Investigation of Petal Senescence by TRV-Mediated Virus-Induced Gene Silencing in Rose

An insertion of transposon in DcNAP inverted its function in the ethylene pathway to delay petal senescence in carnation (Dianthus caryophyllus L.)

Petal senescence is the final stage of flower development. Transcriptional regulation plays key roles in this process. However, whether and how post-transcriptional regulation involved is still largely unknown. Here, we identified an ethylene-induced NAC family transcription factor DcNAP in carnation (Dianthus caryophyllus L.). One allele, DcNAP-dTdic1, has an insertion of a dTdic1 transposon in its second exon. The dTdic1 transposon disrupts the structure of DcNAP and causes alternative splicing, which transcribes multiple domain-deleted variants (DcNAP2 and others). Conversely, the wild type allele DcNAP transcribes DcNAP1 encoding an intact NAC domain. Silencing DcNAP1 delays and overexpressing DcNAP1 accelerates petal senescence in carnation, while silencing and overexpressing DcNAP2 have the opposite effects, respectively. Further, DcNAP2 could interact with DcNAP1 and interfere the binding and activation activity of DcNAP1 to the promoters of its downstream target ethylene biosynthesis genes DcACS1 and DcACO1. Lastly, ethylene signalling core transcriptional factor DcEIL3-1 can activate the expression of DcNAP1 and DcNAP2 in the same way by binding their promoters. In summary, we discovered a novel mechanism by which DcNAP regulates carnation petal senescence at the post-transcriptional level. It may also provide a useful strategy to manipulate the NAC domains of NAC transcription factors for crop genetic improvement.

Establishment of virus-induced gene silencing (VIGS) system in Luffa acutangula using Phytoene desaturase (PDS) and tendril synthesis related gene (TEN)

BACKGROUND

Virus-induced gene silencing (VIGS) is a reverse genetics technology that can efficiently and rapidly identify plant gene functions. Although a variety of VIGS vectors have been successfully used in plants, only a few reports on VIGS technology in Luffa exist.

RESULTS

In the present study, a new cucumber green mottle mosaic virus (CGMMV)-based VIGS vector, pV190, was applied to establish the CGMMV-VIGS to investigate the feasibility of the silencing system for Luffa. Phytoene desaturase (PDS) gene was initially selected as a VIGS marker gene to construct a recombinant vector. Plants infected with Agrobacterium harboring pV190-PDS successfully induced effective silencing in Luffa, and an effective gene silencing phenotype with obvious photobleaching was observed. To further validate the efficiency, we selected TEN for gene-silencing, which encodes a CYC/TB1-like transcription factor and is involved in tendril development. Luffa plants inoculated with the pV190-TEN exhibited shorter tendril length and nodal positions where tendrils appear are higher compared to those of non-inoculated plants. RT-qPCR showed that the expression levels of PDS and TEN were significantly reduced in the CGMMV-VIGS plants. Moreover, we evaluated the CGMMV-VIGS efficiency in three cucurbits, including cucumber, ridge gourd, and bottle gourd.

CONCLUSION

We successfully established a CGMMV-based VIGS system on ridge gourd and used marker genes to identify the feasibility of the silencing system in Luffa leaves and stems.

DcWRKY33 promotes petal senescence in carnation (Dianthus caryophyllus L.) by activating genes involved in the biosynthesis of ethylene and abscisic acid and accumulation of reactive oxygen species

Carnation (Dianthus caryophyllus L.) is one of the most famous and ethylene-sensitive cut flowers worldwide, but how ethylene interacts with other plant hormones and factors to regulate petal senescence in carnation is largely unknown. Here we found that a gene encoding WRKY family transcription factor, DcWRKY33, was significantly upregulated upon ethylene treatment. Silencing and overexpression of DcWRKY33 could delay and accelerate the senescence of carnation petals, respectively. Abscisic acid (ABA) and H₂ O₂ treatments could also accelerate the senescence of carnation petals by inducing the expression of DcWRKY33. Further, DcWRKY33 can bind directly to the promoters of ethylene biosynthesis genes (DcACS1 and DcACO1), ABA biosynthesis genes (DcNCED2 and DcNCED5), and the reactive oxygen species (ROS) generation gene DcRBOHB to activate their expression. Lastly, relationships are existed between ethylene, ABA and ROS. This study elucidated that DcWRKY33 promotes petal senescence by activating genes involved in the biosynthesis of ethylene and ABA and accumulation of ROS in carnation, supporting the development of new strategies to prolong the vase life of cut carnation.

Integrated analysis of miRNAome transcriptome and degradome reveals miRNA-target modules governing floral florescence development and senescence across early- and late-flowering genotypes in tree peony

As a candidate national flower of China, tree peony has extremely high ornamental, medicinal and oil value. However, the short florescence and rarity of early-flowering and late-flowering varieties restrict further improvement of the economic value of tree peony. Specific miRNAs and their target genes engaged in tree peony floral florescence, development and senescence remain unknown. This report presents the integrated analysis of the miRNAome, transcriptome and degradome of tree peony petals collected from blooming, initial flowering, full blooming and decay stages in early-flowering variety Paeonia ostii 'Fengdan', an early-flowering mutant line of Paeonia ostii 'Fengdan' and late-flowering variety Paeonia suffruticosa 'Lianhe'. Transcriptome analysis revealed a transcript ('psu.G.00014095') which was annotated as a xyloglucan endotransglycosylase/hydrolase precursor XTH-25 and found to be differentially expressed across flower developmental stages in Paeonia ostii 'Fengdan' and Paeonia suffruticosa 'Lianhe'. The miRNA-mRNA modules were presented significant enrichment in various pathways such as plant hormone signal transduction, indole alkaloid biosynthesis, arachidonic acid metabolism, folate biosynthesis, fatty acid elongation, and the MAPK signaling pathway. Multiple miRNA-mRNA-TF modules demonstrated the potential functions of MYB-related, bHLH, Trihelix, NAC, GRAS and HD-ZIP TF families in floral florescence, development, and senescence of tree peony. Comparative spatio-temporal expression investigation of eight floral-favored miRNA-target modules suggested that transcript 'psu.T.00024044' and microRNA mtr-miR166g-5p are involved in the floral florescence, development and senescence associated agronomic traits of tree peony. The results might accelerate the understanding of the potential regulation mechanism in regards to floral florescence, development and abscission, and supply guidance for tree peony breeding of varieties with later and longer florescence characteristics.

The transcription factors DcHB30 and DcWRKY75 antagonistically regulate ethylene-induced petal senescence in carnation (Dianthus caryophyllus)

Although numerous transcription factors with antagonistic activities have been shown to contribute to growth and development, whether and how they regulate senescence in plants is largely unknown. In this study, we investigated the role of antagonistic transcription factors in petal senescence in carnation (Dianthus caryophyllus), one of the most common types of ethylene-sensitive cut flowers produced worldwide. We identified DcHB30 that encodes a ZF-HD transcription factor that is down-regulated in ethylene-treated petal transcriptomes. We found that silencing DcHB30 accelerated ethylene-induced petal senescence and that DcHB30 physically interacts with DcWRKY75, a positive regulator of ethylene-induced petal senescence. Phenotypic characterization and molecular evidence indicated that DcHB30 and DcWRKY75 competitively regulate the expression of their co-targeted genes DcACS1, DcACO1, DcSAG12, and DcSAG29 by reciprocally inhibiting the DNA-binding activity of each other on the gene promoters. This transcriptional regulation mechanism demonstrates that these transcription factors serve as positive and negative regulators in ethylene-induced petal senescence in carnation. Thus, our study provides insights into how antagonizing transcription factors regulate plant senescence.

Regulation of cytokinin biosynthesis using PtRD26pro -IPT module improves drought tolerance through PtARR10-PtYUC4/5-mediated reactive oxygen species removal in Populus

Drought is a critical environmental factor which constrains plant survival and growth. Genetic engineering provides a credible strategy to improve drought tolerance of plants. Here, we generated transgenic poplar lines expressing the isopentenyl transferase gene (IPT) under the driver of PtRD26 promoter (PtRD26_pro -IPT). PtRD26 is a senescence and drought-inducible NAC transcription factor. PtRD26_pro -IPT plants displayed multiple phenotypes, including improved growth and drought tolerance. Transcriptome analysis revealed that auxin biosynthesis pathway was activated in the PtRD26_pro -IPT plants, leading to an increase in auxin contents. Biochemical analysis revealed that ARABIDOPSIS RESPONSE REGULATOR10 (PtARR10), one of the type-B ARR transcription factors in the cytokinin pathway, was induced in PtRD26_pro -IPT plants and directly regulated the transcripts of YUCCA4 (PtYUC4) and YUCCA5 (PtYUC5), two enzymes in the auxin biosynthesis pathway. Overexpression of PtYUC4 enhanced drought tolerance, while simultaneous silencing of PtYUC4/5 evidently attenuated the drought tolerance of PtRD26_pro -IPT plants. Intriguingly, PtYUC4/5 displayed a conserved thioredoxin reductase activity that is required for drought tolerance by deterring reactive oxygen species accumulation. Our work reveals the molecular basis of cytokinin and auxin interactions in response to environmental stresses, and shed light on the improvement of drought tolerance without a growth penalty in trees by molecular breeding.

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.

Tobacco rattle virus-induced gene silencing in Hevea brasiliensis

Virus-induced gene silencing (VIGS) is a powerful gene-silencing tool that has been intensively applied in plants. To data, the application of VIGS in rubber tree has not yet been reported. In this study, we described the efficient gene silencing in rubber tree by VIGS. The gene encoding Hevea brasiliensis phytoene desaturase (HbPDS) was identified in rubber tree genome. Small interfering RNAs from HbPDS and the silencing gene fragment were predicted and a length of 399 bp was selected to be tested. We showed that the tobacco rattle virus (TRV)-VIGS could induce effective HbPDS silencing in rubber tree. This study was the first to report VIGS in rubber tree. The present TRV-VIGS method could be used to perform reverse genetic approaches to identify unknown gene functions and might be further applied to produce gene silenced rubber tree plants, to advance functional gene of rubber tree.

Virus-induced Gene Silencing in Streptocarpus rexii (Gesneriaceae)

Many members of the family Gesneriaceae are cultivated as ornamental plants, including Cape primrose (Streptocarpus) species. The range of plant architecture found in this genus has also made it a model to study leaf and meristem development and their evolution. However, the lack of tools to study gene functions through reverse genetics in Streptocarpus has limited the exploitation of its genetic potential. To aid functional genomic studies in Streptocarpus rexii, we sought to investigate virus-induced gene silencing (VIGS). Using the broad host range Tobacco Rattle Virus (TRV) to target the PHYTOENE DESATURASE (PDS) gene of S. rexii, we show that infection with sap from Nicotiana benthamiana triggered VIGS efficiently. VIGS was most effective in the seedling leaves 8 weeks after sowing, but was limited in duration and systemic spread. This study reports the first successful use of VIGS in Streptocarpus and in the family Gesneriaceae. The inoculation of viral sap derived from N. benthamiana was able to overcome the difficulties of standard Agrobacterium-mediated transformation in this genus. Irrespective of its transient effect, this VIGS system will be useful to assess gene function at the cellular level and represent an important tool for further understanding molecular mechanisms in Streptocarpus.

Virus-Induced Gene Silencing for Functional Analysis of Flower Traits in Petunia

Virus-induced gene silencing (VIGS) uses recombinant viruses to knock down the expression of endogenous plant genes, allowing for rapid functional analysis without generating stable transgenic plants. The Tobacco rattle virus (TRV) is a popular vector for VIGS because it has a wide host range that includes Petunia × hybrida (petunia), and it induces minimal viral symptoms. Using reporter genes like chalcone synthase (CHS) in tandem with a gene of interest (GOI; pTRV2-PhCHS-GOI), it is possible to visually identify silenced flowers so that phenotyping is more accurate. Inoculation methods and environmental conditions need to be optimized for each host plant-virus interaction to maximize silencing efficiency. This chapter will provide detailed protocols for VIGS in petunia, with an emphasis on the investigation of flower phenotypes.