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Seed dormancy and ABA metabolism in Arabidopsis and barley: the role of ABA 8¢-hydroxylase


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Millar, AA, Jacobsen, JV, Ross, JJ, Helliwell, CA, Poole, AT, Scofield, G, Reid, JB and Gubler, F 2006 , 'Seed dormancy and ABA metabolism in Arabidopsis and barley: the role of ABA 8¢-hydroxylase' , The Plant Journal, vol. 45 , pp. 942-954 , doi: 10.1111/j.1365-313X.2006.02659.x.

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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 dioxygenase gene family] and ABA catabolic [the ABA 8¢-
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, (HvABA8¢OH-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 HvABA8¢OH-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 afterripening
to break dormancy. Our results point to a pivotal role for the ABA 8¢-hydroxylase gene in controlling
dormancy and that the action of this enzyme may be confined to a particular organ as in the coleorhiza of

Item Type: Article
Authors/Creators:Millar, AA and Jacobsen, JV and Ross, JJ and Helliwell, CA and Poole, AT and Scofield, G and Reid, JB and Gubler, F
Journal or Publication Title: The Plant Journal
ISSN: 0960-7412
DOI / ID Number: 10.1111/j.1365-313X.2006.02659.x
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