Three Arabidopsis SnRK2 Protein Kinases, SRK2D/SnRK2.2, SRK2E/SnRK2.6/OST1 and SRK2I/SnRK2.3 Involved in ABA-Signaling are Essential for the Control of Seed Development and Dormancy

Abstract

We examined the role of three homologous Arabidopsis ABA-activated SnRK2 protein kinases, SRK2D, SRK2E and SRK2I in seed development and germination. These were mainly expressed in the nucleus during seed development and germination. Unlike srk2d, srk2e and srk2i single and double mutants, the triple mutant was sensitive to desiccation and showed severe growth defects. The triple mutant exhibited a loss of dormancy, vivipary, highly enhanced insensitivity to ABA and elevated seed ABA content relative to wild type plants. The triple mutant had greatly reduced phosphorylation activity of in-gel kinase experiments using bZIP transcription factors including ABI5. Microarray experiments revealed that 48% and 30% of the down-regulated genes in abi5 and abi3 seeds were suppressed in the triple mutant seeds, respectively. Moreover, disruption of the three protein kinases induced global changes in the up-regulation of ABA-repressive gene expression, as well as the down-regulation of ABA-inducible gene expression. These results indicate that these protein kinases are essential for the control of seed development and dormancy through the extensive control of ABA-responsive gene expression.