# Root tip excision‐induced exodermis lignification impacts lateral root emergence in Brachypodium distachyon

## TL;DR

Stress-induced lignification in the exodermis of Brachypodium distachyon roots affects lateral root emergence, shaping root system architecture.

## Contribution

The study reveals the exodermis as a regulatory hub linking environmental stress to root architecture in grasses.

## Key findings

- Root tip excision reveals two root system architectures: 'pine tree' and 'fishbone'.
- Fishbone phenotype is caused by exodermal lignification affecting lateral root emergence.
- Lignin biosynthesis gene upregulation correlates with the fishbone phenotype.

## Abstract

The mechanisms controlling lateral root emergence in monocots, particularly the role of the exodermis, are poorly understood. We investigated how natural variation in the Brachypodium distachyon stress response shapes root system architecture by modulating cell wall dynamics.We used root tip excision to synchronize lateral root development across natural accessions. The resulting phenotypes were analysed using comparative transcriptomics, biochemical lignin quantification, confocal Raman spectroscopy, and chemical inhibition of lignin biosynthesis.Two distinct root system architectures, ‘pine tree’ and ‘fishbone’, were identified. The ‘fishbone’ phenotype results from an altered lateral emergence caused by a differential lignification intensity of the exodermis. This phenotype was accompanied by the transcriptional upregulation of lignin biosynthesis genes and was partially rescued by treatment with a lignin inhibitor.Stress‐induced exodermal lignification acts as a mechanical ‘brake’ on lateral root emergence. This positions the exodermis as a key regulatory hub that integrates environmental cues with lateral root development to control Root System Architecture plasticity in grasses.

The mechanisms controlling lateral root emergence in monocots, particularly the role of the exodermis, are poorly understood. We investigated how natural variation in the Brachypodium distachyon stress response shapes root system architecture by modulating cell wall dynamics.

We used root tip excision to synchronize lateral root development across natural accessions. The resulting phenotypes were analysed using comparative transcriptomics, biochemical lignin quantification, confocal Raman spectroscopy, and chemical inhibition of lignin biosynthesis.

Two distinct root system architectures, ‘pine tree’ and ‘fishbone’, were identified. The ‘fishbone’ phenotype results from an altered lateral emergence caused by a differential lignification intensity of the exodermis. This phenotype was accompanied by the transcriptional upregulation of lignin biosynthesis genes and was partially rescued by treatment with a lignin inhibitor.

Stress‐induced exodermal lignification acts as a mechanical ‘brake’ on lateral root emergence. This positions the exodermis as a key regulatory hub that integrates environmental cues with lateral root development to control Root System Architecture plasticity in grasses.