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Content archived on 2024-04-16

The rol genes as privileged tool to study plant morphogenesis


The primary objective is to produce basic knowledge on the mechanisms by which a variety of signals control growth and cell differentiation. The secondary objective will be to develop tools at cellular and molecular levels to render morphogenetic events accessible to scientific analysis.
This research concerns various aspects and levels of the morphogenesis triggered by the T deoxyribonucleic acid (DNA) genes of Agrobacterium rhizogenes in plants. In the regulation of rolB, its promoter has been shown to be under hormonal, developmental and tissue specific regulation. Detailed histological analysis of GUS gene fusion expression has pointed out a developmental regulation of the rolB promoter which has also been followed during zygotic embryogenesis. The hormonal response of the rolB promoter has also been characterized. The gene has been shown to be auxin inducible and is currently being linked to the developmental control of expression of this gene. Data points to an unexpected role of the 2 thymine adenine thymine adenine (TATA) box in determining tissue specificity and hormonal and developmental regulation of rolB. The role of rolB in triggering rooting is under study and an indoxyl-beta-glucosidase activity has been assigned to rolB. A rolB related auxin binding activity in normal plant cells has been identified. This auxin binding activity is much enhanced in rolB transformed cells where a greatly increased sensitivity to auxin has been measured. rolC is under study and a conjugated cytokinin hydrolase activity assigned to its gene product. The intracellular localization of the rolB and rolC gene products has been defined. Plant genetic mosaics for the expression of a cytokinin gene and plants expressing constitutively rol genes have been constructed and analysed. The characterization of the promoters and the identification of the gene products of open reading frames (ORF) 13 and 14 of the Ri T-DNA is under study. In particular, ORF13 has been shown to be controlled by a wound inducible promoter and to encode for an as yet uncharacterized low molecular weight morphogenic substance. Hormone levels of plants transgenic for prom35S-ORF13 gene fusions are being measured. Characterization has been done at the hystological and ultrastructural level of the developmental and morphological modifications induced by the rol genes A, B and C. Various advanced microanalytical techniques are being utilized to measure hormone levels in districts of plant tissues transformed by the rol genes. These techniques have allowed correlations of alterations of endogenous hormones with specific developmental patterns of transgenic plants. Agrobacterium based transformation techniques have been developed for woody roses in order to exploit the developmental modifications induced by rol genes. Evaluation of the consequences of rol gene expression by a vast morphological and agronomical survey is currently underway. The possible exploitation of the rol-induced morphological alterations in agronomical plants such as alfalfa and kiwi is under study. rolB transgenic kiwi plants show and improved rooting capability, while other interesting modifications are induced by rol genes in alfalfa.
Achieving knowledge and control of growth, development and
morphogenesis of higher plants is among the most formidable
challenges of modern biology and major goals for
agriculture. The molecular events underlying these
physiological processess are however still largely unknown
and not easily approachable. The rol genes of Ri plasmids
affect deeply growth and morphogenetic potential of plant
cells, at least in part by altering the capability to
respond to plant hormones: they represent thus a Privlleged
"window" through which a unique possibility is offered to
investigate on these domains of plant biology and to elaborate powerful tools to manipulate on them. It is the objective of this research proposal to study: i) the regulation of the rol genes, in order to identify DNA regulate sequences and isolate tissue-specific and developmental plant regulatory proteins; ii) the interaction of rol genes with endogeous plant genes, in order to identify and isolate plant genes, in order to identify and isolate plant genes and controlling elements relevant to morphogenesis; iii) the biochemical role of the rol gene products in attering the levels of and the response to hormones, in order to shed light on the molecular mechanisms of hormone response in differentiation; iv) the effects of rol genes on whole plants and cultured tissues (altered hormone balance, morphology, growth pattern and rate, size, juvenility, rooting and regenerative capability etc.)


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Piazzale Aldo Moro 5
00185 ROMA

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Participants (6)