Trust in nature

After numerous difficulties, our work, by Liu et al. (2013), on the role of HDA18 in regulating the cellular patterning of Arabidopsis root epidermis,(1) has finally been published. Arabidopsis root epidermis consists of a single layer of cells surrounding a cortex. Cells differentiate into hair (H) or non-hair (N) cells, depending on their positional relationship to underlying cortical cells. Previously, it was demonstrated that a GL2-centered transcriptional factor network, also called pattern genes, determines the fates of the epidermal cells at the N or H positions, and two plasma-membrane-located receptor-like kinase proteins are involved in sensing this positional information.(2)(,)(3) Little is known about how positional information is relayed from the plasma membrane to the nucleus. Eight years ago, we found that the application of the histone deacetylase (HDAC) inhibitor TSA can convert cells at the N position (the epidermal cells over underlying cortical cells) into H cells; H cells are normally differentiated from epidermal cells at the H position (the epidermal cells reside over the intercellular spaces between cortical cells). In the paper reporting this finding,(4) we proposed that histone acetylation is involved in the mediation of positional information. The observation that the mutation of HDA18, a member of the HDAC gene family, produces a similar phenotype to that caused by the application of TSA strongly supported this proposal. However, as no biochemical information about HDA18 was available at the time, to further test our proposal, the top priority for us was to characterize HDA18 and to investigate how this protein is involved in the regulation of the cellular patterning of Arabidopsis root epidermis.