Browsing by Author "Hyun, Tae Kyung"

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    Role of α-tocopherol in cellular signaling: α-tocopherol inhibits stress-induced mitogen activated protein kinase activation
    (Springer Science, 2011) Hyun, Tae Kyung; Kumar, Kundan; Rao, Kudupudi Prabhakara; Sinha, Alok Krishna; Roitsch, Thomas
    Tocopherols belong to the plant-derived poly phenolic compounds known for antioxidant functions in plants and animals. Activation of mitogen-activated protein kinases (MAPK) is a common reaction of plant cells in defense-related signal transduction pathways. We report a novel non-antioxidant function of α-tocopherol in higher plants linking the physiological role of tocopherol with stress signalling pathways. Pre-incubation of a low concentration of 50 μM α-tocopherol negatively interferes with MAPK activation in elicitor-treated tobacco BY2 suspension culture cells and wounded tobacco leaves, whereas pre-incubated BY2 cells with α-tocopherol phosphate did not show the inhibitory effect on stimuli-induced MAPK activation. The decreased MAPK activity was neither due to a direct inhibitory effect of α-tocopherol nor due to the induction of an inhibitory or inactivating activity directly affecting MAPK activity. The data support that the target of α-tocopherol negatively regulates an upstream component of the signaling pathways that leads to stress dependent MAPK activation.
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    Tomato mitogen activated protein kinases regulate the expression of extracellular invertase Lin6 in response to stress related stimuli
    (CSIRO Publishing, 2009) Hyun, Tae Kyung; Hoffmann, Anja; Sinha, Alok Krishna; Roitsch, Thomas
    Activation of mitogen-activated protein kinases (MAPKs) is a common reaction of plant cells in defence-related signal transduction pathways. Since the downstream events after the activation of MAPKs are largely unknown in plants, the role of MAPKs in the coordinate regulation of defence reactions and primary carbon metabolism by stress related stimuli has been analysed in tomato (Lycopersicon peruvianum Mill.). Thus, the relationship between MAPK, LpMPK2 and LpMPK3 and extracellular invertase Lin6, as the key enzyme of an apoplasmic phloem unloading pathway, has been analysed. It was observed that the mRNAs of LpMPK3 and Lin6 are sequentially induced by the same set of stress related stimuli, wounding, a fungal elicitor derived from Fusarium oxysporum lycopersici, the endogenous plant derived elicitor PGA and salt stress, while LpMPK2 transcripts are constitutively expressed. In a gain of function approach, a His-tagged version of LpMPK2 and a HA-tagged version of LpMPK3 were transiently and functionally expressed in leaves of transgenic tobacco (Nicotiana tabacum L.) plants expressing the β-glucuronidase reporter gene under control of the Lin6 promoter via agro-infection. The induction of the Lin6 promoter, as revealed by an increase in β-glucuronidase activity after 24 h, was dependent both on the expression and activation of both LpMPK2 and LpMPK3. These data suggest that the induction of extracellular invertase Lin6 by stress-related stimuli requires LpMPK2 and LpMPK3, and thus demonstrate that MAPK signalling might be involved in the regulation of primary carbon metabolism in general and sink metabolism in particular.