The Arabidopsis spliceosomal protein SmEb modulates ABA responses by maintaining proper alternative splicing of HAB1.

Abscisic acid (ABA) signaling is critical for seed germination and abiotic stress responses in terrestrial plants. Pre-mRNA splicing is known to regulate ABA signaling. However, the involvement of canonical spliceosomal components in regulating ABA signaling is poorly understood. Here, we show that the spliceosome component Sm core protein SmEb plays an important role in ABA signaling. SmEb expression is up-regulated by ABA treatment, and analysis of Arabidopsis smeb mutant plants suggest that SmEb modulates the alternative splicing of the ABA signaling component HAB1 by enhancing the HAB1.1 splicing variant while repressing HAB1.2. Overexpression of HAB1.1 but not HAB1.2 rescues the ABA-hypersensitive phenotype of smeb mutants. Mutations in the transcription factor ABI3, 4, or 5 also reduce the ABA hypersensitivity of smeb mutants during seed germination. Our results show that the spliceosomal component SmEb plays an important role in ABA regulation of seed germination and early seedling development.