Conserved and unique features of the SAGA complex in plants [ChIP-seq]

The SAGA (Spt-Ada-Gcn5 acetyltransferase) complex is an evolutionarily conserved, multifunctional co-activator complex, which has a critical role in histone acetylation, gene expression, and various developmental processes in eukaryotes. However, little is known about the composition and function of the SAGA complex in plants. Here, we found that the SAGA complex in Arabidopsis thaliana contains not only conserved subunits and but also four plant-specific subunits, including three homologous subunits, SCS1, SCS2A, and SCS2B (SCS1/2A/2B), and a TAF-like subunit, TAFL. We also found that a series of SAGA subunits are shared in yeast and/or metazoans but are absent in Arabidopsis. Mutations in the unique SAGA subunits SCS1/2A/2B lead to defective phenotypes similar to those caused by mutations in the conserved SAGA subunits HAG1 and ADA2B; these defective phenotypes include delayed juvenile-to-adult phase transition, late flowering, and increased trichome density. SCS1/2A/2B function in the SAGA complex to promote the transcription of development-related genes by facilitating histone H3 acetylation. The results suggest that, compared to SAGA complexes in other eukaryotes, the SAGA complex in plants has evolved unique features that are necessary for normal growth and development. Overall design: Examination of H3K9Ac levels in wild type and three mutants.