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The plant-tumorigenic 6b (AK-6b) gene of Agrobacterium tumefaciens strain AKE10 induces morphological alterations to tobacco plants, Nicotiana tabacum. To investigate the molecular mechanisms underlying these processes, we generated transgenic tobacco harboring the AK-6b gene under the control of a dexamethazone-inducible promoter. Upon induction, transgenic tobacco seedlings exhibited distinct
classes of aberrant morphologies, most notably adventitious outgrowths and stunted epicotyls. Histological analysis revealed
massive proliferation and altered venation in the newly established outgrowths. Prominent vascular development suggested that
auxin metabolism or signaling had been altered. Indeed, basipetal auxin transport in the hypocotyls of the transgenic seedlings
was reduced by 50–80%, whereas intracellular auxin contents were only slightly reduced. Analysis of cell extracts by HPLC
revealed a large accumulation of phenolic compounds, including the flavonoid kaempferol-3-rutinoside, in transgenic plants
compared with wild-type seedlings. As some naturally occurring flavonoids have been shown to affect auxin transport, we suggest
that the AK-6b gene expression impairs auxin transport via modulation of phenylpropanoid metabolism, and ultimately results in the observed
morphological alterations.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
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Cell-autonomous cytokinin-independent growth of tobacco cells transformed by Agrobacterium tumefaciens strains lacking the cytokinin biosynthesis gene. 下载免费PDF全文
Mutations at the cytokinin biosynthesis locus (tmr) of Agrobacterium tumefaciens usually result in strains that induce tumors exhibiting the rooty phenotype associated with high auxin-to-cytokinin ratios. However, tobacco (Nicotiana tabacum cv Havana 425) leaf disc explants responded to tmr- mutant strain A356 by producing rapidly growing, unorganized tumors, indicating that these lines can grow in a cytokinin-independent fashion despite the absence of a functional tmr gene. Several methods have been used to characterize the physiological and cellular basis of this phenotype. The results indicate that tmr- tumors have a physiologically distinct mechanism for cytokinin-independent growth in comparison to tumors induced by wild-type bacteria. The cytokinin-independent phenotype of the tmr- transformants appears to be cell autonomous in nature: only the transformed cells and their progeny were capable of cytokinin-independent growth. Specifically, the tmr- tumors did not accumulate cytokinin, and clonal analysis indicated the tmr- transformed cells were not capable of stimulating the growth of neighboring nontransformed cells. Finally, the cytokinin-independent phenotype of the tmr- transformants was shown to be cold sensitive, whereas the wild-type tumors exhibited a cold-resistant cytokinin-independent phenotype. Potential mechanisms for this novel form of cytokinin-independent growth, including the role of the dehydrodiconiferyl alcohol glucosides found in both tumor types, are discussed. 相似文献
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Agrobacteria carrying mutations at the auxin-biosynthesizing loci (iaaH and iaaM of the Ti plasmid) induce shoot-forming tumors on many plant species. In some cases, e.g. Nicotiana glutinosa L., tumors induced by such mutant strains exhibit an unorganized and fully autonomous phenotype. These characteristics are stable in culture at both the tissue and cellular level. We demonstrate that the cytokinin-biosynthesis gene (ipt) of the Ti plasmid is responsble for the induction of both auxin and cytokinin autonomy in N. glutinosa. Cloned cell lines carrying an ipt gene but lacking iaaH and iaaM are capable of accumulating indole-3-acetic acid. Interestingly, non-transformed N. glutinosa tissues exhibit an auxin-requiring phenotype when they are grown on medium supplemented with an exogenous supply of cytokinin. These results strongly indicate that exogenously supplied cytokinin does not mimic all the effects of the expression of the ipt gene in causing the auxin-autonomous growth of N. glutinosa cells.Abbreviations FW
fresh weight
- IAA
indole-3-acetic acid
- I6 Ado
isopentenyladenosine
- kb
kilobase
- MS
Murashige and Skoog (medium)
- NAA
-naphthaleneacetic acid
- NAM
-naphthaleneacetamide
- T-DNA
transferred DNA 相似文献
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Summary Stem pieces and leaf disks of Vitis spp. were cocultured with Agrobacterium tumefaciens strains carrying the UidA (ß-glucuronidase = GUS) gene. The transformation efficiency was highly increased by using a modified T-6b gene (a gene from pTiTm4) which interferes with normal growth and allows regeneration of normal Nicotiana rustica plants (Tinland 1990). The strains first tested on stem segments were subsequently tested in a leaf explant system. On leaves the transformation efficiency of the strains was much lower than with stems. Both the T-6b gene and the hsp 70-T-6b gene (a modified T-6b gene under the control of a heat shock promoter) allowed the initiation of GUS-positive buds.Abbreviations GUS
ß-glucuronidase
- BAP
benzylaminopurine
- X-gluc
5-bromo-4-chloro-3-indolyl glucuronide 相似文献
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Seven natively occurring cytokinins were separated using a high-performanceliquid chromatography system. The analysis was completed in23 min. The applicability of the system is shown in determiningthe cytokinin contents in the plant pathogen Agrobacterium tumefaciensB6, which was found to contain 66 ng of N6-(2-isopentenyl) adenineper g bacteria. High-performance liquid chromatography and gasliquid chromatography are compared and evaluated for cytokinindetermination. (Received May 7, 1976; ) 相似文献
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Erratum
Light-induced expression of ipt from Agrobacterium tumefaciens results in cytokinin accumulation and osmotic stress symptoms in transgenic tobacco 相似文献17.
Cytokinins are plant growth regulators that induce shoot formation, inhibit senescence and root growth. Experiments with hydroponically grown tobacco plants, however, indicated that exogenously applied cytokinin led to the accumulation of proline and osmotin. These responses were also associated with environmental stress reactions, such as salt stress, in many plant species. To test whether increased endogenous cytokinin accumulation led to NaCl stress symptoms, the gene ipt from Agrobacterium tumefaciens, encoding isopentenyl transferase, was transformed into Nicotiana tabacum cv. SR-1 under the control of the light-inducible rbcS-3A promoter from pea. In high light (300 mol PPFD m-2 s-1), ipt mRNA was detected and zeatin/zeatin glucoside levels were 10-fold higher than in control plants or when transformants were grown in low light (30 mol PPFD m-2 s-1). High light treatment was accompanied by increased levels of proline and osmotin when compared to low light grown transformed and untransformed control plants. Elevated in planta cytokinin levels induced responses also stimulated by salt stress, suggesting either common or overlapping signaling pathways are initiated independently by cytokinin and NaCl, setting in motion gene expression normally elicited by developmental processes such as flowering or environmental stress.Abbreviations IPT
isopentenyl, transferase
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rbcS-3A
gene encoding a small subunit protein (SSU) of Rubisco from Pisum sativum
- Rubisco
ribulose 1,5-bisphosphate carboxylase/oxygenase 相似文献
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Relationship between adenylate cytokinin production and Ti plasmid of Agrobacterium tumefaciens 总被引:1,自引:0,他引:1
S Sonoki Y Ohno N Kijima T Hishiyama H Saito T Sugiyama T Hashizume 《Nucleic acids symposium series》1983,(12):111-114
To know whether the tumor-inducing plasmid of Agrobacterium tumefaciens carries genetic information of the biosynthesis of cytokinins, the levels of 6-(3-methyl-2-butenyl-amino)purine (iPAde) and its 4-hydroxy derivative trans-zeatin (trans-Z) and its p-beta-D-ribofuranoside (trans-ZR) produced in media by wild-type virulent strain, plasmid-cured avirulent strain and the deletion mutant were compared. The highest levels of iPAde and trans-Z were found in the culture filtrate of late-log phase growth of plasmid-containing virulent strain, then the levels of iPAde and trans-Z were reduced rapidly at stationary phase. The plasmid-cured avirulent strain and deletion mutant had low levels of iPAde and trans-Z throughout the growth. Results obtained here showed Ti plasmid plays an important role in cytokinin biosynthesis. 相似文献
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Ubiquinone (Coenzyme Q; abbreviation, UQ) acts as a mobile component of the respiratory chain by playing an essential role
in the electron transport system, and has been widely used in pharmaceuticals. The biosynthesis of UQ involves 10 sequential
reactions brought about by various enzymes. In this study we have cloned, expressed the decaprenyl diphosphate synthase, designated
dps gene, from Agrobacterium tumefaciens, and succeeded in detecting UQ-10 in addition to innate UQ-8 in Escherichia coli. Furthermore, the production of UQ-10 was higher than UQ-8. To establish an efficient expression system for UQ-10 production,
we used genes, including ubiC, ubiA, and ubiG involved in UQ biosynthesis in E. coli, to construct a better co-expression system. The expression coupled by dps and ubiCA was effective for increasing UQ-10 production by five times than that by expressing single dps gene in the shake flask culture. To study for a large-scale production of UQ-10 in E. coli, fed-batch fermentations were implemented to achieve a high cell density culture. A cell concentration of 85.40 g/L and 94.58
g/L dry cell weight (DCW), and UQ-10 content of 50.29 mg/L and 45.86 mg/L was obtained after 32.5 h and 27.5 h of cultivation,
subsequent to isopropyl-β-d-thiogalactopy ranoside and lactose induction, respectively. In addition, plasmid stability was maintained at high level throughout
the fermentation. 相似文献
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Bruno Tinland Brigitte Huss François Paulus Géraldine Bonnard Léon Otten 《Molecular & general genetics : MGG》1989,219(1-2):217-224
Summary The T-region located 6b gene of Agrobacterium tumefaciens has been found to interfere with cytokinin effects produced by the cotransferred ipt gene. We have compared the biological activity of three different 6b genes: A-6b from Ach5 (octopine, biotype 1), C-6b from C58 (nopaline, biotype 1) and T-6b from Tm4 (octopine, biotype III) by using different biological assays. Each 6b gene was inserted into a disarmed vector and tested on tobacco stems in coinfection experiments with the Ach5 cytokinin (ipt) gene (A-ipt). A-ipt/C-6b coinfections produced tumours with shoots, A-ipt/A-6b coinfections green tumours and A-ipt/T-6b coinfections tumours with a necrotic surface. The tumour phenotypes obtained were independent of the 6b/A-ipt coinfection ratios, indicating that the strain-specific 6b effects result from the activity of a non-diffusible 6b encoded product. Studies with ipt-less Tm4 mutants showed that 6b genes affect other tumour genes besides the ipt gene and pointed to an influence of T-6b on auxin effects resulting from the Tm4 iaa system. T-iaa/T-6b coinfection experiments showed that T-6b did indeed strongly increase tumour formation by the Tm4 iaa genes. The three 6b genes also have effects which do not require other T-region genes. The complex role of the 6b gene in crown gall induction and Agrobacterium host range will be discussed. 相似文献