464 / 2019-02-27 08:08:07

A Plant-specific H2A Phosphorylation Modulates Flowering Time and Hypocotyl Elongation

histone phosphorylation, flowering time, plant specific

Epigenetic Regulation > Epigenetic Regulation

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 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 CCA1, which allows MLK4 to bind to the GI promoter. CCA1 interacts with YAF9a, a co-subunit of the SWR1and 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.
MLK1 and MLK2 interact with RGA. Loss of MLK1 and MLK2 function results in plants with short hypocotyls and hyposensitivity to GAs. MLK1/2 and RGA directly interact with CCA1, which targets the promoter of DWF4 to regulate its roles in cell expansion. MLK1/2 antagonize the ability of RGA to bind CCA1, and these factors coordinately regulate the expression of DWF4. RGA suppressed the ability of CCA1 to activate expression from the DWF4 promoter, but
MLK1/2 reversed this suppression. Genetically, MLK1/2 act in the same pathway as RGA and CCA1 in hypocotyl elongation.