Accelerated vernalization response by an altered PHD-finger protein in Arabidopsis

Abstract

Vernalization is a response to the winter cold to acquire the competence to flower in next spring. VERNALIZATION INSENSITIVE 3 (VIN3) is a PHD-finger protein that binds to modified histones in vitro. VIN3 is induced by long-term cold and is necessary for Polycomb Repression Complex 2 (PRC2)-mediated tri-methylation of Histone H3 Lysine 27 (H3K27me3) at the FLC locus in Arabidopsis. An alteration in the PHD-finger domain of VIN3 changes the binding specificity of the PHD-finger domain of VIN3 in vitro and results in an accelerated vernalization response in vivo. The acceleration in vernalization response is achieved by increased enrichments of VIN3 and tri-methylation of Histone H3 Lysine 27 (H3K27me3) at the FLC locus without invoking the increased enrichment of Polycomb Repressive Complex 2. This result indicates that the binding specificity of the PHD-finger domain of VIN3 plays a role in mediating a proper vernalization response in Arabidopsis. Furthermore, this work shows a potential that the alteration of PHD-finger domains could be applied to alter various developmental processes in plants.

Keywords: Chromatin; PHD-finger protein; flowering; polycomb Repression Complex 2; vernalization.

Figure 1.

A modified PHD-finger domain of VIN3 (A) Multiple alignments of PHD-finger domains between canonical H3K4me3-binding PHD-finger proteins and VIN3 family proteins. VIN3 family proteins commonly have Serine (S, indicated by _*) at third hydrophobic aromatic ring residue while other known H3K4me3-binding PHD finger domains have conserved Tryptophan (W) residue. Hydrophobic aromatic ring resides forming a binding pocket in PHD finger proteins are indicated by black lined box. A modified VIN3 (VIN3SW), in which Serine (S) at 175 residues is substituted to Tryptophan (W) residue, is shown at the bottom. (B) Schematic cartoon of a hyper-vernalization response mediated by a modified VIN3, VIN3SW. While wild-type Arabidopsis plants are having wild-type VIN3 protein require at least 5–6 weeks to be vernalized (upper), transgenic plants of VIN3SW show accelerated vernalization response compared with wild type, requiring 3–4 weeks to be vernalized (bottom).