Three functionally redundant plant-specific paralogs are core subunits of the SAGA histone acetyltransferase complex in Arabidopsis.

Abstract The SAGA (Spt-Ada-Gcn5 acetyltransferase) complex is an evolutionarily conserved histone acetyltransferase 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 functionally redundant paralogs, SCS1, SCS2A, and SCS2B (SCS1/2A/2B), and a TAF-like subunit, TAFL. Mutations in 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. Furthermore, we demonstrated that SCS1/2A/2B are required for the function of the SAGA complex in histone acetylation, thereby promoting the transcription of development-related genes. These results suggest that SCS1/2A/2B are core subunits of the SAGA complex in Arabidopsis. Compared to SAGA complexes in other eukaryotes, the SAGA complexes in plants have evolved unique features that are necessary for normal growth and development.