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| Ozone-, ethylene- and pathogen-induced gene regulation: Stilbene biosynthesis in pine |
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D. Ernst, G. Bahnweg, H. Chiron, B. Grimmig, W. Heller, C. Langebartels and H. Sandermann
GSF-Institute of Biochemical Plant Parthology, D-85764 Neuherberg, Germany
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Stilbenes have so far been detected in realtively few plant families where they contribute to the resistance of woody tissues to microbial and herbivore degradation, and act as phytoalexins. In Scots pine trees, the stilbenes piosylvin and pionsylvin 3-O-methylether are known to be the major constitutive phenolic constituents of heartwood and root tissue. In phloem, needles or cell cultures, both compounds are inducible and accumulate upon biotic or abiotic stress by pathogens, UV-C irradiation or ozone. Ozone fumigation with up to 0.3 µl/l enhanced the transcript levels of stilbene synthase (STS) and pinosylvin 3-O-methyltransferase (PMT) in needles but not in healthy phloem. Wounding of stem phloem led to a transient increase in STS and PMT transcripts. This increase was more pronounced in the case of simultaneous fungal inoculation. When applied before wounding or fungal attack, 0.15 µl/l ozone decreased the transient induction of STS and PMT transcripts, but 0.3 µl/l ozone restored and prolonged the induction level over 2 weeks. The present situation is quite unique because the pathway to stilbenes is constitutive in heartwood but is inducible in sapwood, in needles and in cell cultures.
Promoter deletion anaylsis revealed an ozone-responsive region which colud be differentiated from the basal pathogen-responsive, as well as the ethylene-responsive sequence regions. The broad data base now available indicates that the stilbene defence pathway is not turned on by a single switch. An interaction of various cis/trans factors regulates this biosynthetic pathway upon different stresses. Growth and defence in pine rather seem to depend on complex regulatory networks.
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