Plasticity of DNA methylation and gene expression under zinc deficiency in Arabidopsis roots

DNA methylation is a heritable chromatin modification that maintains chromosome stability, regulates transposon silencing and appears to be involved in gene expression in response to environmental conditions. Environmental stress alters DNA methylation patterns that are correlated with gene expression differences. Here, genome-wide differential DNA methylation was identified upon prolonged zinc (Zn) deficiency, leading to hypo- and hypermethylated chromosomal regions. Preferential CpG methylation changes occurred in gene promoters and gene bodies, but did not overlap with transcriptional start sites. Methylation changes were also prominent in transposable elements. In contrast, non-CpG methylation differences were exclusively found in promoters of protein-coding genes and in transposable elements. Strongly Zn deficiency-induced genes and their promoters were mostly non-methylated, irrespective of Zn supply. Differential DNA methylation in the CpG and CHG, but not in the CHH context, was found close to a few up-regulated Zn deficiency genes. However, the transcriptional Zn deficiency response in roots appeared little correlated with associated DNA methylation changes in promoters or gene bodies. Furthermore, under Zn deficiency, developmental defects were identified in an Arabidopsis mutant lacking non-CpG methylation. The root methylome thus responds specifically to a micronutrient deficiency and is important for efficient Zn utilization at low availability, but the relationship of differential methylation and differentially expressed genes is surprisingly poor.