Functional studies of class II and IV histone deacetylases in Arabidopsis
Date Issued
2010
Date
2010
Author(s)
Velasco Alinsug, Malona
Abstract
Histone acetylation has been known to induce an open chromatin configuration leading to gene transcription while deacetylation stimulates chromatin condensation triggering transcriptional quiescence. In Arabidopsis, there are 12 histone deacetylases classified under the RPD3/HDA1 superfamily which is further subdivided into 3 distinct classes namely Class I, II, and IV. Among these 12 HDAs, 4 remains to be unclassified namely HDA8, HDA10, HDA14, and HDA17. Based on our phylogenetic analyses, HDA10 and HDA17 share high sequence homology to members of the Class I HDAs while HDA8 and HDA14 exhibited higher similarity with HDA5, HDA15, and HDA18, members of the Class II HDAs, based on their conserved histone deacetylase domains.
Moreover, Class II histone deacetylases in humans and other model organisms undergo nucleocytoplasmic shuttling. This unique functional regulatory mechanism has been well studied especially in mammalian organisms except in plant systems. In this study, we have paved the baseline evidence for the cytoplasmic and partial nuclear localization of Class II & IV HDAs. HDA15, in particular, localizes in the nucleolus in the presence of light and eventually transports into the cytoplasm upon dark treatment. This data provides the final piece of the puzzle concluding that nucleocytoplasmic shuttling, indeed, is a hallmark for all eukaryotic Class II histone deacetylases.
Except for HDA18 which plays a role in root epidermal patterning, there are no other studies elaborating on any of the repressive functions of Class II & IV histone deacetylases in plants. Based on the functional genetic analyses of HDA2 and HDA15 using T-DNA knock out, RNAi, and overexpression plants, HDA2 and HDA15 play positive regulatory roles in photomorphogenesis repressing the expression of PIFs and COP1. The findings of this research fine tune our prior understanding of the role of histone modifications in light-regulated gene expression such that light not only induces the acetylation of key positive regulators of photomorphogenesis but also may render the simultaneous repression and inactivation of COP1 and PIFs via deacetylation. This concerted enzymatic activity of histone acetyltransferases and deacetylases in the light signaling pathway may take a colossal hold on the master switches controlling its transcriptional regulation.
Subjects
histone deacetylase
nucleocytoplasmic shuttling
photomorphogenesis
Type
thesis
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