Yuhan Hao, Haijiao Wang, Shenglong Qiao, Linna Leng, and Xuelu Wang

Significance

The brassinosteroid (BR) signaling pathway has important functions in plant development, but the mechanisms that control its key regulator BR-INSENSITIVE 2 (BIN2) remain poorly understood. We found that the histone deacetylase HDA6 can interact with and deacetylate BIN2 to inhibit its activity, providing significant insights into the repression of BIN2 and the function of the histone deacetylase in modifying nonhistone proteins. We also found that this repression may be related to energy status in plants.

Abstract

Glycogen synthase kinase 3 (GSK3)-like kinases play important roles in brassinosteroid (BR), abscisic acid, and auxin signaling to regulate many aspects of plant development and stress responses. The Arabidopsis thaliana GSK3-like kinase BR-INSENSITIVE 2 (BIN2) acts as a key negative regulator in the BR signaling pathway, but the mechanisms regulating BIN2 function remain unclear. Here we report that the histone deacetylase HDA6 can interact with and deacetylate BIN2 to repress its kinase activity. The hda6 mutant showed a BR-repressed phenotype in the dark and was less sensitive to BR biosynthesis inhibitors. Genetic analysis indicated that HDA6 regulates BR signaling through BIN2. Furthermore, we identified K189 of BIN2 as an acetylated site, which can be deacetylated by HDA6 to influence BIN2 activity. Glucose can affect the acetylation level of BIN2 in plants, indicating a connection to cellular energy status. These findings provide significant insights into the regulation of GSK3-like kinases in plant growth and development.

See: http://www.pnas.org/content/113/37/10418.abstract.html?etoc

PNAS September 13 2016; vol.113; no.37: 10418–10423

Fig. S4.

Proposed model. BIN2, an important negative regulator in the BR signaling pathway, is regulated by upstream BR signals through phosphorylation. Phosphorylated and acetylated BIN2 has higher activity to phosphorylate the downstream transcription factors BES1 and BZR1 to inhibit BR signaling. Under energy-limited conditions, HDA6 interacts with BIN2 and deacetylates BIN2 on the K189 site to inhibit BIN2 activity and promote BR signaling. The expression of HDA6 can be feedback-inhibited, likely through BES1- and BZR1-mediated transcription regulation. HDA6 may also interact with BES1 to regulate its transcription activity.