Marking RNA: m(6)A writers, readers, and functions in Arabidopsis

N(6)-methyladenosine (m(6)A) emerges as an important modification in eukaryotic mRNAs. m(6)A has first been reported in 1974, and its functional significance in mammalian gene regulation and importance for proper development have been well established. An arsenal of writer, eraser, and reader proteins accomplish deposition, removal, and interpretation of the m(6)A mark, resulting in dynamic function. This led to the concept of an epitranscriptome, the compendium of RNA species with chemical modification of the nucleobases in the cell, in analogy to the epigenome. While m(6)A has long been known to also exist in plant mRNAs, proteins involved in m(6)A metabolism have only recently been detected by mutant analysis, homology search, and mRNA interactome capture in the reference plant Arabidopsis thaliana. Dysregulation of the m(6)A modification causes severe developmental abnormalities of leaves and roots and altered timing of reproductive development. Furthermore, m(6)A modification affects viral infection. Here, we discuss recent progress in identifying m(6)A sites transcriptome-wide, in identifying the molecular players involved in writing, removing, and reading the mark, and in assigning functions to this RNA modification in A. thaliana. We highlight similarities and differences to m(6)A modification in mammals and provide an outlook on important questions that remain to be addressed.