RESUMEN
Crown gall disease, caused by the soil bacterium Agrobacterium tumefaciens, results in significant economic losses in perennial crops worldwide. A. tumefaciens is one of the few organisms with a well characterized horizontal gene transfer system, possessing a suite of oncogenes that, when integrated into the plant genome, orchestrate de novo auxin and cytokinin biosynthesis to generate tumors. Specifically, the iaaM and ipt oncogenes, which show approximately 90% DNA sequence identity across studied A. tumefaciens strains, are required for tumor formation. By expressing two self-complementary RNA constructions designed to initiate RNA interference (RNAi) of iaaM and ipt, we generated transgenic Arabidopsis thaliana and Lycopersicon esculentum plants that are highly resistant to crown gall disease development. In in vitro root inoculation bioassays with two biovar I strains of A. tumefaciens, transgenic Arabidopsis lines averaged 0.0-1.5% tumorigenesis, whereas wild-type controls averaged 97.5% tumorigenesis. Similarly, several transformed tomato lines that were challenged by stem inoculation with three biovar I strains, one biovar II strain, and one biovar III strain of A. tumefaciens displayed between 0.0% and 24.2% tumorigenesis, whereas controls averaged 100% tumorigenesis. This mechanism of resistance, which is based on mRNA sequence homology rather than the highly specific receptor-ligand binding interactions characteristic of traditional plant resistance genes, should be highly durable. If successful and durable under field conditions, RNAi-mediated oncogene silencing may find broad applicability in the improvement of tree crop and ornamental rootstocks.
Asunto(s)
Arabidopsis/genética , Proteínas Bacterianas , Silenciador del Gen/fisiología , Oncogenes , Tumores de Planta/genética , ARN de Planta/fisiología , Solanum lycopersicum/genética , ADN de Plantas/genética , Genes Bacterianos , Ácidos Indolacéticos/genética , Rhizobium/genética , Transformación GenéticaRESUMEN
Co-transformation was investigated as a method that would allow the use of a selectable marker during plant regeneration followed by recovery of progeny which contain the desired gene(s) but lack a marker gene. Rapeseed (Brassica napus cv `212/86') and tobacco (Nicotiana tabacum cv `Xanthi NC') were co-cultivated with a single Agrobacterium tumefaciens strain containing two binary plasmids. Genes from both plasmids were expressed in approximately 50% of the primary transformants. Progeny expressing only one of the transgenes were observed in about 50% of the co-transformed lines, indicating that the genes were inserted at different loci. This single-strain co-transformation method allowed the use of a selectable marker during plant regeneration and subsequent recovery of marker-free progeny.
RESUMEN
The cloning and sequencing of two cDNAs representing pectinmethylesterase (PME) RNAs from tomato fruit is reported. The clones were used to construct chimeric antisense PME genes designed for high-level constitutive expression in plants. A full-length antisense PME gene construct, in conjunction with a chimeric antisense polygalacturonase gene, was introduced into tomato plants via Agrobacterium-mediated transformation. Simultaneous and significant reduction in the mRNA and protein levels of these normally highly abundant cell wall hydrolases of the pectin degradation pathway were observed in ripe fruit of transformants. Thus, antisense gene constructs in plants can be used to block multiple steps in metabolic pathways simultaneously.
Asunto(s)
Hidrolasas de Éster Carboxílico/genética , ADN sin Sentido/farmacología , Poligalacturonasa/genética , Verduras/enzimología , Secuencia de Aminoácidos , Secuencia de Bases , Northern Blotting , Hidrolasas de Éster Carboxílico/metabolismo , Pared Celular/enzimología , Clonación Molecular , ADN Complementario/química , Expresión Génica , Vectores Genéticos , Datos de Secuencia Molecular , Plásmidos , Poligalacturonasa/metabolismo , ARN Complementario/análisis , ARN Mensajero/genética , ARN Mensajero/metabolismo , Alineación de Secuencia , TransfecciónRESUMEN
We isolated a complementary DNA sequence for the enzyme sucrose phosphate synthase (SPS) from maize utilizing a limited amino acid sequence. The 3509-bp cDNA encodes a 1068-amino acid polypeptide. The identity of the cDNA was confirmed by the ability of the cloned sequence to direct sucrose phosphate synthesis in Escherichia coli. Because no plant-specific factors were necessary for enzymatic activity, we can conclude that SPS enzyme activity is conferred by a single gene product. Sequence comparisons showed that SPS is distantly related to the enzyme sucrose synthase. When expressed from a ribulose bisphosphate carboxylase small subunit promoter in transgenic tomatoes, total SPS activity was boosted up to sixfold in leaves and appeared to be physiologically uncoupled from the tomato regulation mechanism. The elevated SPS activity caused a reduction of starch and increase of sucrose in the tomato leaves. This result clearly demonstrates that SPS is involved in the regulation of carbon partitioning in the leaves.
Asunto(s)
Glucosiltransferasas/genética , Plantas/enzimología , Secuencia de Aminoácidos , Secuencia de Bases , Metabolismo de los Hidratos de Carbono , Clonación Molecular , ADN/genética , Expresión Génica , Datos de Secuencia Molecular , Plantas/genética , Plantas/metabolismo , Zea mays/enzimología , Zea mays/genéticaRESUMEN
Improved plant transformation vectors were constructed which utilize the pRiHRI origin of replication for highly stable maintenance in Agrobacterium tumefaciens, the ColE1 origin of replication for high copy maintenance in Escherichia coli, and a gentamycin resistance gene as a strong selectable marker for bacteria. Concise T-DNA elements were engineered with border sequences from the TL-DNA of pTiA6, the Tn5 neomycin phosphotransferase gene (npt II) expressed from either CaMV 35S or mannopine synthase (mas) promoters, and the lac Z' gene segment from pUC18 as a source of unique restriction sites as well as an insertional inactivation marker for cloned DNA. The order of T-DNA components in all vectors is left border, plant marker cassette, lac Z', and right border, respectively. The prototype vector, pCGN1547, was shown to be very stable in A. tumefaciens strain LBA4404 and to act as an efficient donor of T-DNA in tomato transformation experiments. Use of the other vectors is also described.