ORE1 balances leaf senescence against maintenance by antagonizing G2-like-mediated transcription.

Leaf senescence is a key physiological process in all plants. Its onset is tightly controlled by transcription factors, of which NAC factor ORE1 (ANAC092) is crucial in Arabidopsis thaliana. Enhanced expression of ORE1 triggers early senescence by controlling a downstream gene network that includes various senescence-associated genes. Here, we report that unexpectedly ORE1 interacts with the G2-like transcription factors GLK1 and GLK2, which are important for chloroplast development and maintenance, and thereby for leaf maintenance. ORE1 antagonizes GLK transcriptional activity, shifting the balance from chloroplast maintenance towards deterioration. Our finding identifies a new mechanism important for the control of senescence by ORE1.

Plant regeneration of Korean wild ginseng (Panax ginseng Meyer) mutant lines induced by γ-irradiation ((60)Co) of adventitious roots.

An efficient in vitro protocol has been established for somatic embryogenesis and plantlet conversion of Korean wild ginseng (Panax ginseng Meyer). Wild-type and mutant adventitious roots derived from the ginseng produced calluses on Murashige and Skoog (MS) medium supplemented with 0.5 mg/L 2,4-dichlorophenoxyacetic acid and 0.3 mg/L kinetin; 53.3% of the explants formed callus. Embryogenic callus proliferation and somatic embryo induction occurred on MS medium containing 0.5 mg/L 2,4-dichlorophenoxyacetic acid. The induced somatic embryos further developed to maturity on MS medium with 5 mg/L gibberellic acid, and 85% of them germinated. The germinated embryos were developed to shoots and elongated on MS medium with 5 mg/L gibberellic acid. The shoots developed into plants with well-developed taproots on one-third strength Schenk and Hildebrandt basal medium supplemented with 0.25 mg/L 1-naphthaleneacetic acid. When the plants were transferred to soil, about 30% of the regenerated plants developed into normal plants.

Effects of field-grown genetically modified Zoysia grass on bacterial community structure.

Herbicide-tolerant Zoysia grass has been previously developed through Agrobacterium-mediated transformation. We investigated the effects of genetically modified (GM) Zoysia grass and the associated herbicide application on bacterial community structure by using culture-independent approaches. To assess the possible horizontal gene transfer (HGT) of transgenic DNA to soil microorganisms, total soil DNAs were amplified by PCR with two primer sets for the bar and hpt genes, which were introduced into the GM Zoysia grass by a callus-type transformation. The transgenic genes were not detected from the total genomic DNAs extracted from 1.5 g of each rhizosphere soils of GM and non-GM Zoysia grasses. The structures and diversities of the bacterial communities in rhizosphere soils of GM and non-GM Zoysia grasses were investigated by constructing 16S rDNA clone libraries. Classifier, provided in the RDP II, assigned 100 clones in the 16S rRNA gene sequences library into 11 bacterial phyla. The most abundant phyla in both clone libraries were Acidobacteria and Proteobacteria. The bacterial diversity of the GM clone library was lower than that of the non- GM library. The former contained four phyla, whereas the latter had seven phyla. Phylogenetic trees were constructed to confirm these results. Phylogenetic analyses of the two clone libraries revealed considerable difference from each other. The significance of difference between clone libraries was examined with LIBSHUFF statistics. LIBSHUFF analysis revealed that the two clone libraries differed significantly (P〈0.025), suggesting alterations in the composition of the microbial community associated with GM Zoysia grass.

Expression of the protective antigen for PEDV in transgenic duckweed, Lemna minor.

Duckweeds are small, floating aquatic plants with a number of useful characteristics, including edibility, fast-growing, and a clonal proliferation. Duckweed is also fed to animals as a diet complement because of its high nutritional value. Porcine epidemic diarrhea virus (PEDV) is a major causative agent of fatal diarrhea in piglets and is a serious problem in the hog-raising industry. In this study, we assessed the feasibility of producing a protective antigen for the PEDV spike protein 1 using duckweed, Lemna minor. Stably transformed Lemna were obtained by co-cultivation with A. tumefaciens EHA105 harboring the PEDV spike protein gene. Transgene integration and expression of the PEDV spike protein 1 gene were confirmed by genomic PCR and RT-PCR and western blot analysis of transgenic Lemna, respectively. This is the first report of the expression of a vaccine antigen against an animal infectious disease in duckweed.

Ginsenoside Production and Morphological Characterization of Wild Ginseng (Panax ginseng Meyer) Mutant Lines Induced by γ-irradiation ((60)Co) of Adventitious Roots.

With the purpose of improving ginsenoside content in adventitious root cultures of Korean wild ginseng (Panax ginseng Meyer), the roots were treated with different dosages of γ-ray (5, 10, 25, 50, 75, 100, and 200 Gy). The growth of adventitious roots was inhibited at over 100 Gy. The irradiated adventitious roots showed significant variation in the morphological parameters and crude saponin content at 50 to100 Gy. Therefore, four mutant cell lines out of the propagation of 35 cell lines treated with 50 Gy and 100 Gy were selected on the basis of phenotypic morphology and crude saponin contents relative to the wild type control. The contents of 7 major ginsenosides (Rg1, Re, Rb1, Rb2, Rc, Rf, and Rd) were determined for cell lines 1 and 3 from 100 Gy and lines 2 and 4 from 50 Gy treatments. Cell line 2 showed more secondary roots, longer length and superior growth rate than the root controls in flasks and bioreactors. Cell line 1 showed larger average diameter and the growth rate in the bioreactor was comparable with that of the control but greater in the flask cultured roots. Cell lines 1 and 2, especially the former, showed much more ginsenoside contents than the control in flasks and bioreactors. Therefore, we chose cell line 1 for further study of ginsenoside contents. The crude saponin content of line 1 in flask and bioreactor cultures increased by 1.4 and 1.8-fold, respectively, compared to the control. Total contents of 7 ginsenoside types (Rg1, Re, Rb1, Rb2, Rc, Rf, and Rd) increased by 1.8 and 2.3-fold, respectively compared to the control. Crude saponin and ginsenoside contents in the bioreactor culture increased by about 1.4-fold compared to that the flask culture.

Isolation of carbon- and nitrogen-deprivation-induced loci of Sinorhizobium meliloti 1021 by Tn5-luxAB mutagenesis.

Soil bacteria, such as Sinorhizobium meliloti, are subject to variation in environmental conditions, including carbon- and nitrogen-deprivation. The ability of bacteria to sense changes in their environment and respond accordingly is of vital importance to their survival and persistence in the soil and rhizosphere. A derivative of Tn5 which creates transcriptional fusions to the promoterless luxAB genes was used to mutagenize S. meliloti 1021 and 5000 insertion mutants were subsequently screened for gene fusions induced by selected environmental stresses. The isolation of 21 gene fusions induced by nitrogen-deprivation and 12 induced by carbon-deprivation is described. Cloning and partial DNA sequence analysis of the transposon-tagged loci revealed a variety of novel genes, as well as S. meliloti genes with significant similarity to known bacterial loci. In addition, nodule occupancy studies were carried out with selected Tn5-luxAB insertion mutants to examine the role of the tagged genes in competition.