Analysis of unique variable region of a plant root inducing plasmid, pRi1724, by the construction of its physical map and library

Genetic engineering and sustainable production of ornamentals: current status and future directions

Through the last decades, environmentally and health-friendly production methods and conscientious use of resources have become crucial for reaching the goal of a more sustainable plant production. Protection of the environment requires careful consumption of limited resources and reduction of chemicals applied during production of ornamental plants. Numerous chemicals used in modern plant production have negative impacts on human health and are hazardous to the environment. In Europe, several compounds have lost their approval and further legal restrictions can be expected. This review presents the more recent progress of genetic engineering in ornamental breeding, delivers an overview of the biological background of the used technologies and critically evaluates the usefulness of the strategies to obtain improved ornamental plants. First, genetic engineering is addressed as alternative to growth retardants, comprising recombinant DNA approaches targeting relevant hormone pathways, e.g. the gibberellic acid (GA) pathway. A reduced content of active GAs causes compact growth and can be facilitated by either decreased anabolism, increased catabolism or altered perception. Moreover, compactness can be accomplished by using a natural transformation approach without recombinant DNA technology. Secondly, metabolic engineering approaches targeting elements of the ethylene signal transduction pathway are summarized as a possible alternative to avoid the use of chemical ethylene inhibitors. In conclusion, molecular breeding approaches are dealt with in a way allowing a critical biological assessment and enabling the scientific community and public to put genetic engineering of ornamental plants into a perspective regarding their usefulness in plant breeding.

Agrobacterium rhizogenes GALLS protein substitutes for Agrobacterium tumefaciens single-stranded DNA-binding protein VirE2

Agrobacterium tumefaciens and Agrobacterium rhizogenes transfer plasmid-encoded genes and virulence (Vir) proteins into plant cells. The transferred DNA (T-DNA) is stably inherited and expressed in plant cells, causing crown gall or hairy root disease. DNA transfer from A. tumefaciens into plant cells resembles plasmid conjugation; single-stranded DNA (ssDNA) is exported from the bacteria via a type IV secretion system comprised of VirB1 through VirB11 and VirD4. Bacteria also secrete certain Vir proteins into plant cells via this pore. One of these, VirE2, is an ssDNA-binding protein crucial for efficient T-DNA transfer and integration. VirE2 binds incoming ssT-DNA and helps target it into the nucleus. Some strains of A. rhizogenes lack VirE2, but they still transfer T-DNA efficiently. We isolated a novel gene from A. rhizogenes that restored pathogenicity to virE2 mutant A. tumefaciens. The GALLS gene was essential for pathogenicity of A. rhizogenes. Unlike VirE2, GALLS contains a nucleoside triphosphate binding motif similar to one in TraA, a strand transferase conjugation protein. Despite their lack of similarity, GALLS substituted for VirE2.

Genes from Pseudomonas sp. strain BS involved in the conversion of L-2-amino-Delta(2)-thiazolin-4-carbonic acid to L-cysteine

DL-2-amino-Delta(2)-thiazolin-4-carbonic acid (DL-ATC) is a substrate for cysteine synthesis in some bacteria, and this bioconversion has been utilized for cysteine production in industry. We cloned a DNA fragment containing the genes involved in the conversion of L-ATC to L-cysteine from Pseudomonas sp. strain BS. The introduction of this DNA fragment into Escherichia coli cells enabled them to convert L-ATC to cysteine via N-carbamyl-L-cysteine (L-NCC) as an intermediate. The smallest recombinant plasmid, designated pTK10, contained a 2.6-kb insert DNA fragment that has L-cysteine synthetic activity. The nucleotide sequence of the insert DNA revealed that two open reading frames (ORFs) encoding proteins with molecular masses of 19.5 and 44.7 kDa were involved in the L-cysteine synthesis from DL-ATC. These ORFs were designated atcB and atcC, respectively, and their gene products were identified by overproduction of proteins encoded in each ORF and by the maxicell method. The functions of these gene products were examined using extracts of E. coli cells carrying deletion derivatives of pTK10. The results indicate that atcB and atcC are involved in the conversion of L-ATC to L-NCC and the conversion of L-NCC to cysteine, respectively. atcB was first identified as a gene encoding an enzyme that catalyzes thiazolin ring opening. AtcC is highly homologous with L-N-carbamoylases. Since both enzymes can only catalyze the L-specific conversion from L-ATC to L-NCC or L-NCC to L-cysteine, it is thought that atcB and atcC encode L-ATC hydrolase and N-carbamyl-L-cysteine amidohydrolase, respectively.

A novel plasmid curing method using incompatibility of plant pathogenic Ti plasmids in Agrobacterium tumefaciens

Ti (Tumor inducing) plasmids in Agrobacterium tumefaciens can transfer their T-DNA region into dicotyledonous plants, in which the expression of T-DNA genes causes plant tumors and the production of bacterial nutrients, e.g., opines such as nopaline. Naturally occurring Ti plasmids (pTi) are difficult to cure by conventional curing methods because of their high stability. Here, we developed a novel curing method based on plasmid incompatibility. For this, a curing plasmid, pMGTrep1, was newly constructed and subsequently introduced into A. tumefaciens strains harboring pTi by conjugation with Escherichia coli harboring pMGTrep1. The conjugation yielded 32-99% nopaline non-utilizing agrobacterial transconjugants in which pMGTrep1 replaced pTi due to incompatibility. Then, pMGTrep1-less derivatives of the transconjugants are easily selected in the presence of sucrose because pMGTrep1 contains a sucrose-sensitive sacB gene. This efficient method is directly applicable for curing plasmids with the same incompatibility group and shoud also applicable to other types of plasmids in Agrobacterium groups, including A. rhizogenes, by replacing the rep gene region of the curing plasmid with that of the corresponding incompatibility.

The complete nucleotide sequence of a plant root-inducing (Ri) plasmid indicates its chimeric structure and evolutionary relationship between tumor-inducing (Ti) and symbiotic (Sym) plasmids in Rhizobiaceae

The Ri (root-inducing) plasmid in Agrobacterium rhizogenes and Ti (tumor-inducing) plasmid in Agrobacterium tumefaciens have provided the fundamental basis for the construction of plant vectors and transgenic plants. Recently, the determination of the first complete nucleotide sequence of the Ti plasmid (pTi-SAKURA) has been successful. To understand the general structure of these oncogenic T-DNA transfer plasmids, the whole nucleotide sequence of a mikimopine-type Ri plasmid, pRi1724, was analyzed. The plasmid is 217,594 bp in size, and has 173 open reading frames (ORFs) in total, which are asymmetrically distributed. Except for 27 ORFs, which are unknown, 173 ORFs were classified into 12 groups as follows: three for DNA replication, nine for plasmid modification, 22 for conjugation, 26 for virulence, 11 for T-DNA gene, 19 for mikimopine/mikimopine-lactam transport, ten for an unknown opine metabolism, seven for transcriptional regulator, five for sugar transport, five for glycerol metabolism, four for chemoreceptor and 32 for others. The elucidated chimeric structure of pRi1724 interestingly indicates that the evolution of Rhizobiaceae plasmids seems to have kept interactions among the plasmids; especially, the genes and elements for a conjugal transfer of pRi1724 had clearly closer kinship to those of a Sym (symbiotic) plasmid, pNGR234a in Rhizobium sp. than those of Ti plasmids. By using sequencing and Northern analysis, we examined the metabolic pathway and gene expression of mikimopine, which is probably an Ri-specific opine.