VERNALIZATION INSENSITIVE3 (VIN3) induction by vernalization is one of the earliest events in the vernalization response of Arabidopsis (Arabidopsis thaliana). However, the mechanism responsible for vernalization-mediated VIN3 induction is poorly understood. Here, we show that the constitutive repression of VIN3 in the absence of the cold is due to multiple repressive components, including a transposable element-derived sequence, LIKE-HETEROCHROMATIN PROTEIN1 and POLYCOMB REPRESSION COMPLEX2. Furthermore, the full extent of VIN3 induction by vernalization requires activating complex components, including EARLY FLOWERING7 and EARLY FLOWERING IN SHORT DAYS. In addition, we observed dynamic changes in the histone modifications present at VIN3 chromatin during the course of vernalization. Our results show that the induction of VIN3 includes dynamic changes at the level of chromatin triggered by long-term cold exposure.

Proper flowering time is vital for reproductive fitness in flowering plants. In Arabidopsis, vernalization is mediated primarily through the repression of a MADS box transcription factor, FLOWERING LOCUS C (FLC). The induction of a plant homeodomain-containing protein, VERNALIZATION INSENSITIVE 3 (VIN3), by vernalizing cold is required for proper repression of FLC. One of a myriad of changes that occurs after VIN3 is induced is the establishment of FLC chromatin at a mitotically repressed state due to the enrichment of repressive histone modifications. VIN3 induction by cold is the earliest known event during the vernalization response and includes changes in histone modifications at its chromatin. Here, the current understanding of the vernalization-mediated chromatin changes in Arabidopsis is discussed, with a focus on the roles of shared chromatin-modifying machineries in regulating VIN3 and FLC gene family expression during the course of vernalization.

VERNALIZATION INSENSITIVE 3 (VIN3) is required for vernalization-mediated repression of FLOWERING LOCUS C (FLC) in Arabidopsis. The induction of VIN3 by long-term exposure to cold is one of earliest events in vernalization response. However, molecular mechanisms underlying for the VIN3 induction are poorly understood. Recently, we reported that the constitutive repression of VIN3 in the absence of the cold exposure is due to multiple repressive chromatin modifying components, including a transposable element (TE)-derived sequence, LIKE-HETEROCHROMATIN PROTEIN 1 (LHP1) and POLYCOMB REPRESSION COMPLEX 2 (PRC2). In addition, the maximum level of VIN3 induction requires EARLY FLOWERING 7 (ELF7) and EARLY FLOWERING IN SHORDAYS (EFS), which are components of activating chromatin modifying complexes. Furthermore, dynamic changes in histone modifications at VIN3 chromatin are observed during the course of vernalization. Thus, mechanisms underlying the induction of VIN3 include changes at the level of chromatin.