The study shows that silencing of NOR2 rRNA genes in Arabidopsis thaliana depends primarily on CHH-context cytosine methylation, particularly mediated by CMT2 and the chromatin remodeler DDM1, rather than CG or CHG methylation. Comparative promoter analysis revealed a prevalence of CHH sites in plant rDNA promoters, explaining why CHH methylation mutants disrupt NOR2 silencing more strongly, while NOR2 loci are hyper‑methylated and more condensed than NOR4.

The study demonstrates that abscisic acid (ABA) accumulates in darkness to suppress cotyledon opening during seedling deetiolation, and that light exposure lifts this repression, enabling cotyledon aperture. Genome‑wide transcriptional and alternative‑splicing changes accompany this process, and the light‑dependent regulation requires the splicing factors RS40 and RS41, whose activity is repressed in the dark.