# Identification of the RNA m5C methyltransferase genes in Populus alba × Populus glandulosa and the role of PagTRM4B in wood formation

## TL;DR

This study identifies an RNA methyltransferase gene in poplar and shows its role in wood formation and plant growth.

## Contribution

The study reveals the function of PagTRM4B-a in regulating wood composition and RNA m5C levels in poplar.

## Key findings

- PagTRM4B-a overexpression reduced plant height and stem diameter while altering wood composition.
- Overexpression increased RNA m5C levels and enhanced xylem cell expansion and secondary xylem formation.
- SCW biosynthesis genes were down-regulated in PagTRM4B-a overexpressing transgenic plants.

## Abstract

N5-methylcytosine (m5C) RNA methylation plays an essential role in gene regulation, yet its functions in woody plant development remain poorly understood. This study systematically identified 12 putative tRNA-specific methyltransferase 4 (TRM4) homologs (PagTRM4s) within the P. alba × P. glandulosa genome. Phylogenetic and synteny analyses revealed high evolutionary conservation across Arabidopsis and rice. Structural and domain analyses suggested functional conservation among allelic pairs. Expression profiling showed that PagTRM4B-a maintained stable expression in xylem at different developmental stages. PagTRM4B-a overexpression in poplar resulted in decreased plant height and stem diameter, modified wood composition, and increased RNA m5C levels. Histological analysis showed that overexpression enhanced xylem cell expansion and secondary xylem formation without affecting cambial activity. Moreover, the expression levels of secondary cell wall (SCW) biosynthesis genes were significantly down-regulated in PagTRM4B-a-OE transgenic plants. This study offers new insights into the epigenetic control of secondary growth in trees and highlights PagTRM4B-a as a potential target for influencing wood formation in woody plants.