# Transposon-Associated Small RNAs Involved in Plant Defense in Poplar

## TL;DR

This study explores how small RNAs in poplar trees respond to fungal infection, revealing transposon-derived RNAs play a key role in plant defense.

## Contribution

The study identifies transposon-derived small RNAs as significant contributors to plant defense mechanisms during fungal infection in poplar.

## Key findings

- Transposon-derived siRNA clusters significantly increase during fungal infection stages in poplar.
- Populus-specific miRNAs preferentially target NB-LRR genes, suggesting a unique defense strategy.
- sRNAs regulate a large proportion of pathogen genes, especially effector genes during infection phases.

## Abstract

Utilizing high-throughput Illumina sequencing, we examined how small RNA (sRNA) profiles vary in Chinese white poplar (Populus tomentosa) across two pivotal infection stages by the rust fungus Melampsora larici-populina: the biotrophic growth phase (T02; 48 h post infection) and the urediniospore development and dispersal phase (T03; 168 h), both essential for plant colonization and prolonged biotrophic engagement. Far exceeding random expectations, siRNA clusters predominantly arose from transposon regions, with pseudogenes also contributing significantly, and infection-stage-specific variations were notably tied to these transposon-derived siRNAs. As the infection advanced, clusters of 24 nt siRNAs in transposon and intergenic regions exhibited pronounced abundance shifts. An analysis of targets indicated that Populus sRNAs potentially regulate 95% of Melampsora larici-populina genes, with pathogen effector genes showing heightened targeting by sRNAs during the biotrophic and urediniospore phases compared to controls, pointing to selective sRNA-target interactions. In contrast to conserved miRNAs across plant species, Populus-specific miRNAs displayed a markedly greater tendency to target NB-LRR genes. These observations collectively highlight the innovative roles of sRNAs in plant defense, their evolutionary roots, and their dynamic interplay with pathogen coevolution.