# DNA Methylation Fine-Tunes Light- and Hormone-Responsive Growth Plasticity in Arabidopsis Seedlings

## TL;DR

This study shows how DNA methylation in Arabidopsis seedlings helps regulate growth in response to light and hormones.

## Contribution

The study reveals how DNA methylation integrates environmental and hormonal signals to fine-tune seedling growth.

## Key findings

- DNA methylation mutants showed altered hypocotyl elongation and cotyledon expansion under specific light conditions.
- Exogenous auxin and gibberellin treatments revealed genotype-specific growth responses linked to methylation status.
- Methylation affects gene expression in auxin transport, signaling, and light regulation pathways.

## Abstract

DNA methylation regulates plant growth by modulating gene expression; however, its contribution to hormone responsiveness and photomorphogenesis remains only partially understood. We examined Arabidopsis thaliana DNA methylation mutants met1 and drm1, drm2, and cmt3 (ddc) under defined light regimes and following exogenous treatments with auxin, gibberellin, and the auxin transport inhibitor TIBA. Hypocotyl elongation and cotyledon expansion exhibited strong light dependency across all genotypes, with met1 seedlings developing a consistently reduced cotyledon area and ddc seedlings displaying impaired hypocotyl elongation under specific light qualities. Exogenous auxin inhibited growth in all genotypes, whereas GA3 promoted elongation in hypocotyls and roots (by approximately 75–80% and 15–35%, respectively, in Col0 and met1), with ddc exhibiting delayed and non-linear dose-dependent sensitivity. Quantitative RT–PCR analysis revealed differential expression of genes involved in auxin transport (PIN1, PIN3, PIN7), auxin signalling (ARF7, IAA3, LAX3), circadian regulation (TOC1, LHY, CCA1), and light signalling (PIFs, HY5, HYH), supporting a link between DNA methylation status and coordinated regulation of hormone-, light-, and clock-controlled transcriptional networks. Together, these findings demonstrate that MET1- and DRM/CMT-dependent methylation pathways integrate epigenetic regulation with environmental and hormonal cues, modulating the intensity, timing, and organ specificity of growth responses, thereby fine-tuning growth plasticity during early Arabidopsis seedling development.