Methyltransferase-like (METTL) homologues participate in Nicotiana benthamiana antiviral responses

ABSTRACT

Methyltransferase (MTase) enzymes catalyze the addition of a methyl group to a variety of biological substrates. MTase-like (METTL) proteins are Class I MTases whose enzymatic activities contribute to the epigenetic and epitranscriptomic regulation of multiple cellular processes. N⁶-adenosine methylation (m⁶A) is a common chemical modification of eukaryotic and viral RNA whose abundance is jointly regulated by MTases and METTLs, demethylases, and m⁶A binding proteins. m⁶A affects various cellular processes including RNA degradation, post-transcriptional processing, and antiviral immunity. Here, we used Nicotiana benthamiana and plum pox virus (PPV), an RNA virus of the Potyviridae family, to investigated the roles of MTases in plant–virus interaction. RNA sequencing analysis identified MTase transcripts that are differentially expressed during PPV infection; among these, accumulation of a METTL gene was significantly downregulated. Two N. benthamiana METTL transcripts (NbMETTL1 and NbMETTL2) were cloned and further characterized. Sequence and structural analyses of the two encoded proteins identified a conserved S-adenosyl methionine (SAM) binding domain, showing they are SAM-dependent MTases phylogenetically related to human METTL16 and Arabidopsis thaliana FIONA1. Overexpression of NbMETTL1 and NbMETTL2 caused a decrease of PPV accumulation. In sum, our results indicate that METTL homologues participate in plant antiviral responses.

KEYWORDS:

• Methyltransferase
• METTL
• N⁶-methyladenosine
• antiviral immunity
• Potyviridae
• RNA virus

Acknowledgments

We are grateful to J.A. García (CNB, CSIC, Spain) for materials.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data supporting the findings of this study are available within the article, its supplementary materials or are available from the corresponding authors; the cloned gene sequences are available at NCBI (NbMETTL1, MZ423213; NbMETTL2, GenBank: MT107162). Raw RNA-seq files are available at NCBI under BioProject ID PRJNA953827 (http://www.ncbi.nlm.nih.gov/bioproject/953827).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15592324.2023.2214760.

Additional information

Funding

This study was supported by National Science Foundation of China (grants 31770165 and 31860489 to M.Z.) and Major project of Nature Science Foundation of Inner Mongolia of China (grants 2021ZD06 to M.Z.). F.P. is supported by a “Juan de la Cierva Incorporación” contract (IJC2019-039970-I) from Ministerio de Ciencia e Innovación (Spain), and grants MiniVi (ELIXIR-IIB, Cineca, Italy) and BCV-2023-1-0021 (Red Española de Supercomputación, Spain).