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.