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Rosalia Deeken - One of the best experts on this subject based on the ideXlab platform.

  • The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Arabidopsis thaliana Crown Galls
    Plant physiology, 2016
    Co-Authors: Rosalia Deeken, Joern Klinkenberg, Stefanie Saupe, Rainer Hedrich, Michael Riedel, Jana Leide, Thomas D. Mueller
    Abstract:

    Nonspecific lipid transfer proteins reversibly bind different types of lipid molecules in a hydrophobic cavity. They facilitate phospholipid transfer between membranes in vitro, play a role in cuticle and possibly in suberin formation, and might be involved in plant pathogen defense signaling. This study focuses on the role of the lipid transfer protein AtLTPI-4 in Crown gall development. Arabidopsis (Arabidopsis thaliana) Crown gall tumors, which develop upon infection with the virulent Agrobacterium tumefaciens strain C58, highly expressed AtLTPI-4. Crown Galls of the atltpI-4 loss-of-function mutant were much smaller compared with those of wild-type plants. The gene expression pattern and localization of the protein to the plasma membrane pointed to a function of AtLTPI-4 in cell wall suberization. Since Arabidopsis Crown Galls are covered by a suberin-containing periderm instead of a cuticle, we analyzed the suberin composition of Crown Galls and found a reduction in the amounts of long-chain fatty acids (C18:0) in the atltpI-4 mutant. To demonstrate the impact of AtLtpI-4 on extracellular lipid composition, we expressed the protein in Arabidopsis epidermis cells. This led to a significant increase in the very-long-chain fatty acids C24 and C26 in the cuticular wax fraction. Homology modeling and lipid-protein-overlay assays showed that AtLtpI-4 protein can bind these very-long-chain fatty acids. Thus, AtLtpI-4 protein may facilitate the transfer of long-chain as well as very-long-chain fatty acids into the apoplast, depending on the cell type in which it is expressed. In Crown Galls, which endogenously express AtLtpI-4, it is involved in suberin formation.

  • grapevine vitis vinifera Crown Galls host distinct microbiota
    Applied and Environmental Microbiology, 2016
    Co-Authors: Hanna Faist, Alexander Keller, Ute Hentschel, Rosalia Deeken
    Abstract:

    ABSTRACT Crown gall disease of grapevine is caused by virulent Agrobacterium strains and establishes a suitable habitat for agrobacteria and, potentially, other bacteria. The microbial community associated with grapevine plants has not been investigated with respect to this disease, which frequently results in monetary losses. This study compares the endophytic microbiota of organs from grapevine plants with or without Crown gall disease and the surrounding vineyard soil over the growing seasons of 1 year. Amplicon-based community profiling revealed that the dominating factor causing differences between the grapevine microbiota is the sample site, not the Crown gall disease. The soil showed the highest microbial diversity, which decreased with the distance from the soil over the root and the graft union of the trunk to the cane. Only the graft union microbiota was significantly affected by Crown gall disease. The bacterial community of graft unions without a Crown gall hosted transient microbiota, with the three most abundant bacterial species changing from season to season. In contrast, graft unions with a Crown gall had a higher species richness, which in every season was dominated by the same three bacteria (Pseudomonas sp., Enterobacteriaceae sp., and Agrobacterium vitis). For in vitro-cultivated grapevine plantlets, A. vitis infection alone was sufficient to cause Crown gall disease. Our data show that microbiota in Crown Galls is more stable over time than microbiota in healthy graft unions and that the microbial community is not essential for Crown gall disease outbreak. IMPORTANCE The characterization of bacterial populations in animal and human diseases using high-throughput deep-sequencing technologies, such as 16S amplicon sequencing, will ideally result in the identification of disease-specific microbiota. We analyzed the microbiota of the Crown gall disease of grapevine, which is caused by infection with the bacterial pathogen Agrobacterium vitis. All other Agrobacterium species were found to be avirulent, even though they lived together with A. vitis in the same Crown gall tumor. As has been reported for human cancer, the Crown gall tumor also hosted opportunistic bacteria that are adapted to the tumor microenvironment. Characterization of the microbiota in various diseases using amplicon sequencing may help in early diagnosis, to serve as a preventative measure of disease in the future.

  • Grapevine (Vitis vinifera) Crown Galls Host Distinct Microbiota.
    Applied and environmental microbiology, 2016
    Co-Authors: Hanna Faist, Alexander Keller, Ute Hentschel, Rosalia Deeken
    Abstract:

    Crown gall disease of grapevine is caused by virulent Agrobacterium strains and establishes a suitable habitat for agrobacteria and, potentially, other bacteria. The microbial community associated with grapevine plants has not been investigated with respect to this disease, which frequently results in monetary losses. This study compares the endophytic microbiota of organs from grapevine plants with or without Crown gall disease and the surrounding vineyard soil over the growing seasons of 1 year. Amplicon-based community profiling revealed that the dominating factor causing differences between the grapevine microbiota is the sample site, not the Crown gall disease. The soil showed the highest microbial diversity, which decreased with the distance from the soil over the root and the graft union of the trunk to the cane. Only the graft union microbiota was significantly affected by Crown gall disease. The bacterial community of graft unions without a Crown gall hosted transient microbiota, with the three most abundant bacterial species changing from season to season. In contrast, graft unions with a Crown gall had a higher species richness, which in every season was dominated by the same three bacteria (Pseudomonas sp., Enterobacteriaceae sp., and Agrobacterium vitis). For in vitro-cultivated grapevine plantlets, A. vitis infection alone was sufficient to cause Crown gall disease. Our data show that microbiota in Crown Galls is more stable over time than microbiota in healthy graft unions and that the microbial community is not essential for Crown gall disease outbreak. The characterization of bacterial populations in animal and human diseases using high-throughput deep-sequencing technologies, such as 16S amplicon sequencing, will ideally result in the identification of disease-specific microbiota. We analyzed the microbiota of the Crown gall disease of grapevine, which is caused by infection with the bacterial pathogen Agrobacterium vitis. All other Agrobacterium species were found to be avirulent, even though they lived together with A. vitis in the same Crown gall tumor. As has been reported for human cancer, the Crown gall tumor also hosted opportunistic bacteria that are adapted to the tumor microenvironment. Characterization of the microbiota in various diseases using amplicon sequencing may help in early diagnosis, to serve as a preventative measure of disease in the future. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

  • RESEARCH ARTICLE Regulation of Oncogene Expression in T-DNA-Transformed Host
    2016
    Co-Authors: Plant Cells, Yi Zhang, Chil-woo Lee, Fabian Imdahl, Veselova Svetlana, Wolfgang Dröge-laser, Rosalia Deeken
    Abstract:

    Virulent Agrobacterium tumefaciens strains integrate their T-DNA into the plant genome where the encoded agrobacterial oncogenes are expressed and cause Crown gall disease. Essential for Crown gall development are IaaH (indole-3-acetamide hydrolase), IaaM (trypto-phan monooxygenase) and Ipt (isopentenyl transferase), which encode enzymes for the biosynthesis of auxin (IaaH, IaaM) and cytokinin (Ipt). Although these oncogenes are well studied as the tumor-inducing principle, nothing is known about the regulation of oncogene expression in plant cells. Our studies show that the intergenic regions (IGRs) between the coding sequences (CDS) of the three oncogenes function as promoters in plant cells. These promoters possess a eukaryotic sequence organization and cis-regulatory elements for the binding of plant transcription factors. WRKY18, WRKY40, WRKY60 and ARF5 were identified as activators of the Ipt promoter whereas IaaH and IaaM is constitutively express-ed and no transcription factor further activates their promoters. Consistent with these re-sults, thewrky triple mutant plants in particular, develops smaller Crown Galls than wild-type and exhibits a reduced Ipt transcription, despite the presence of an intact ARF5 gene

  • DNA Methylation Mediated Control of Gene Expression Is Critical for Development of Crown Gall Tumors
    2016
    Co-Authors: Jochen Gohlke, Rainer Hedrich, Claus-juergen Scholz, Susanne Kneitz, Dana Weber, Joerg Fuchs, Rosalia Deeken
    Abstract:

    Crown gall tumors develop after integration of the T-DNA of virulent Agrobacterium tumefaciens strains into the plant genome. Expression of the T-DNA–encoded oncogenes triggers proliferation and differentiation of transformed plant cells. Crown gall development is known to be accompanied by global changes in transcription, metabolite levels, and physiological processes. High levels of abscisic acid (ABA) in Crown Galls regulate expression of drought stress responsive genes and mediate drought stress acclimation, which is essential for wild-type-like tumor growth. An impact of epigenetic processes such as DNA methylation on Crown gall development has been suggested; however, it has not yet been investigated comprehensively. In this study, the methylation pattern of Arabidopsis thaliana Crown Galls was analyzed on a genome-wide scale as well as at the single gene level. Bisulfite sequencing analysis revealed that the oncogenes Ipt, IaaH, and IaaM were unmethylated in Crown Galls. Nevertheless, the oncogenes were susceptible to siRNA–mediated methylation, which inhibited their expression and subsequently Crown gall growth. Genome arrays, hybridized with methylated DNA obtained by immunoprecipitation, revealed a globally hypermethylated Crown gall genome, while promoters were rather hypomethylated. Mutants with reduced non-CG methylation developed larger tumors than the wild-type controls, indicating that hypermethylation inhibits plant tumor growth. The differential methylation pattern of Crown Galls and the stem tissue from which they originate correlated with transcriptional changes. Genes known to be transcriptionall

Daan A. Weits - One of the best experts on this subject based on the ideXlab platform.

  • Hypoxic Conditions in Crown Galls Induce Plant Anaerobic Responses That Support Tumor Proliferation.
    Frontiers in plant science, 2019
    Co-Authors: Lucy Kerpen, Luca Niccolini, Francesco Licausi, Joost T. Van Dongen, Daan A. Weits
    Abstract:

    Agrobacterium tumefaciens infection of wounded plant tissues causes the formation of Crown gall tumors (Escobar and Dandekar, 2003). Upon infection, genes encoded on the A. tumefaciens tumor inducing plasmid are integrated in the plant genome to induce the biosynthesis of auxin and cytokinin, leading to uncontrolled cell division. Additional sequences present on the bacterial T-DNA encode for opine biosynthesis genes, which induce the production of opines that act as a unique carbon and nitrogen source for Agrobacterium (Escobar and Dandekar, 2003; Guyon et al., 1980). Crown Galls therefore become a very strong sink for photosynthate. Here we found that the increased metabolic demand in Crown Galls causes an increase in oxygen consumption rate, which leads to a steep drop in the internal oxygen concentration. Consistent with this, plant hypoxia-responsive genes were found to be significantly upregulated in Crown Galls compared to uninfected stem tissue. Following this observation, we aimed at understanding whether the low-oxygen response pathway, mediated by group VII ETHYLENE RESPONSE FACTOR (ERF-VII) transcription factors, plays a role in the development of Crown Galls. We found that quintuple knock-out mutants of all ERF-VII members, which are incapable of inducing the hypoxic response, show reduced Crown gall symptoms. Conversely, mutant genotypes characterized by constitutively high levels of hypoxia-associated transcripts, displayed more severe Crown gall symptoms. Based on these results, we concluded that uncontrolled cell proliferation of Crown Galls established hypoxic conditions, thereby requiring adequate anaerobic responses of the plant tissue to support tumor growth.

  • Data_Sheet_1_Hypoxic Conditions in Crown Galls Induce Plant Anaerobic Responses That Support Tumor Proliferation.docx
    2019
    Co-Authors: Lucy Kerpen, Luca Niccolini, Francesco Licausi, Joost T. Van Dongen, Daan A. Weits
    Abstract:

    Agrobacterium tumefaciens infection of wounded plant tissues causes the formation of Crown gall tumors. Upon infection, genes encoded on the A. tumefaciens tumor inducing plasmid are integrated in the plant genome to induce the biosynthesis of auxin and cytokinin, leading to uncontrolled cell division. Additional sequences present on the bacterial T-DNA encode for opine biosynthesis genes, which induce the production of opines that act as a unique carbon and nitrogen source for Agrobacterium. Crown Galls therefore become a very strong sink for photosynthate. Here we found that the increased metabolic demand in Crown Galls causes an increase in oxygen consumption rate, which leads to a steep drop in the internal oxygen concentration. Consistent with this, plant hypoxia-responsive genes were found to be significantly upregulated in Crown Galls compared to uninfected stem tissue. Following this observation, we aimed at understanding whether the low-oxygen response pathway, mediated by group VII ethylene response factor (ERF-VII) transcription factors, plays a role in the development of Crown Galls. We found that quintuple knock-out mutants of all ERF-VII members, which are incapable of inducing the hypoxic response, show reduced Crown gall symptoms. Conversely, mutant genotypes characterized by constitutively high levels of hypoxia-associated transcripts, displayed more severe Crown gall symptoms. Based on these results, we concluded that uncontrolled cell proliferation of Crown Galls established hypoxic conditions, thereby requiring adequate anaerobic responses of the plant tissue to support tumor growth.

  • Hypoxic Conditions in Crown Galls Induce Plant Anaerobic Responses That Support Tumor Proliferation
    Frontiers Media S.A., 2019
    Co-Authors: Lucy Kerpen, Luca Niccolini, Francesco Licausi, Joost T. Van Dongen, Daan A. Weits
    Abstract:

    Agrobacterium tumefaciens infection of wounded plant tissues causes the formation of Crown gall tumors. Upon infection, genes encoded on the A. tumefaciens tumor inducing plasmid are integrated in the plant genome to induce the biosynthesis of auxin and cytokinin, leading to uncontrolled cell division. Additional sequences present on the bacterial T-DNA encode for opine biosynthesis genes, which induce the production of opines that act as a unique carbon and nitrogen source for Agrobacterium. Crown Galls therefore become a very strong sink for photosynthate. Here we found that the increased metabolic demand in Crown Galls causes an increase in oxygen consumption rate, which leads to a steep drop in the internal oxygen concentration. Consistent with this, plant hypoxia-responsive genes were found to be significantly upregulated in Crown Galls compared to uninfected stem tissue. Following this observation, we aimed at understanding whether the low-oxygen response pathway, mediated by group VII ethylene response factor (ERF-VII) transcription factors, plays a role in the development of Crown Galls. We found that quintuple knock-out mutants of all ERF-VII members, which are incapable of inducing the hypoxic response, show reduced Crown gall symptoms. Conversely, mutant genotypes characterized by constitutively high levels of hypoxia-associated transcripts, displayed more severe Crown gall symptoms. Based on these results, we concluded that uncontrolled cell proliferation of Crown Galls established hypoxic conditions, thereby requiring adequate anaerobic responses of the plant tissue to support tumor growth

Chunyan Yan - One of the best experts on this subject based on the ideXlab platform.

  • biotransformation of licochalcone a by transgenic Crown Galls of panax quinquefolium
    Journal of Molecular Catalysis B-enzymatic, 2014
    Co-Authors: Bing Huang, Weihong Zhao, Wenli Wang, Chunyan Yan
    Abstract:

    Licochalcone A, as main constituent of Chinese Gancao (Glycyrrhiza inflate Bat), is responsible for the chemopreventive effect of the herbal. In order to get the bioactive modified molecules of Licochalcone A, it was biotransformed using transgenic Crown Galls of Panax quinquefolium to afford 9 products including a new alkaloid together with 8 known compounds. Their structures were elucidated by physicochemical and spectral methods as: methyl(12S)-1-[(5-formylfuran-2-yl)methyl]-5-oxopyrrolidine-2-carboxylate (1), methyl(12S)-1-[2-(furan-2-yl)-2-oxoethyl]-5-oxopyrrolidine-2-carboxylate (2), 5-hydroxymethyl-2-furfural (3), (S)-methylpyroglutamate (4), 4-hydroxy-2-methoxy-5-(2-methylbut-3-en-2-yl) benzaldehyde (5), 4-hydroxybenzoicacid (6), dibutyl phthalate (7), 3β,6α,12β,25-tetrahydroxy-(20S,24R)-epoxy-dammarane (8), β-sitosterol (9). Among them, compounds 5 and 6 were transformed from Licochalcone A, while 1–4 and 8 were derived from the culture medium stimulated by the substrate. Furthermore, their cancer chemopreventive effect were tested by the assay of NQO1 (NAD(P)H: quinine oxidoreductase 1) inducing activities in Hepa 1c1c cells.

  • Biotransformation of furannoligularenone by transgenic Crown Galls of Panax quinquefolium
    Pharmacognosy magazine, 2012
    Co-Authors: Chunyan Yan, Jue Wang, Guoyan Duan
    Abstract:

    Background: Transgenic plant suspension cultures could be used as an effective tool for the biotransformation of exogenous compounds. Objective: To investigate the biotransformation of furannoligularenone ( 1 ) by transgenic Crown Galls of Panax quinquefolium. Materials and Methods: Compound 1 was administered into the Crown gall cultures and co-cultured for 6 days. The cultures were dried and extracted with methanol for HPLC analyses. The extract was separated on column chromatography, and biotransformation products' structures were elucidated by the physicochemical properties and the data of NMR and MS. Moreover, three flasks were randomly chosen each day to establish time-course during the period for co-culturing . Results: Co-culturing compound 1 with Crown Galls yielded two compounds, 3-oxo-eremophila-1,7(11)-dien-12,8-olide ( 2 ) and 3-oxo-8-hydroxy-eremophila-1,7(11)-dien-12,8-olide ( 3 ), which were obtained by biotransformation using P. quinquefolium Crown Galls for the first time. Time-course investigation revealed that the mole conversion ratio reached the highest level of 45.5% and 33.9% on fourth and fifth day after substrate administration, respectively. Furthermore, a proposal biosynthesis pathway was given from compound 1 to compounds 2 and 3 . Conclusion: This was the first example of compound 1 being successfully converted into compounds 2 and 3 by transgenic Crown Galls of P. quinquefolium.

  • biotransformation of eugenol by suspension cultures of transgenic Crown Galls of panax quinquefolium and suspension cultures of nicotiana tabacum
    World Journal of Microbiology & Biotechnology, 2010
    Co-Authors: Lin Yang, Jianhua Zhu, Chunyan Yan, Liyan Song
    Abstract:

    The biocatalytic ability of transgenic Crown Galls of Panax quinquefolium was evaluated by using eugenol (1) as a substrate and suspension cultures of Nicotiana tabacum as control system. Three biotransformed products, namely: 2-methoxy-4-(2-propenyl)phenyl-O-β-d-glucopyranoside (2, 67.11%), 2-methoxy-4-(2-propenyl)phenyl-O-β-d-glucopyranosyl (6′ → 1″)-β-d-xylopyranoside (3, 2.85%) and methyl eugenol (4, 14.30%) were obtained after 5 days of administration of eugenol to the suspension cultures of transgenic Crown Galls of P. quinquefolium. In contrast, only one product, compound 2 (15.41%), was obtained in suspension cultures of N. tabacum after 5 days of incubation. The results indicated that the glycosylation ability of transgenic Crown Galls of P. quinquefolium was much higher than that of the cultured cells of N. tabacum.

  • Biotransformation of Paeonol and Emodin by Transgenic Crown Galls of Panax quinquefolium
    Applied biochemistry and biotechnology, 2009
    Co-Authors: W. L., Jianhua Zhu, Chunyan Yan, G. Y. Duan
    Abstract:

    Two aromatic substrates, paeonol (1) and emodin (2), were biotransformed by using transgenic Crown Galls of Panax quinquefolium. Four biotransformed products (3–6) were isolated and identified by physicochemical and spectral methods. A β-glucoside (3, 73.2% of biotransformation yield) and a 1-(2,4-dimethoxyphenyl)- ethanone (4, 8.03%) were isolated from the suspension cultures after 7-day incubation of substrate 1. Upon administration of substrate 2, another β-glucoside [emodin-6-O-β-d-glucopyranoside (5), 19.2%] and a hydroxylated derivative, citreorosein (6, 54.6%), were also obtained. The results demonstrate that transgenic Crown Galls of P. quinquefolium have the capacities to catalyze glycosylation, hydroxylation, and methylation reactions in the plant cells on those aromatic compounds.

Sebahattin Ozcan - One of the best experts on this subject based on the ideXlab platform.

  • in vitro Crown Galls induced by agrobacterium tumefaciens strain a281 ptibo542 in trigonella foenum graecum
    Biologia Plantarum, 2004
    Co-Authors: Khalid Mahmood Khawar, Selma Gulbittionarici, Sati Cocu, Semiha Erisen, Cengiz Sancak, Sebahattin Ozcan
    Abstract:

    Transformation of fenugreek (Trigonella foenumgraecum) was carried out with A281 oncogenic strain of Agrobacterium tumefaciens using root, cotyledon and hypocotyl explants excised from 1-week-old seedlings, which showed that the plant was highly susceptible to transformation. Tumors (calli) were selected on 50 mg dm−3 kanamycin. They were analyzed for β-glucuronidase (GUS) expression. Presence of uidA (gus) gene, was confirmed by polymerase chain reaction (PCR) amplification.

  • in vitro induction of Crown Galls by agrobacterium tumefaciens super virulent strain a281 ptibo 542 in salvia sclarea and s pratense
    Biotechnology & Biotechnological Equipment, 2003
    Co-Authors: Khalid Mahmood Khawar, T Unver, Sebahattin Ozcan
    Abstract:

    ABSTRACTSalvia sclareae and S. pratense are important medicinal plants. The application of genetic engineering to these important crops should allow incorporation of some traits like insect and herbicide resistance. Co-cultivation experiments with A281 strain of Agrobacterium tumefaciens using leaf explants excised from 35 days old seedlings of both species showed that these were highly susceptible to transformation. Moreover, the strain A281 resulted in development of shooty tumors in S. sclarea and rooty tumors in S. pratense, which were selected on MS medium containing 50 mg/1 kanamycin. All of them were GUS positive.

  • in vitro induction of Crown Galls by agrobacterium tumefaciens super virulent strain a281 ptibo 542 in lentil lens culinaris medik
    Turkish Journal of Botany, 2002
    Co-Authors: Khalid Mahmood Khawar, Sebahattin Ozcan
    Abstract:

    Twenty-one genotypes of lentils (Lens culinaris Medik.), obtained from different sources in Turkey and Pakistan, were included in the study. Seeds were germinated in MS medium for 6-10 days with a 16 h photoperiod at 24°C, from which leaf and stem explants were isolated for inoculation with super virulent strain A281 (pTiBo 542) :: pBI121.1 agropine/mannopine type of Agrobacterium tumefaciens. The binary plasmid pBI121.1 carried a GUS gene directed by CaMV 35S promoter in order to confirm transformation by GUS expression. Parameters recorded include percentage of tumour formation, tumour diameter, and tumour weight. Pul 11, Kislik Yesil 21, Akm 565 were best when leaf explants were used, whereas Kirmizi 51, Malazgirt, Akm 49 and Akm 196 were best when stem explants were used in tumour induction. Pul 11, Kirmizi 51, Ill 62, Emre 20, Malazgirt, Akm 565, Akm 49, Akm 62, Akm 196, Akm 261, Akm 263, Akm 302 and Akm 362 formed tumours on both leaf and stem explants. Four cultivars, namely, Masoor 85, Masoor 93, Akm 247 and Akm 258, did not induce tumours on leaf explants, whereas six genotypes, namely, Sazak 91, Kayi 91, Masoor 85, Masoor 93 Akm 247 and Akm 260 had no tumours when stem explants were used. Tumour induction was also confirmed by histochemical GUS analysis.

Harry J Klee - One of the best experts on this subject based on the ideXlab platform.

  • the never ripe mutant provides evidence that tumor induced ethylene controls the morphogenesis of agrobacterium tumefaciens induced Crown Galls on tomato stems
    Plant Physiology, 1998
    Co-Authors: Roni Aloni, Asnat Wolf, Pua Feigenbaum, Adi Avni, Harry J Klee
    Abstract:

    We confirm the hypothesis that Agrobacterium tumefaciens-induced Galls produce ethylene that controls vessel differentiation in the host stem of tomato (Lycopersicon esculentum Mill.). Using an ethylene-insensitive mutant, Never ripe (Nr), and its isogenic wild-type parent we show that infection by A. tumefaciens results in high rates of ethylene evolution from the developing Crown Galls. Ethylene evolution from isolated internodes carrying Galls was up to 50-fold greater than from isolated internodes of control plants when measured 21 and 28 d after infection. Tumor-induced ethylene substantially decreased vessel diameter in the host tissues beside the tumor in wild-type stems but had a very limited effect in the Nr stems. Ethylene promoted the typical unorganized callus shape of the gall, which maximized the tumor surface in wild-type stems, whereas the Galls on the Nr stems had a smooth surface. The combination of decreased vessel diameter in the host and increased tumor surface ensured water-supply priority to the growing gall over the host shoot. These results indicate that in addition to the well-defined roles of auxin and cytokinin, there is a critical role for ethylene in determining Crown-gall morphogenesis.