Functional analysis of HD2C in Arabidopsis

Ribosome biogenesis is a fundamental process required for all cellular activities. Histone deacetylases play critical roles in many biological processes including transcriptional repression and rDNA silencing. However, their function in pre-rRNA processing remains poorly understood. Here, we discovered a previously uncharacterized role of Arabidopsis histone deacetylase HD2C in pre-rRNA processing via both canonical and non-canonical manners. HD2C interacts with HD2B and forms homo- and/or hetero-oligomers in the nucleolus. Depletion of HD2C and HD2B induces a ribosome biogenesis deficiency morphological phenotype and aberrant accumulation of 18S pre-rRNA intermediates. Our genome-wide analysis revealed that HD2C binds and represses the expression of key genes involved in ribosome biogenesis. Using RNA immunoprecipitation and sequencing, we further uncovered a non-canonical mechanism of HD2C directly associating with pre-rRNA and small nucleolar RNAs to regulate rRNA methylation. Together, this study reveals a multifaceted role of HD2C in ribosome biogenesis and provides mechanistic insights into how histone deacetylases modulate rRNA maturation at both transcriptional and post-transcriptional levels. HD2C binding site were studied with ChIP-seq; Gene expression change in hd2b hd2c double mutant was studied using RNA-seq; H4K16 hyperacetylation site were identtified with H4K16ac ChIP-seq in hd2c mutant; HD2C binding RNAs were identified with HD2C RIP-seq.