Ectopic expression of the transcriptional regulator and m6A writer complex member HIZ1 impacts development in Arabidopsis.

The Arabidopsis thaliana (Arabidopsis) protein HAKAI-interacting zinc finger protein 1 (HIZ1) is both a transcriptional regulator and a component of the N6-methyladenosine (m6A) writer complex that methylates certain adenosines within mRNA. Unlike other components of this complex, HIZ1 is not expressed constitutively throughout the plant, is not required for m6A deposition, and, when ectopically overexpressed, results in reduced levels of m6A. However, the biological functions of HIZ1 remain unclear. Here, we generated additional HIZ1 constitutive overexpression (HIZ1 OX) lines and selected 8 lines, showing varying levels of expression. These plants exhibited pleiotropic developmental defects, the severity of which correlated with expression level. However, higher levels of HIZ1 overexpression did not reduce m6A levels beyond a 25% decrease, consistent with the complete titration of methylase complex interacting partner(s). Using chromatin immunoprecipitation sequencing (ChIP-seq), we showed that HIZ1 is predominantly associated with predicted gene promoter regions and is significantly enriched on genes whose transcripts in wild-type plants are m6A modified. Our results suggest that constitutive overexpression of HIZ1 promotes vegetative growth and disrupts reproductive growth in Arabidopsis. This likely occurs both through m6A inhibition and transcriptional regulation. Thus, HIZ1 may function in an analogous fashion to the mouse zinc finger protein 217 (ZFP217, human homolog ZNF217), which acts as both a transcriptional regulator and a suppressor of the m6A methylation complex.