Plant Elongator regulates auxin-related genes during RNA polymerase II transcription elongation

Abstract

In eukaryotes, transcription of protein-encoding genes is strongly regulated by posttranslational modifications of histones that affect the accessibility of the DNA by RNA polymerase II (RNAPII). The Elongator complex was originally identified in yeast as a histone acetyltransferase (HAT) complex that activates RNAPII-mediated transcription. In Arabidopsis thaliana, the Elongator mutants elo1, elo2, and elo3 with decreased leaf and primary root growth due to reduced cell proliferation identified homologs of components of the yeast Elongator complex, Elp4, Elp1, and Elp3, respectively. Here we show that the Elongator complex was purified from plant cell cultures as a six-component complex. The role of plant Elongator in transcription elongation was supported by colocalization of the HAT enzyme, ELO3, with euchromatin and the phosphorylated form of RNAPII, and reduced histone H3 lysine 14 acetylation at the coding region of the SHORT HYPOCOTYL 2 auxin repressor and the LAX2 auxin influx carrier gene with reduced expression levels in the elo3 mutant. Additional auxin-related genes were down-regulated in the transcriptome of elo mutants but not targeted by the Elongator HAT activity showing specificity in target gene selection. Biological relevance was apparent by auxin-related phenotypes and marker gene analysis. Ethylene and jasmonic acid signaling and abiotic stress responses were up-regulated in the elo transcriptome and might contribute to the pleiotropic elo phenotype. Thus, although the structure of Elongator and its substrate are conserved, target gene selection has diverged, showing that auxin signaling and influx are under chromatin control.