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

Abstract

We examined the role of three redundant Arabidopsis ABA-activated SnRK2 protein kinases, SRK2D, SRK2E, and SRK2I for seed development and germination. During seed development and germination, these proteins are expressed in nucleus. A srk2d srk2e srk2i mutant was sensitive to dehydration and showed severe growth defects during silique and seed development. During seed germination, the triple mutant exhibited a hyper ABA-insensitive phenotype, which was more pronounced than in any single or double mutants and any abi mutants. A viviparous phenotype in the triple mutant was also observed. In-gel kinase experiments showed that the srk2d srk2e srk2i mutant had greatly reduced 42-kD kinase activity, resulting in diminished phosphorylation of ABI5. Transcriptome analyses suggest that SRK2D, SRK2E, and SRK2I protein kinases might control seed maturation and germination through the control of gene expression extensively.