1;1 and RhPIP2;1. We argue that RhPIP1;1 plays an important role in ethylene-regulated petal cell expansion, at least partially through the interaction with RhPIP2;1.

Integrative analysis of miRNA and mRNA profiles in response to ethylene in rose petals during flower opening

MicroRNAs play an important role in plant development and plant responses to various biotic and abiotic stimuli. As one of the most important ornamental crops, rose (Rosa hybrida) possesses several specific morphological and physiological features, including recurrent flowering, highly divergent flower shapes, colors and volatiles. Ethylene plays an important role in regulating petal cell expansion during rose flower opening. Here, we report the population and expression profiles of miRNAs in rose petals during flower opening and in response to ethylene based on high throughput sequencing. We identified a total of 33 conserved miRNAs, as well as 47 putative novel miRNAs were identified from rose petals. The conserved and novel targets to those miRNAs were predicted using the rose floral transcriptome database. Expression profiling revealed that expression of 28 known (84.8% of known miRNAs) and 39 novel (83.0% of novel miRNAs) miRNAs was substantially changed in rose petals during the earlier opening period. We also found that 28 known and 22 novel miRNAs showed expression changes in response to ethylene treatment. Furthermore, we performed integrative analysis of expression profiles of miRNAs and their targets. We found that ethylene-caused expression changes of five miRNAs (miR156, miR164, miR166, miR5139 and rhy-miRC1) were inversely correlated to those of their seven target genes. These results indicate that these miRNA/target modules might be regulated by ethylene and were involved in ethylene-regulated petal growth.

An organ-specific role for ethylene in rose petal expansion during dehydration and rehydration

Dehydration is a major factor resulting in huge loss from cut flowers during transportation. In the present study, dehydration inhibited petal cell expansion and resulted in irregular flowers in cut roses, mimicking ethylene-treated flowers. Among the five floral organs, dehydration substantially elevated ethylene production in the sepals, whilst rehydration caused rapid and elevated ethylene levels in the gynoecia and sepals. Among the five ethylene biosynthetic enzyme genes (RhACS1-5), expression of RhACS1 and RhACS2 was induced by dehydration and rehydration in the two floral organs. Silencing both RhACS1 and RhACS2 significantly suppressed dehydration- and rehydration-induced ethylene in the sepals and gynoecia. This weakened the inhibitory effect of dehydration on petal cell expansion. β-glucuronidase activity driven by both the RhACS1 and RhACS2 promoters was dramatically induced in the sepals, pistil, and stamens, but not in the petals of transgenic Arabidopsis. This further supports the organ-specific induction of these two genes. Among the five rose ethylene receptor genes (RhETR1-5), expression of RhETR3 was predominantly induced by dehydration and rehydration in the petals. RhETR3 silencing clearly aggravated the inhibitory effect of dehydration on petal cell expansion. However, no significant difference in the effect between RhETR3-silenced flowers and RhETR-genes-silenced flowers was observed. Furthermore, RhETR-genes silencing extensively altered the expression of 21 cell expansion-related downstream genes in response to ethylene. These results suggest that induction of ethylene biosynthesis by dehydration proceeds in an organ-specific manner, indicating that ethylene can function as a mediator in dehydration-caused inhibition of cell expansion in rose petals.

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

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

Regulation of the rose Rh-PIP2;1 promoter by hormones and abiotic stresses in Arabidopsis

Our previous work has indicated that an ethylene-responsive aquaporin gene, Rh-PIP2;1, played an important role in the epidermal cell expansion of rose petals. In this work, we isolated an 896 bp promoter sequence of the Rh-PIP2;1 and found that the promoter was rare in plants, occurring with an Inr motif, but without a TATA box. In transgenic Arabidopsis harboring the Rh-PIP2;1 promoter::GUS construct, the activity of Rh-PIP2;1 promoter was found to be developmental-dependent in almost all of the tested organs, and was particularly active in organs that were rapidly expanding, and in tissues with high water flux capacity. Moreover, the promoter activity was inhibited by ACC, ABA, NaCl, and cold in the roots of 3 or 6-day-old plants, and was increased by GA(3) and mannitol in the rosettes of 9 or 12-day-old plants. Deleting the fragment from -886 to -828 resulted in nearly complete disappearance of the promoter activity in roots, and a substantial decrease in the leaves, hypocotyls and floral organs. Taken together, our results indicated that the Rh-PIP2;1 promoter responded to hormones and abiotic stresses in a developmental- and spatial-dependent manner, and the -886 to -828 region was crucial for the activity of the Rh-PIP2;1 promoter.