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Seed dormancy and ABA metabolism in Arabidopsis and barley: the role of ABA 8'-hydroxylase
Version 2 2023-06-23, 11:05
Version 1 2023-05-26, 11:36
journal contributionposted on 2023-06-23, 11:05 authored by AA Millar, JV Jacobsen, John RossJohn Ross, CA Helliwell, AT Poole, G Scofield, James ReidJames Reid, F Gubler
We have investigated the relationship between seed dormancy and abscisic acid (ABA) metabolism in the monocot barley and the dicot Arabidopsis. Whether dormant (D) or non-dormant (ND), dry seed of Arabidopsis and embryos of dry barley grains all had similarly high levels of ABA. ABA levels decreased rapidly upon imbibition, although they fell further in ND than in D. Gene expression profiles were determined in Arabidopsis for key ABA biosynthetic [the 9-cis epoxycarotenoid dioxygenaseq3gene family] and ABA catabolic [the ABA 8â€²-hydroxylase gene family (CYP707A)] genes. Of these, only the AtCYP707A2 gene was differentially expressed between D and ND seeds, being expressed to a much higher level in ND seeds. Similarly, a barley CYP707 homologue, (HvABA8â€²OH-1) was expressed to a much higher level in embryos from ND grains than from D grains. Consistent with this, in situ hybridization studies showed HvABA8â€²OH-1 mRNA expression was stronger in embryos from ND grains. Surprisingly, the signal was confined in the coleorhiza, suggesting that this tissue plays a key role in dormancy release. Constitutive expression of a CYP707A gene in transgenic Arabidopsis resulted in decreased ABA content in mature dry seeds and a much shorter after-ripening period to overcome dormancy. Conversely, mutating the CYP707A2 gene resulted in seeds that required longer after-ripening to break dormancy. Our results point to a pivotal role for the ABA 8â€²-hydroxylase gene in controlling dormancy and that the action of this enzyme may be confined to a particular organ as in the coleorhiza of cereals. Â© 2006 The Authors.
Publication titleThe Plant Journal
PublisherBlackwell Publishing Ltd.
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