Construction of whole genome radiation hybrid panels and map of chromosome 5A of wheat using asymmetric somatic hybridization.

To explore the feasibility of constructing a whole genome radiation hybrid (WGRH) map in plant species with large genomes, asymmetric somatic hybridization between wheat (Triticum aestivum L.) and Bupleurum scorzonerifolium Willd. was performed. The protoplasts of wheat were irradiated with ultraviolet light (UV) and gamma-ray and rescued by protoplast fusion using B. scorzonerifolium as the recipient. Assessment of SSR markers showed that the radiation hybrids have the average marker retention frequency of 15.5%. Two RH panels (RHPWI and RHPWII) that contained 92 and 184 radiation hybrids, respectively, were developed and used for mapping of 68 SSR markers in chromosome 5A of wheat. A total of 1557 and 2034 breaks were detected in each panel. The RH map of chromosome 5A based on RHPWII was constructed. The distance of the comprehensive map was 2103 cR and the approximate resolution was estimated to be ∼501.6 kb/break. The RH panels evaluated in this study enabled us to order the ESTs in a single deletion bin or in the multiple bins cross the chromosome. These results demonstrated that RH mapping via protoplast fusion is feasible at the whole genome level for mapping purposes in wheat and the potential value of this mapping approach for the plant species with large genomes.

Hybrid inflorescences derived from gamma-fusion of Arabidopsis thaliana with Bupleurum scorzonerifolium.

In our early experiments, a variety of Bupleurum scorzonerifolium-like somatic hybrid plants were obtained from protoplast fusion between Arabidopsis thaliana and UV-treated/untreated B. scorzonerifolium. To compare the effects of UV and γ-ray irradiation on the B. scorzonerifolium partner and obtain Arabidopsis-like hybrids, we designed a novel combination of somatic hybridization between A. thaliana and B. scorzonerifolium. Before protoplast isolation and fusion, the suspension cells of B. scorzonerifolium were irradiated by gamma ray ((60)Co, 50 Gy with 1.3 Gy min(-1)). Both parental protoplasts lost regeneration capacity, but over 100 somatic hybrids restored the capacity and developed to Arabidopsis-like inflorescences and flowers with some characteristics of B. scorzonerifolium. Some hybrid flowers showed yellow sepal, petal, or carpel, whose color was similar to the petal of B. scorzonerifolium; the others had silique of Arabidopsis with angularity of B. scorzonerifolium, and their parts possessed five stamens, the same as B. scorzonerifolium. Cytological analysis showed that three hybrids had Arabidopsis-like karyotypes. Random Amplified Polymorphic DNA (RAPD) and Simple Sequence Repeats (SSR) profiles revealed that both parental fragments were amplified from these hybrids. These results indicated chromatin introgression from B. scorzonerifolium to A. thaliana, which may be related to the complementation of hybrid inflorescence and flower generation.

Ginsenoside Rb1 in asymmetric somatic hybrid calli of Daucus carota with Panax quinquefolius.

American ginseng (Panax quinquefolius L.) is one of the most valuable herbs in the world. Its major active components are ginsenosides. In order to produce ginsenoside heterogeneously, somatic hybridization, a novel approach for genetic introgression, was employed in this study. Protoplasts derived from respective calli of carrot (Daucus carota var. sativus Hoffm.) and American ginseng (P. quinquefolius L.) were used as the fusion partners. Hybrid calli derived from single cell lines containing chromatin of American ginseng were confirmed by the analyses of isozyme, Random amplified polymorphic DNA (RAPD) and genomic in situ hybridization (GISH). High performance liquid chromatography (HPLC) results showed that the ginseng monomer Rb(1) was synthesized in seven of the hybrid calli identified as well as in the parent American ginseng calli but not in the parent carrot calli. Results indicated that hybrid introgression lines could produce ginsenoside Rb(1) and the ginsenoside Rb(1) biosynthesis pathway has been introgressed into carrot cells via somatic hybridization. From the point of biosafety view concerning the consumer acceptance, the potential predominance to produce ginsenosides with somatic hybridization other than with genetic transformation is discussed.

Genotyping of somatic hybrids between Festuca arundinacea Schreb. and Triticum aestivum L.

In order to genotype hybrid genomes of distant asymmetric somatic hybrids, we synthesized hybrid calli and plants via PEG-mediated protoplast fusion between recipient tall fescue (Festuca. arundinacea Schreb.) and donor wheat (Triticum aestivum L.). Seventeen and 25 putative hybrid clones were produced from the fusion combinations I and II, each with the donor wheat protoplast treated by UV light for 30 s and 1 min, respectively. Isozyme and RAPD profiles confirmed that ten hybrid clones were obtained from combination I and 19 from combination II. Out of the 29 hybrids, 12 regenerated hybrid plants with tall fescue phenotype. Composition and methylation-variation of the nuclear and cytoplasmic genomes of some hybrids, either with or without regenerative ability, were compared by genomic in situ hybridization, restriction fragment length polymorphism, and DNA methylation-sensitive amplification polymorphism. Our results indicated that these selected hybrids all contained introgressed nuclear and cytoplasmic DNA as well as obvious methylation variations compared to both parents. However, there were no differences either in nuclear/cytoplasmic DNA or methylation degree between the regenerable and non-regenerable hybrid clones. We conclude that both regeneration complementation and genetic material balance are crucial for hybrid plant regeneration.

Enhanced salt tolerance of transgenic progeny of tall fescue (Festuca arundinacea) expressing a vacuolar Na+/H+ antiporter gene from Arabidopsis.

Salinity is a major abiotic stress factor limiting crop production. To generate salt-tolerant turf and forage, we had transformed tall fescue (Festuca arundinacea) with AtNHX1, a vacuolar Na(+)/H(+) antiporter gene from Arabidopsis thaliana. In this paper, we report that overexpression of the AtNHX1 gene confers enhanced salt tolerance to the transformed tall fescue progenies. DNA gel blot analysis and reverse transcription (RT) polymerase chain reaction (PCR) were carried out to confirm the inheritance and expression of the AtNHX1 gene in transgenic T(1) and T(2) lines. These transgenic lines showed no phenotypic changes or yield reduction. Plants carrying the AtNHX1 gene were more resistant to a 20 mM NaCl solution than control plants. The roots of the transgenic lines had a higher sodium content than controls, due to an increased Na(+)/H(+) antiporter activity in tonoplast vesicles. Our results suggest that this accumulation of sodium in vacuoles of root cells, mediated by vacuolar Na(+)/H(+) antiporters, reduced the toxic effects of salinity to tall fescue and thus enhanced its salt tolerance.

Arabidopsis DREB1A/CBF3 bestowed transgenic tall fescue increased tolerance to drought stress.

In order to improve drought tolerance of tall fescue (Festuca arundinacea Schreb.), an important perennial cool-season grass, we introduced Arabidopsis DREB1A/CBF3 driven by the inducible rd29A promoter into tall fescue mediated by Agrobacterium tumefaciens strains AGL1. PCR and Southern blot analysis confirmed that DREB1A/CBF3 gene had been integrated into the genome of tall fescue. AtDREB1A gene was stably inherited and expressed in T(1) plants, as indicated by PCR, RT-PCR and Western blotting analysis. The transgenic plants also showed an increased expression of AtP5CS2, which was confirmed to be a downstream target gene of DREB in Arabidopsis. We found that the transgenic tall fescue showed increased resistance to drought and accumulated high level of proline, indicating ability of the CBF3 gene to induce stress related response in tall fescue. The result here provides evidence for drought improvement of tall fescue via transformation with stress-related transcription factor and stress-induced promoter.

Analysis of remote asymmetric somatic hybrids between common wheat and Arabidopsis thaliana.

Callus-derived protoplasts of common wheat (Triticum aestivum L. cv. Hesheng 3) irradiated with ultraviolet light were fused by using the PEG method with cell suspension-derived protoplasts of Arabidopsis thaliana. Regenerated calli and green plants resembling that of wheat were obtained. The hybrid nature of putative calli and plants were confirmed by isozyme, random amplified polymorphic DNA and genomic in situ hybridization (GISH) analyses. GISH results indicated that 1 approximately 3 small chromosome fragments of A. thaliana were found introgression into the terminals of wheat chromosomes, forming highly asymmetric hybrids. Cytoplasmic genome tests did not show any cytoplasmic genetic materials from A. thaliana. However, variations from the normal wheat cytoplasmic genome were found, indicating recombination or rearrangement occurred during the process of somatic hybridization. The chromosome elimination in the asymmetric somatic hybridization of remote phylogenetic relationship was discussed. A miniature inverted-repeat transposable element related sequence was found by chance in the hybrids which might accompany and impact the process of somatic hybridization.

Genetic characterization of asymmetric somatic hybrids between Bupleurum scorzonerifolium Willd and Triticum aestivum L.: potential application to the study of the wheat genome.

In this paper, we describe how Bupleurum scorzonerifolium/Triticum aestivum asymmetric somatic hybrids can be exploited to study the wheat genome. Protoplasts of B. scorzonerifolium Willd were irradiated with ultraviolet light (UV) and fused with protoplasts of common wheat (T. aestivum L.). All cell clones were similar in appearance to those of B. scorzonerifolium, while the regenerated plantlets were either intermediate or B. scorzonerifolium-like. Genotypic screening using isozymes showed that 39.3% of cell clones formed were hybrid. Some of the hybrid cell clones grew vigorously, and differentiated green leaves, shoots or plantlets. DNA marker analysis of the hybrids demonstrated that wheat DNA was integrated into the nuclear genomes of B. scorzonerifolium and in situ karyotyping cells revealed that a few wheat chromosome fragments had been introgressed into B. scorzonerifolium. The average wheat SSR retention frequency of the RH panel was 20.50%, but was only 6.67% in fusions with a non-irradiated donor. B. scorzonerifolium chromosomes and wheat SSR fragments in most asymmetric hybrid cell lines remained stable over a period of 2.5-3.5 years. We suggest the UV-induced asymmetric somatic hybrids between B. scorzonerifolium Willd and T. aestivum L. have the potential for use in the construction of an RH map of the wheat genome.

Intracellular FITC-derivatization with PEG.

In order to investigate the amino acids (AAs) in plant cells, we explore an avenue for intracellular derivatization with FITC. In this method, FITC was used to mark AAs in living protoplasts derived from embryogenic calli of common wheat (Triticum aestivum L. c.v. Jinan 177) mediated by PEG. After FITC-derivatization, the AAs in the lysate were determined by CE. The result reveals that this PEG method can be used to transfer FITC into plant cells efficiently, which provides a good method for AA analysis in plant cells.

[Research on Festuca arundinacea transformation mediated by Agrobacterium tumefaciens].

The embryo-derived calli from four types of tall fescues (Festuca arundinacea Schreb) were transformed with two Agrobactrium tumefaciens strains AGL1 and GV3101. AGL1 harbors an intron-AtNHX1 expression vector pROK2U containing ubiqutin promoter and npt II marker gene. GV3101 harbors an intron-AtNHX1 expression vector pROK2 containing 35S promoter and npt II gene. After infection and co-culture with AGL1 or GV3101, the embyogenic calli were selected with 50-150 mg/L paromomycine and 1126 resistant plants regenerated from the resistant calli. All plants were selected further with 10-20 mg/L Kanamycin and 525 of them remained green. Genome DNA of the resistant plants was checked with specific primers and probe from AtNHX1 gene. The results of PCR assay and Southern blot analysis indicted that exogenous target gene (AtNHX1 gene) had been transferred into different cultivars of Festuca arundinacea. Different transformation frequencies among the four cultivars were obtained.

Regeneration of somatic hybrids in relation to the nuclear and cytoplasmic genomes of wheat and Setaria italica.

Somatic hybridization via PEG (Polyethylene 6000)-mediated protoplast fusion was achieved between two different wheat culture lines (Triticum aestivum L., "Jinan"177, T1 and T2) and Setaria italica (L.) P. Beauv. The T1 recipient originated from non-regenerable long-term cell suspensions, while T2 was derived from embryogenic calli with a high regeneration capacity. Donor protoplasts were obtained from embryogenic calli of S. italica (S) (with low regeneration capacity) irradiated with different doses of ultraviolet light. Twenty-three putative hybrid cell lines were produced in fusion combinations with the donor protoplasts treated with UV light for 30 s (combination I) and 1 min (combination II), but only one (from combination II) differentiated into green plants. Three cell lines from combination I and five cell lines from combination II possessed the nuclear genomes of T1, T2, and S. italica as revealed by cytological, isozyme, RAPD, and 5S rDNA spacer sequence analyses. Genomic in situ hybridization (GISH) analysis showed that most hybrid cell lines had 22-36 wheat chromosomes, 0-2 S. italica chromosomes, and 1-6 wheat - S. italica recombinant chromosomes, whereas the regenerable cell line had 44-56 wheat chromosomes and 3-6 recombinant chromosomes, but no intact S. italica chromosomes. RFLP analysis of organellar DNA revealed that mitochondrial and chloroplast DNA of both parents coexisted in all hybrid cell lines and recombined in most hybrid cell lines. These results indicate that the regeneration of hybrid plants involves not only the integration of S. italica nuclear and organellar DNA, but also the genome complementation of T1 and T2.

[Somatic hybridization between carrot and Bupleurum scorzonerifolium and esteras isoenzyme analysis].

OBJECTIVE: To transfer the effective elements of Bupleurum scorzonerifolium into carrot, and provide theoretical data for the exploitation, improvement and selection of the germplasm of Chinese medicinal plants. METHOD: The protoplasta of Bupleurum scorzonerifolium irradiated by ultraviolet light (UV) at an intensity of 300 microW.(cm2)-1 for 0, 1, 2 min respectively were fused with those of carrot Fisch by PEG method. The regenerated clones, derived form a single fused cell, were examined for their hybrid nature by phenotype and Esterase isoenzyme analysis. RESULT: Nine clones were identified as the somatic hybrids between B. scorzonerifolium and carrot. CONCLUSION: This provides a firm foundation for the further analysis of the main active components saikosaponin of somatic hybrids and the screening out of high-medicine-content hybrid cell lines.