Arabidopsis DXO1 activates RNMT1 to methylate the mRNA guanosine cap

Abstract

Eukaryotic messenger RNA (mRNA) typically contains a methylated guanosine (m7G) cap, which mediates major steps of mRNA metabolism. Recently, some RNAs in both prokaryotic and eukaryotic organisms have been found to carry a non-canonical cap such as the NAD cap. Here we report that Arabidopsis DXO family protein AtDXO1, which was previously known to be a decapping enzyme for NAD-capped RNAs (NAD-RNA), is an essential component for m7G capping. AtDXO1 associates with and activates RNA guanosine-7 methyltransferase (AtRNMT1) to catalyze conversion of the guanosine cap to the m7G cap. AtRNMT1 is an essential gene. Partial loss-of-function mutations of AtRNMT1 and knockout mutation of AtDXO1 reduce m7G-capped mRNA but increase G-capped mRNAs, leading to similar pleiotropic phenotypes, whereas overexpression of AtRNMT1 partially restores the atdxo1 phenotypes. This work reveals an important mechanism in m7G capping in plants by which the NAD-RNA decapping enzyme AtDXO1 is required for efficient guanosine cap methylation.

If the 5’ cap fits (wear it) – Non-canonical RNA capping

“…The NAD-capped transcripts were reported to be also spliced, polyadenylated, enriched within the polysomal fraction, and associated with translating ribosomes. Whether NAD-mRNAs are translated in plants, however, remains to be seen [ 96 ]. NAD-RNA is also integral for the response of the plant to the hormone abscisic acid that noticeably changes the NAD-RNA transcriptome and the production of free NAD.…”

DpCoA tagSeq: Barcoding dpCoA-Capped RNA for Direct Nanopore Sequencing via Maleimide-Thiol Reaction

“…The N7-methylguanosine (m 7 G) cap attached to the 5′ end of eukaryotic and specific viral mRNAs is crucial for various biological functions, such as regulating nuclear export, protecting mRNA from degradation by exonucleases, and facilitating translation and 5′-proximal intron excision. − Recent studies have expanded our knowledge of RNA caps, revealing various noncanonical initiation nucleotides (NCINs), including adenosine-containing caps such as nicotinamide adenine dinucleotide (NAD + ), 3′-dephospho-coenzyme A (dpCoA), and flavin adenine dinucleotide (FAD). − In vivo existence of these NCINs has been confirmed in previous research. − In vitro studies also revealed that RNA polymerases (RNAPs) can incorporate the NAD + and dpCoA molecules to the 5′ end of RNAs to produce their capped RNAs, respectively. − …”