RNA chemical modification of m<sup>6</sup>A in plants

Abstract

<p indent="0mm">N⁶-methyladenosine (m⁶A) is the most prevalent methylation modification form of eukaryotic messenger RNAs (mRNA). In plants, m⁶A participates in a variety of biological processes by affecting mRNA alternative polyadenylation, stability, and translation. In existing research, the absence of some methyltransferase complexes, such as methyltransferase A (MTA), methyltransferase B (MTB), FKBP12 interacting protein (FIP37), and virilizer (VIR), in plants causes embryonic lethality. Lowering gene expression levels of different methyltransferase components will cause severely hindered growth and development, such as growth retardation, over-proliferation of shoot apical meristem, aberrant gravity response, abnormal vascular tissue development, etc. Loss of demethylase AlkB homolog 10B (ALKBH10B) increases m⁶A modification levels of FLOWERING LOCUS T (<italic>FT</italic>), SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 3 (<italic>SPL3</italic>), and <italic>SPL9</italic>, lowering their stability, which leads to delayed flowering. The absence of AlkB homolog 9B (ALKBH9B) can increase the genomic m⁶A modification level of the alfalfa mosaic virus (AMV), weakening its infection capacity to plants. RNA binding proteins are mainly proteins with the YTH-domain. The evolutionarily conserved c-terminal region (ECT) represents main RNA binding proteins in plants. ECT2, ECT3, and ECT4, three kinds of ECTs, affect trichome branch numbers, precise leaf formation timing, and leaf morphology. Furthermore, the longer isoform of CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR 30 (CPSF30-L) which has mRNA binding function influences processes of polyadenylation site selection and phase separation. In addition to these features, these binding proteins are quite likely to be involved in plant response processes to adversity stress.<bold> </bold>Through the comprehensive analysis of existing studies, we considered that m⁶A is mainly enriched in the 3′ untranslated regions (3′UTR) region nearby the stop codon of plant mRNAs. As for the m⁶A modification enriched in the 5′ untranslated regions (5′UTR) region may be relevant to the higher abundance of chloroplast-related genes. The whole plant m⁶A-seq results show that RR[A]CH is a main m⁶A motif of plants. Sequencing of m⁶A at specific tissue sites or the sequence recognized by the binding protein indicated that UGU[A]Y is a plant-specific motif. As for the divergences in existing research about how m⁶A influences plant mRNA stability, we supposed that the existence of m⁶A is positively correlated with mRNA stability. However, there would be a negative correlation between m⁶A level and mRNA stability when m⁶A exists. In this article, we reviewed the research progress of plant m⁶A on three aspects, including m⁶A modification-related regulatory proteins and their functions, m⁶A position distribution and its motif characteristics, and the molecular mechanism of m⁶A regulation. Finally, we summarized the high-valued research emphasis and directions of m⁶A in plants.