A non-canonical histone acetyltransferase targets intragenic enhancers and regulates plant architecture

Axillary meristem development determines both plant architecture and crop yield; this critical process is regulated by the TCP transcription factor (TF) family, including the maize TB1 and Arabidopsis BRC1. Studies have shown that both TB1 and AtBRC1 can target the gene body regions of some target genes and activate their expression; however, the regulatory mechanisms remain largely unknown. Here, we show that a cucumber CYC/TB1 homologue, TEN, controls the identity and mobility of tendrils. Through its C-terminus, TEN binds at intragenic enhancers of target genes; its N-terminal domain functions as a novel, non-canonical histone acetyltransferase (HAT) to preferentially act on lysine 56 and 122, of the histone H3 globular domain. This HAT activity is responsible for chromatin loosening and host gene activation. The N-termini of all tested CYC/TB1-like proteins contain an intrinsically disordered region (IDR), and despite their sequence divergence, they have conserved HAT activity. This study discovered a non-canonical class of HATs, and as well, provides a mechanism by which modification at the H3 globular domain is integrated with the transcription process.