show Abstracthide AbstractLoss of DNA methylation is traditionally associated with transcriptional up-regulation of transposable elements. Here we describe for the first time expression changes upon loss of DNA methylation in diatoms using Phaeodactylum tricornutum as a model species. The loss of DNA methylation was obtained by generation of DNMT5 KOs, a divergent DNMT with SNF-like domains. Expression analysis confirm the loss of DNA methylation is associated with de-repression of transposable elements in Phaeodactylum tricornutum with indirect effects on protein coding genes. Overall design: 3 conditions - 2 independent DNMT5:KOs -> DNMT5:KO line M23 ; DNMT5:KO line M25 + 1 reference strain "WT" Pt18.6. 2 replicates per condition.