LAUSR

The methyltransferase complex (m 6 A writer), which catalyzes the deposition of N 6 -methyladenosine (m 6 A) in mRNAs, is highly conserved across most eukaryotic organisms, but its components and interactions between them are still far from fully understood. Here, using in vivo interaction proteomics, two HAKAI-interacting zinc finger proteins, HIZ1 and HIZ2, are discovered as components of the Arabidopsis m 6 A writer complex. HAKAI is required for the interaction between HIZ1 and MTA (mRNA adenosine methylase A). Whilst HIZ1 knockout plants have normal levels of m 6 A, plants in which it is overexpressed show reduced methylation and decreased lateral root formation. Mutant plants lacking HIZ2 are viable but have an 85% reduction in m 6 A abundance and show severe developmental defects. Our findings suggest that HIZ2 is likely the plant equivalent of ZC3H13 (Flacc) of the metazoan m 6 A-METTL Associated Complex. The components of m 6 A writer and their interactions are still far from fully understood. Here, the authors identify two HAKAI-interacting zinc finger proteins, HIZ1 and HIZ2, as components of the Arabidopsis m 6 A writer complex, and show that hiz2 mutant plants have an 85% reduction in m 6 A abundance and severe developmental defects.