Jeung-Sul Han

Expression of an Arabidopsis Ca2+/H+ antiporter CAX1 variant in petunia enhances cadmium tolerance and accumulation.

Phytoremediation is a cost-effective and minimally invasive technology to cleanse soils contaminated with heavy metals. However, few plant species are suitable for phytoremediation of metals such as cadmium (Cd). Genetic engineering offers a powerful tool to generate plants that can hyperaccumulate Cd. An Arabidopsis CAX1 mutant (CAXcd), which confers enhanced Cd transport in yeast, was ectopically expressed in petunia to evaluate whether the CAXcd expression would enhance Cd tolerance and accumulation in planta. The CAXcd-expressing petunia plants showed significantly greater Cd tolerance and accumulation than the controls. After being treated with either 50 or 100μM CdCl(2) for 6 weeks, the CAXcd-expressing plants showed more vigorous growth compared with controls, and the transgenic plants accumulated significantly more Cd (up to 2.5-fold) than controls. Moreover, the accumulation of Cd did not affect the development and morphology of the CAXcd-expressing petunia plants until the flowering and ultimately the maturing of seeds. Therefore, petunia has the potential to serve as a model species for developing herbaceous, ornamental plants for phytoremediation.

Modest calcium increase in tomatoes expressing a variant of Arabidopsis cation/H+ antiporter

The over-expression of Arabidopsis CAX1 and CAX2 causes transgenic tomato plants to reveal severe Ca2+ deficiency-like symptoms such as tip-burn and/or blossom end rot, despite there being sufficient Ca2+ in each plant part. To correct the symptoms and to moderately enhance the calcium level, a worldwide vegetable tomato was genetically engineered using a modified Arabidopsis cation/H+ antiporter sCAX2A, a mutant form of Arabidopsis CAX2. Compared with the wild-type, the sCAX2A-expressing tomato plants demonstrated elevated Ca2+ levels in the fruits with almost no changes in the levels of Mn2+, Cu2+, and Fe2+. Moreover, expression of sCAX2A in tomato plants did not show any significant alterations in their morphological phenotypes. Unlike 35S::sCAX1 construct, sCAX2A antiporter gene driven by 35S promoter can be a valuable tool for enriching Ca2+ contents in the tomato fruit without additional accumulation of the undesirable cations.

Elimination of Chrysanthemum stunt viroid (CSVd) from meristem tip culture combined with prolonged cold treatment

Chrysanthemum production in Korea has recently been greatly affected by the spread of Chrysanthemum stunt viroid (CSVd) infection, necessitating the use of CSVd-free stocks to ensure successful chrysanthemum cultivation. We investigated the effects of low temperature (4°C), antiviral chemicals (ribavirin and amantadine) and a combination of these treatments on CSVd elimination by meristem tip cultures using plantlets that originated from CSVd-infected chrysanthemum ‘Ency’. Neither antiviral agents led to CSVd elimination, despite the suppression of meristem tip growth in a concentration dependent manner. However, the CSVd elimination rate increased up to 42.8% when meristem tips were excised after storage at 4°C for two months. The most effective results were obtained from a combination of low temperature for three months at 4°C followed by meristem tip culture on media containing 50 and 100 mg·L−1 ribavirin. These results suggest that antiviral agents can also be useful for CSVd elimination if their treatment is combined with prolonged periods of low temperature. This is the first report of eradication of viroids from spray type chrysanthemum bred in Korea.

Factors influencing in vitro shoot regeneration from leaf segments of Chrysanthemum

The objective of this research was to develop an efficient protocol for shoot regeneration from leaf segments of the Chrysanthemum cv. Vivid Scarlet by examining the effects of plant growth regulators, dark incubation period, gelling agents, and silver nitrate. The highest number of shoots per explant (12.3) was regenerated from leaf explants cultured on Murashige and Skoog (MS) medium supplemented with a combination of 1 mgL(-1) of 6-benzyladenine (BA) and 2 mgL(-1) of α-naphthaleneacetic acid (NAA) under light conditions without any initial dark period. Gelrite was the most effective gelling agent for shoot regeneration among those tested, whereas the presence of silver nitrate distinctly inhibited shoot regeneration. Superior plant growth and rooting was observed on a hormone-free MS medium solidified with Gelrite. Flow cytometry analysis revealed no ploidy variation between the regenerated plants and the mother plant grown under greenhouse conditions. The established protocol was applicable to shoot regeneration for four out of six cultivars tested. This research will facilitate the genetic transformation and micropropagation of Chrysanthemum cultivars.

Increased biomass and enhanced tolerance to salt stress in Chinese cabbage overexpressing Arabidopsis H + -PPase (AVP1)

On the basis of the reported agriculturally valuable phenotypes resulted from ectopic overexpression of Arabidopsis vacuolar W-PPase (AVP 1), we generated the Chinese cabbage lines expressing AVP I which then subjected to salt stress to determine the A V P1 expression if it consistently confers the capability for increasing biomass and enhancing tolerance to salinity in other species. Collectively, here we demonstrate that the transgenic young plants show more vigorous growth and higher tolerance to salt stress than wild-type ones. Increased biomass phenotype by A VP1 expression was supported by comparing fresh and dry weights of transgenic and wild type plants grown under normal condition, while higher salt tolerance trait was confirmed by tracing the kinetics of photosystem II quantum yield and DAB-staining under gradually intensified salt stress induced by MS salt or NaCl, followed by normal condition.

Ectopic expression of a maize calreticulin mitigates calcium deficiency-like disorders in sCAX1-expressing tobacco and tomato.

Deregulated expression of an Arabidopsis H+/Ca2+ antiporter (sCAX1) in agricultural crops increases total calcium (Ca2+) but may result in yield losses due to Ca2+ deficiency-like symptoms. Here we demonstrate that co-expression of a maize calreticulin (CRT, a Ca2+ binding protein located at endoplasmic reticulum) in sCAX1-expressing tobacco and tomato plants mitigated these adverse effects while maintaining enhanced Ca2+ content. Co-expression of CRT and sCAX1 could alleviate the hypersensitivity to ion imbalance in tobacco plants. Furthermore, blossom-end rot (BER) in tomato may be linked to changes in CAX activity and enhanced CRT expression mitigated BER in sCAX1 expressing lines. These findings suggest that co-expressing Ca2+ transporters and binding proteins at different intracellular compartments can alter the content and distribution of Ca2+ within the plant matrix.

Role of Nano-silver and the Bacterial Strain Enterobacter cloacae in Increasing Vase Life of Cut Carnation ‘Omea’

We investigated the role of nano-silver (NAg) and the bacterial strain Enterobacter cloacae in increasing the vase life of cut carnation flowers ‘Omea.’ NAg treatment extended vase life of the flowers by increasing relative fresh weight, antioxidant activities, and expression level of the cysteine proteinase inhibitor gene (DcCPi), and by suppressing bacterial blockage in stem segments, ethylene production and expression of ethylene biosynthesis genes and DcCP1 gene, compared with the control. Out of all the treatments, administration of 25 mg L-1 NAg gave the best results for all the analyzed parameters. Interestingly, application of E. cloacae also extended the vase life of cut flowers by 3 days in comparison with control flowers, and overall, showed better results than the control for all the analyzed parameters. Taken together, these results demonstrate the positive role of NAg and E. cloacae in increasing the longevity of cut carnation flowers, and indicate that this effect is brought about through multiple modes of action.

Physiological responses to drought stress of transgenic Chinese cabbage expressing Arabidopsis H+-pyrophosphatase

Plant tolerance to drought is a beneficial trait for stabilizing crop productivity under water deficits. Here we report that genetically engineered Chinese cabbage expressing Arabidopsis H-pyrophosphatase (AVP1) shows enhanced physiological parameters related to drought tolerance. In comparison with wild type plants under soil water deficit stress created by cessation of irrigation, soil water potential in pot with AVP1-expressing plants was more rapidly decreased that might lead to increased relative water content in leaves, while both genotypes had indistinguishable wilting phenotypes. Transgenic plants subjected to drought treatment also exhibited higher photosystem II quantum yield in addition to lower electrolyte leakage and H2O2-3,3’-diaminobenzidine content when compared to wild type plants.

Suppression of tobamovirus movement toward upper leaves in the tomato plant over-expressing a maize calreticulin

【To ascertain the effect of over-expressed maize calreticulin in tomato plant on tobamovirus movement in addition to validating potentiality of the gene (ZmCRT) as a means for the virus-resistance resource, four ZmCRT-expressing homozygous lines were generated from the T0 plants as using an Agrobacterium-mediated transformation, nucleic acid analyses, and a conventional breeding method. Of them, a line was subjected to the bioassay for tolerances to tobacco mosaic virus-U1 (TMV-U1) and tomato mosaic virus (ToMV) followed by RT-PCR and a chlorophyll fluorescence quenching analyses. Both transgenic plants transcribing ZmCRT and wild-type plants showed no symptom by 20 days after viruses inoculation, however the photosystem II quantum yield parameter measured from the upper leaves of ToMV-inoculated plants revealed that ZmCRT transgenic plants have higher photosynthetic ability than wild-type ones at that time, which indirectly implies that over-expressed ZmCRT product acts as a barrier to the cell-to-cell and/or systemic movement of ToMV. Moreover, ZmCRT transgenic plants showed remarkably longer shoot length than wild-type ones in 40 days after TMV-U1 or ToMV inoculation each, which might be resulted from higher photosynthetic ability during the phase not yet showing any external symptoms. Collectively, over-expressed ZmCRT protein in tomato plants is able to interrupt the systemic movement of infected TMV-U1 and ToMV even though not perfect.】

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

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