Casein kinase 2 α and β subunits inversely modulate ABA signal output in Arabidopsis protoplasts
Our transient gene expression analyses in Arabidopsis protoplasts support the view that CK2αs and CK2βs positively and negatively modulate ABRE-dependent gene expression, respectively.
The phytohormone abscisic acid (ABA) regulates the expression of thousands of genes via ABA-responsive elements (ABREs), and has a crucial role in abiotic stress response. Casein kinase II (CK2), a conserved Ser/Thr protein kinase in eukaryotes, is essential for plant viability. Although the CK2 has been known as a tetrameric holoenzyme comprised of two catalytic α and two regulatory β subunits, each of the two types of subunits has been proposed to have independent functions. The Arabidopsis genome encodes four α subunits (CK2α1, CK2α2, CK2α3, CK2α4) and four β subunits (CK2β1, CK2β2, CK2β3, CK2β4). There is a growing body of evidence linking CK2 to ABA signaling and abiotic stress responses. However, the roles of each CK2 subunit in ABA signaling remain largely elusive. Using the transient expression system with the core ABA signaling components in Arabidopsis leaf mesophyll protoplasts, we show here that CK2α1 and CK2α2 (CK2α1/2) positively modulate ABRE-dependent gene expression as ABA signal output in ABA signaling, whereas all four CK2βs negatively modulate the ABRE-dependent gene expression mediated by subclass III SnRK2–AREB/ABF pathway and by CK2α1/2. These data indicate that CK2α1/2 and CK2βs positively and negatively modulate ABA signal output, respectively, suggesting that the quantitative balance of CK2 subunits determines the ABA signal output in plants. Given that CK2s act as pleiotropic enzymes involved in multiple developmental and stress–responsive processes, our findings suggest that CK2 subunits may be involved in integration and coordination of ABA-dependent and -independent signaling.
KeywordsABA-responsive-elements Abscisic acid signaling Arabidopsis thaliana AREB/ABFs Protoplast transient expression system SnRK2
Casein kinase II
Casein kinase II subunits
Group-A protein phosphatase 2C
Pyrabactin resistance1/PYR1-like/regulatory components of ABA receptor
Subclass III sucrose nonfermenting 1 related protein kinase 2
We thank U. Mitsuyasu, T. Yoshida, E. Ohgawara, K. Mogami, M. Kishimoto, N. Takano, R. Motohashi, I. Saito, and M. Ikegami for excellent technical support, M. Toyoshima for skillful editorial assistance, and T. Ogata for critical reading of the manuscript.
This research was supported in part by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan Grants-in-Aid for Scientific Research (C) (nos. 24510312 and 16K07412 to YF) and the Ministry of Agriculture, Forestry and Fisheries (MAFF) of Japan (to YN, YF).
Compliance with ethical standards
Conflict of interest
The authors declare no conflicts of interest.
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