Sense transformation reveals a novel role for class I beta-1, 3-glucanase in tobacco seed germination.
'Coat-enhanced' seed dormancy of many dicotyledonous species, including tobacco, is released during after-ripening. Rupture of the endosperm, which is the limiting step in tobacco seed germination, is preceded by induction of class I beta-1,3-glucanase (betaGLU I) in the micropylar endosperm where the radicle will penetrate. Treating after-ripened tobacco seeds with abscisic acid (ABA) delays endosperm rupture and inhibits betaGLU I induction. Sense transformation with a chimeric ABA-inducible betaGLU I transgene resulted in over-expression of betaGLU I in seeds and promoted endosperm rupture of mature seeds and of ABA-treated after-ripened seeds. Taken together, these results provide direct evidence that betaGLU I contributes to endosperm rupture. Over-expression of betaGLU I during germination also replaced the effects of after-ripening on endosperm rupture. This suggests that regulation of betaGLU I by ABA signalling pathways might have a key role in after-ripening.
Leubner-Metzger
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Friedrich Miescher-Institute, Maulbeerstrasse 66, CH-4058 Basel, Switzerland. leubner@fmi.ch
Meins
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D000040:Abscisic Acid / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D043326:Glucan 1,3-beta-Glucosidase; D010937:Plant Growth Regulators / Q000494:pharmacology; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D012639:Seeds / Q000502:physiology*; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D014170:Transformation, Genetic; D001617:beta-Glucosidase / Q000096:biosynthesis* / Q000235:genetics*
D010937:Plant Growth Regulators; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D000040:Abscisic Acid; D001617:beta-Glucosidase; D043326:Glucan 1,3-beta-Glucosidase