Functional interdependence of N6-methyladenosine methyltransferase complex subunits in Arabidopsis

Maintaining protein homeostasis among different subunits of the m(6) A methyltransferase complex is essential for ensuring proper m(6) A deposition in plants. Addition of N-6-methyladenosine (m(6)A), the most prevalent internal mRNA modification in eukaryotes, is catalyzed by an evolutionarily conserved m(6)A methyltransferase complex. In the model plant Arabidopsis thaliana, the m(6)A methyltransferase complex is composed of 2 core methyltransferases, mRNA adenosine methylase (MTA) and MTB, and several accessory subunits such as FK506-BINDING PROTEIN 12 KD INTERACTING PROTEIN 37KD (FIP37), VIRILIZER (VIR), and HAKAI. It is yet largely unknown whether these accessory subunits influence the functions of MTA and MTB. Herein, I reveal that FIP37 and VIR are indispensable for stabilizing the methyltransferases MTA and MTB, thus functioning as key subunits to maintain the functionality of the m(6)A methyltransferase complex. Furthermore, VIR affects FIP37 and HAKAI protein accumulation, while MTA and MTB mutually influence each other. In contrast, HAKAI has little effect on protein abundance or localization of MTA, MTB, and FIP37. These findings uncover unique functional interdependence at the post-translational level among individual components in the Arabidopsis m(6)A methyltransferase complex, suggesting that maintenance of protein homeostasis among various subunits of the m(6)A methyltransferase complex is essential for maintaining the protein stoichiometry required for the proper function of the m(6)A methyltransferase complex in m(6)A deposition in plants.