SOS2-LIKE PROTEIN KINASE5, an SNF1-RELATED PROTEIN KINASE3-Type Protein Kinase, Is Important for Abscisic Acid Responses in Arabidopsis through Phosphorylation of ABSCISIC ACID-INSENSITIVE5.

Xiaona Zhou,Hongmei Hao,Yili Bai,Yuguo Zhang,Yan Guo,Wenbo Zhu,Hong Xu,Huixian Zhao,Yongqing Yang,Feifei Yuan,Karen S Schumaker,Aiguang Guo,Cuiling Cao,Yang Zhao,Chang Gen Xie,Jingjiang Hu,Feiyi Zhao,Yunxia Qin,Mengyao Wang

doi:10.1104/pp.114.255455

Abstract

Abscisic acid (ABA) plays an essential role in seed germination. In this study, we demonstrate that one SNF1-related protein kinase3-type protein kinase, SOS2-like protein kinase5 (PKS5), is involved in ABA signal transduction via the phosphorylation of an interacting protein, abscisic acid-insensitive5 (ABI5). We found that pks5-3 and pks5-4, two previously identified PKS5 superactive kinase mutants with point mutations in the PKS5 FISL/NAF (a conserved peptide that is necessary for interaction with SOS3 or SOS3-like calcium binding proteins) motif and the kinase domain, respectively, are hypersensitive to ABA during seed germination. PKS5 was found to interact with ABI5 in yeast (Saccharomyces cerevisiae), and this interaction was further confirmed in planta using bimolecular fluorescence complementation. Genetic studies revealed that ABI5 is epistatic to PKS5. PKS5 phosphorylates a serine (Ser) residue at position 42 in ABI5 and regulates ABA-responsive gene expression. This phosphorylation was induced by ABA in vivo and transactivated ABI5. Expression of ABI5, in which Ser-42 was mutated to alanine, could not fully rescue the ABA-insensitive phenotypes of the abi5-8 and pks5-4abi5-8 mutants. In contrast, mutating Ser-42 to aspartate rescued the ABA insensitivity of these mutants. These data demonstrate that PKS5-mediated phosphorylation of ABI5 at Ser-42 is critical for the ABA regulation of seed germination and gene expression in Arabidopsis (Arabidopsis thaliana).

Highlights

Abscisic acid (ABA) plays an essential role in seed germination
When bound to ABA, PYRABACIN RESISTANCE1/PYRABACIN RESISTANCE1-LIKE/REGULATORY COMPONENTS OF ABSCISIC ACID RECEPTOR-type ABA receptors interact with and inhibit clade A PROTEIN PHOSPHATASE2C (PP2C). This leads to the release of SNF1-RELATED PROTEIN KINASE2 (SnRK2)-type protein kinases from PP2C-SnRK2 complexes, allowing SnRK2s to phosphorylate and activate downstream effectors of ABA responses, such as ABSCISIC ACID-INSENSITIVE5 (ABI5) and other ABSCISIC ACID-RESPONSIVE ELEMENTBINDING FACTORs (ABFs; Fujita et al, 2009; Cutler et al, 2010)
We found that two hyperactive kinase mutants of PROTEIN KINASE5 (PKS5) (Yang et al, 2010), pks5-3 (Ser-317 replaced by Leu) and pks5-4 (Ala-168 replaced by Val), with amino acid changes in either the FISL/NAF motif or in the kinase activation loop (Guo et al, 2001), were hypersensitive to ABA (Fig. 2, A and B)

Summary

Introduction

Abscisic acid (ABA) plays an essential role in seed germination. In this study, we demonstrate that one SNF1-RELATED PROTEIN KINASE3-type protein kinase, SOS2-LIKE PROTEIN KINASE5 (PKS5), is involved in ABA signal transduction via the phosphorylation of an interacting protein, ABSCISIC ACID-INSENSITIVE5 (ABI5). We found that pks5-3 and pks5-4, two previously identified superactive PKS5 kinase mutants (Yang et al, 2010), are involved in ABA responses during seed germination, root elongation, and gene expression.

Results

Conclusion