| Summary: | <p>Abstract</p> <p>Background</p> <p>Imbibed seeds integrate environmental and endogenous signals to break dormancy and initiate growth under optimal conditions. Seed maturation plays an important role in determining the survival of germinating seeds, for example one of the roles of dormancy is to stagger germination to prevent mass growth under suboptimal conditions. The B3-domain transcription factor FUSCA3 (FUS3) is a master regulator of seed development and an important node in hormonal interaction networks in <it>Arabidopsis thaliana</it>. Its function has been mainly characterized during embryonic development, where <it>FUS3 </it>is highly expressed to promote seed maturation and dormancy by regulating ABA/GA levels.</p> <p>Results</p> <p>In this study, we present evidence for a role of <it>FUS3 </it>in delaying seed germination at supraoptimal temperatures that would be lethal for the developing seedlings. During seed imbibition at supraoptimal temperature, the <it>FUS3 </it>promoter is reactivated and induces <it>de novo </it>synthesis of <it>FUS3 </it>mRNA, followed by FUS3 protein accumulation. Genetic analysis shows that <it>FUS3 </it>contributes to the delay of seed germination at high temperature. Unlike WT, seeds overexpressing <it>FUS3 </it>(<it>ML1:FUS3-GFP</it>) during imbibition are hypersensitive to high temperature and do not germinate, however, they can fully germinate after recovery at control temperature reaching 90% seedling survival. <it>ML1:FUS3-GFP </it>hypersensitivity to high temperature can be partly recovered in the presence of fluridone, an inhibitor of ABA biosynthesis, suggesting this hypersensitivity is due in part to higher ABA level in this mutant. Transcriptomic analysis shows that WT seeds imbibed at supraoptimal temperature activate seed-specific genes and ABA biosynthetic and signaling genes, while inhibiting genes that promote germination and growth, such as GA biosynthetic and signaling genes.</p> <p>Conclusion</p> <p>In this study, we have uncovered a novel function for the master regulator of seed maturation, <it>FUS3</it>, in delaying germination at supraoptimal temperature. Physiologically, this is important since delaying germination has a protective role at high temperature. Transcriptomic analysis of seeds imbibed at supraoptimal temperature reveal that a complex program is in place, which involves not only the regulation of heat and dehydration response genes to adjust cellular functions, but also the activation of seed-specific programs and the inhibition of germination-promoting programs to delay germination.</p>
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