Phosphorylation of Histone H2A at Serine 95: A Plant-Specific Mark Involved in Flowering Time Regulation and H2A.Z Deposition

Abstract

Phosphorylation of histone H3 affects transcription, chromatin condensation, and chromosome segregation. However, the role of phosphorylation of histone H2A remains unclear. Here, we found that Arabidopsis thaliana MUT9P-LIKE-KINASE (MLK4) phosphorylates histone H2A on serine 95, a plant-specific modification in the histone core domain. Mutations in MLK4 caused late flowering under long-day conditions but no notable phenotype under short days. MLK4 interacts with CIRCADIAN CLOCK ASSOCIATED1 (CCA1), which allows MLK4 to bind to the GIGANTEA (GI) promoter. CCA1 interacts with YAF9a, a co-subunit of the Swi2/Snf2-related ATPase (SWR1) and NuA4 complexes, which are responsible for incorporating the histone variant H2A.Z into chromatin and histone H4 acetylase activity, respectively. Importantly, loss of MLK4 function led to delayed flowering by decreasing phosphorylation of H2A serine 95, along with attenuated accumulation of H2A.Z and the acetylation of H4 at GI, thus reducing GI expression. Together, our results provide insight into how phosphorylation of H2A serine 95 promotes flowering time and suggest that phosphorylation of H2A serine 95 modulated by MLK4 is required for the regulation of flowering time and is involved in deposition of the histone variant H2A.Z and H4 acetylation in Arabidopsis.

SIP1 participates in regulation of flowering time in rice by recruiting OsTrx1 to Ehd1

“…The transcription factor SUF4 interacts with MOS1 (MODIFIER OF snc1) to regulate the flowering time (Li et al ., 2010; Bao et al ., 2014). Recent results have supported the idea that transcriptional factors are critical for histone phosphorylation to regulate flowering time and hypocotyl elongation in Arabidopsis (Su et al ., 2017; Zheng & Ding, 2018; Zheng et al ., 2018). …”

“…The electrophoretic mobility shift assay (EMSA) was performed as described previously (Su et al ., 2017). Briefly, 1–2 μg of purified protein in binding buffer (10 mM Tris‐HCl, pH 7.5, 100 μM KCl, 1 mM EDTA, 100 μg ml −1 bovine serum albumin (BSA), 100 μM ZnCl 2 , 6% glycerol, 1 mM dithiothreitol (DTT)) was mixed with 4 pmol γ‐ 32 P ATP‐labeled probe with or without various dosages of unlabeled probe at 4°C for 1 h. After separation in a 4.5% native non‐denaturing acrylamide gel, the gel was exposed to X‐ray film overnight.…”

“…ChIP assay was performed as described previously (Lu et al ., 2017; Su et al ., 2017). Briefly, 3 g of 80‐d‐old plants was ground and fixed with 1% formaldehyde for 10 min and quenched in 0.125 M glycine.…”

Phytochromes and Phytochrome Interacting Factors

“…A companion study shows that PPKs also phosphorylate CRY2 in response to blue light . In addition, PPKs/MLKs function as a kinase for histone and are involved in the epigenetic regulation of gene expression Su et al, 2017). Phosphorylation of Ser-95 of H2A is necessary for the regulation of FT expression and flowering time under long days.…”

Know Your Histone (Zip) Code: Flowering Time and Phosphorylation of Histone H2A on Serine 95

“…Research aimed at elucidating the temporal connection between all the players involved promises to come to bloom in the near future. ; originally published online September 19, 2017;2017;29;2084-2085 …”