Stable transformation ofArabidopsis with thebar gene using particle bombardment

Effects of Arabidopsis Ku80 deletion on the integration of the left border of T-DNA into plant chromosomal DNA via Agrobacterium tumefaciens

T-DNA integration into plant chromosomal DNA via Agrobacterium tumefaciens can be achieved by exploiting the double-strand break repair system of the host's DNA. However, the detailed mechanism of T-DNA integration remains unclear. Here, a sequence analysis of the junction sequences of T-DNA and chromosomal DNA was performed to assess the mechanism of T-DNA integration. T-DNA was introduced into Arabidopsis wild-type and NHEJ-deficient ku80 mutant plants using the floral dip method; the junctions of the left border (LB) of T-DNA were subsequently analyzed by adapter PCR. The most frequent junction of the LB of T-DNA with chromosomal DNA was of the filler DNA type in both lines. The lengths of direct or inverted repeat sequences within or around the filler DNA sequence were greater in the ku80 mutant. In addition, the frequency of T-DNA integration near a transcription start site was significantly higher in the ku80 mutant. Our observations suggest that the presence of the Ku80 protein affects the location of the integration of T-DNA and the pattern of formation of repeat sequences within or around the filler DNA during LB integration into chromosomal DNA.

Suppressed expression of choline monooxygenase in sugar beet on the accumulation of glycine betaine

Glycine betaine (GB) is an important osmoprotectant and synthesized by two-step oxidation of choline. Choline monooxygenase (CMO) catalyzes the first step of the pathway and is believed to be a rate limiting step for GB synthesis. Recent studies have shown the importance of choline-precursor supply for GB synthesis. In order to investigate the role of CMO for GB accumulation in sugar beet (Beta vulgaris), transgenic plants carrying the antisense BvCMO gene were developed. The antisense BvCMO plants showed the decreased activity of GB synthesis from choline compared to wild-type (WT) plants which is well related to the suppressed level of BvCMO protein. However, GB contents were similar between transgenic and WT plants with the exception of young leaves and storage roots. Transgenic plants showed enhanced susceptibility to salt stress than WT plants. These results suggest the importance of choline-precursor-supply for GB accumulation, and young leaves and storage root are sensitive sites for GB accumulation.

Arabidopsis Mutants by Activation Tagging in which Photosynthesis Genes are Expressed in Dedifferentiated Calli

In an effort to delineate the precise mechanisms underlying the organ-specific expression of photosynthesis genes, Arabidopsis lines homozygous for each transgene construct made with the gene for hygromycin B phosphotransferase or beta-glucuronidase (GUS) placed under control of the promoter of the nuclear gene for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RBCS-3B) were constructed. Furthermore, activation tagging with T-DNA possessing quadruply repeated enhancers derived from the cauliflower mosaic virus 35S promoter was applied to a transgenic line of Arabidopsis. Mutants resistant to hygromycin B during the growth of calli generated from non-green roots on callus-inducing medium resulted from the expression of hygromycin B phosphotransferase driven by the RBCS-3B promoter. Three mutant lines, ces101 to ces103 (callus expression of RBCS), were obtained from approximately 4,000 calli resistant to a selectable marker for transformation. The active transcription driven by the RBCS-3B promoter in all the calli of ces mutants was confirmed by expression of both the GUS reporter gene and endogenous RBCS-3B. Chlorophyll and carotenoids, as well as light-dependent O(2) evolution, have been detected in the calli of all ces mutants. The loci where T-DNA was integrated in the ces101 line were determined by thermal asymmetric interlaced (TAIL)-PCR. The introduction of a DNA fragment harboring the gene for receptor-like kinase placed under the influence of enhancers into the parental line reproduced the phenotype of ces mutants. We have thus concluded that CES101 is a receptor-like kinase. The strategy presented in this investigation may promise to select a greater number of ces mutants.

A phosphonate-induced gene which promotes Penicillium-mediated bioconversion of cis-propenylphosphonic acid to fosfomycin

Penicillium decumbens is able to epoxidize cis-propenylphosphonic acid (cPA) to produce the antibiotic fosfomycin [FOM; also referred to as phosphonomycin and (-)-cis-1,2-epoxypropylphosphonic acid], a bioconversion of considerable commercial significance. We sought to improve the efficiency of the process by overexpression of the genes involved. A conventional approach of isolating the presumed epoxidase and its corresponding gene was not possible since cPA epoxidation could not be achieved with protein extracts. As an alternative approach, proteins induced by cPA were detected by two-dimensional gel electrophoresis. The observation that a 31-kDa protein (EpoA) was both cPA induced and overaccumulated in a strain which more efficiently converted cPA suggested that it might take part in the bioconversion. EpoA was purified, its amino acid sequence was partially determined, and the corresponding gene was isolated from cosmid and cDNA libraries with oligonucleotide probes. The DNA sequence for this gene (epoA) contained two introns and an open reading frame encoding a peptide of 277 amino acids having some similarity to oxygenases. When the gene was subcloned into P. decumbens, a fourfold increase in epoxidation activity was achieved. epoA-disruption mutants which were obtained by homologous recombination could not convert cPA to FOM. To investigate the regulation of the epoA promoter, the bialaphos resistance gene (bar, encoding phosphinothricin acetyltransferase) was used to replace the epoA-coding region. In P. decumbens, expression of the bar reporter gene was induced by cPA, FOM, and phosphorous acid but not by phosphoric acid.

Structures of transgene loci in transgenic Arabidopsis plants obtained by particle bombardment: junction regions can bind to nuclear matrices

To clarify the molecular structure of the integration sites of transgenes, we used particle bombardment to examine the DNA sequences of transgene loci. Three transgenic Arabidopsis lines gave a single Southern hybridization band with a selectable gene as the probe. Junction regions flanked by the transgenes were cloned by the inverse polymerase chain reaction method, and the characteristics of the DNA sequences of the 10 junction regions were investigated. All but two of these were AT-rich sequences bearing motifs characteristic of a scaffold/matrix-attachment region (S/MAR). Calculations showed that seven of them should have a propensity for curvature. An assay of in-vitro binding to tobacco nuclear matrices showed that all the junction regions bound to nuclear matrices and that the two input DNAs did not bind. The 12 chromosome/transgene (CT) junctions in these three transgene loci were investigated. Cleavage sites for topoisomerase I were found at 10 of the 12, near the junction point. The other two junctions had sites within 6bp of the junction point. The sequence near one terminal of the transgene in the transgene loci was compared with that near the other terminal. Short, direct repeats consisting of 4-6bp were present within 10bp of the junction points in the sequence. We speculate that the transgene introduced by particle bombardment is delivered on AT-rich S/MAR that has a propensity for curvature, and then a nucleotide near the short, direct repeat on the transgene is joined near the cleavage sites on the genome for topoisomerase I.