Arabidopsis ABA INSENSITIVE4 Regulates Lipid Mobilization in the Embryo and Reveals Repression of Seed Germination by the Endosperm

摘要

Regulation of seed germination requires coordinate action by the embryo and surrounding endosperm. We usednArabidopsis thaliana to establish the relative roles of embryo and endosperm in the control of seed germination andnseedling establishment. We previously showed that endospermic oil reserves are used postgerminatively via gluconeogenesisnto fuel seedling establishment and that lipid breakdown is repressed by abscisic acid (ABA) in embryo but notnendosperm tissues. Here, we use RNA amplification to describe the transcriptome of the endosperm and compare thenhormone responses of endosperm and embryo tissues. We show that the endosperm responds to both ABA and gibberellinnbut that ABA in particular regulates nuclear but not plastid-encoded photosynthetic gene expression in the embryo. We alsonshow that ABA INSENSITIVE4 (ABI4) expression is confined to the embryo, accounts for the major differences in embryonresponse to ABA, and defines a role for ABI4 as a repressor of lipid breakdown. Furthermore, ABI5 expression in thenendosperm defines a second region of altered ABA signaling in the micropylar endosperm cap. Finally, embryo andnendosperm ABA signaling mutants demonstrate the spatial specificity of ABA action in seed germination. We conclude thatnthe single cell endosperm layer plays an active role in the regulation of seed germination in Arabidopsis.