Arabidopsis INHIBITOR OF GROWTH 2 promotes flowering by regulating NuA4-dependent H4 acetylation levels at <i>FT</i> and <i>SOC1</i>

INHIBITOR OF GROWTH (ING) proteins are chromatin readers that bind trimethylated histone H3 lysine (K) 4 (H3K4me3) marks and associate with either histone acetyltransferase or deacetylase complexes to activate or repress gene transcription, respectively. In plants, there are two types of ING proteins, namely ING1 and ING2. Here, we report that Arabidopsis thaliana ING2 associates with multiple subunits of the histone H4 acetyltransferase complex NuA4, controls genome-wide levels of histone H4 acetylation (H4ac), and regulates different developmental processes, including the initiation of flowering. Our data indicate that ING2 biological functions are largely independent of ING1 activity. We find that ING2 is recruited to the chromatin of key floral integrators, such as FT and SOC1, and is required for their timely activation by modulating histone H4ac levels at these loci. Our observations reveal a genetic interaction between ING2 and genes encoding relevant proteins for H3K4me3 or H2A.Z deposition, suggesting that ING2 might represent a hub for potential crosstalk between histone H4ac and these histone modifications/variants.