It is commonly accepted that the plant pathogens Agrobacterium rhizogenes and Agrobacterium tumefaciens, acting via their T-DNA oncogenes, disturb hormone metabolism or hormone perception pathways in plants, thereby attaining their aim of successful pathogenesis. In this work, we summarize recent data on the A. rhizogenes rolC and rolB oncogenes in comparison to the A. tumefaciens 6b oncogene with respect to their effects on the physiology of transformed cells. The newly discovered functions of the rol genes include the modulation of secondary metabolism, the modulation of levels of intracellular ROS and stress resistance of transformed cells, changed sucrose metabolism, and the inhibition of programmed cell death. We show that the rol genes do not have suppressive effects on plant innate immunity; rather, these genes activate plant defense reactions. The existence of not only the hormone-related mechanism of pathogenicity but also the defense-related mechanism of pathogenicity during plant-Agrobacterium interactions is suggested.
Caffeoylquinic acids are found in artichokes, and they are currently considered important therapeutic or preventive agents for treating Alzheimer's disease and diabetes. We transformed artichoke [the cultivated cardoon or Cynara cardunculus var. altilis DC (Asteraceae)] with the rolC gene, which is a known inducer of secondary metabolism. High-performance liquid chromatography with UV and high-resolution mass spectrometry (HPLC-UV-HRMS) revealed that the predominant metabolites synthesized in the transgenic calli were 1,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, and chlorogenic acid. The rolC-transformed calli contained 1.5% caffeoylquinic acids by dry weight. The overall production of these metabolites was three times higher than that of the corresponding control calli. The enhancing effect of rolC remained stable over long-term cultivation.
The interplay between oncogene expression, ROS production and apoptosis has received a great deal of attention in animal cell biology. Few studies have focused on the role of plant oncogenes in these processes. Plant oncogenes are Agrobacterium T-DNA genes of the plast (RolB) family of eukaryotic regulators.1 During plant infection by the pathogen Agrobacterium rhizogenes, the rolA, rolB and rolC oncogenes are transferred from the bacteria into the plant genome, causing tumor formation and hairy root disease.2 The function of rolB is not restricted to root formation; the gene promotes de novo formation of floral and shoot meristems, induces parthenocarpy, causes a delay in pistil and anther development and modifies the balance between the proliferation of procambial cells and xylem differentiation. 3 The mechanism by which the RolB oncoprotein exerts such varied morphological changes remains unknown.Recently, involvement of the rolB and rolC plant oncogenes in ROS metabolism was revealed. 4,5 Both genes, when expressed in plant cells, decreased intracellular ROS level. The rolB gene acts by inducing upregulation of antioxidant genes, thereby permanently supporting an active anti-oxidative status of transformed cells.5 As ROS perturbations and apoptotic processes are tightly linked, we proposed involvement of the RolB protein in signaling networks regulating PCD in plants. The present investigation was aimed at testing this possibility.The rolB oncogene was previously identified as an important player in ROS metabolism in transformed plant cells. Numerous reports indicate a crucial role for animal oncogenes in apoptotic cell death. Whether plant oncogenes such as rolB can induce programmed cell death (PCD) in transformed plant cells is of particular importance. In this investigation, we used a single-cell assay based on confocal microscopy and fluorescent dyes capable of discriminating between apoptotic and necrotic cells. Our results indicate that the expression of rolB in plant cells was sufficient to decrease the proportion of apoptotic cells in steady-state conditions and diminish the rate of apoptotic cells during induced PCD. These data suggest that plant oncogenes, like animal oncogenes, may be involved in the processes mediating PCD.
Can plant oncogenes inhibit programmed cell death?The rolB oncogene reduces apoptosis-like symptoms in transformed plant cells Necrosis, a rapid form of cell death, is characterized by cytoplasmic swelling, destruction of organelles and disruption of the plasma membrane. 6 Apoptosis is characterized by cell shrinkage, maintenance of organelle integrity and condensation and fragmentation of DNA.6 A distinct type of PCD called apoptosis was originally identified in single cells that were usually surrounded by healthy-looking neighbors. 6 In the present work, we used the terms "PCD" and "apoptosis" interchangeably. Early symptoms of apoptosis, such as nuclear chromatin condensation at the periphery of nucleus and around nucleoli, were studied. To distinguish between necrotic and...
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