Phosphoproteomic identification of targets of the Arabidopsis sucrose nonfermenting-like kinase SnRK2.8 reveals a connection to metabolic processes

doi:10.1073/pnas.0610208104

Phosphoproteomic identification of targets of the Arabidopsis sucrose nonfermenting-like kinase SnRK2.8 reveals a connection to metabolic processes

Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO 63132

Edited by Clarence A. Ryan, Jr., Washington State University, Pullman, WA, and approved February 6, 2007 (received for review November 16, 2006)

Abstract

SnRK2.8 is a member of the sucrose nonfermenting-related kinase family that is down-regulated when plants are deprived of nutrients and growth is reduced. When this kinase is over expressed in Arabidopsis, the plants grow larger. To understand how this kinase modulates growth, we identified some of the proteins that are phosphorylated by this kinase. A new phosphoproteomic method was used in which total protein from plants overexpressing the kinase was compared with total protein from plants in which the kinase was inactivated. Protein profiles were compared on two-dimensional gels following staining by a dye that recognizes phosphorylated amino acids. Candidate target proteins were confirmed with in vitro phosphorylation assays, using the kinase and target proteins that were purified from Escherichia coli. Seven target proteins were confirmed as being phosphorylated by SnRK2.8. Certain targets, such as 14-3-3 proteins, regulate as yet unidentified proteins, whereas other targets, such as glyoxalase I and ribose 5-phosphate isomerase, detoxify byproducts from glycolysis and catalyze one of the final steps in carbon fixation, respectively. Also, adenosine kinase and 60S ribosomal protein were confirmed as targets of SnRK2.8. Using mass spectrometry, we identified phosphorylated residues in the SnRK2.8, the 14-3-3κ, and the 14-3-3χ. These data show that the expression of SnRK2.8 is correlated with plant growth, which may in part be due to the phosphorylation of enzymes involved in metabolic processes.

Footnotes

^‡To whom correspondence should be addressed. E-mail: dschachtman{at}danforthcenter.org
Author contributions: R.S., J.M.J., and D.P.S. designed research; R.S., S.A., A.Y.B., and D.P.S. performed research; R.S., A.Y.B., J.M.J., and D.P.S. analyzed data; and R.S., J.M.J., and D.P.S. wrote the paper.
↵*Present address: University of Florida, Gainesville, FL 32611.
↵ ^†Present address: University of California, Berkeley, CA 94720.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0610208104/DC1.
Abbreviations:

ADK,

adenosine kinase;

AMPK,

AMP-activated protein kinase;

glyI,

glyoxalase I;

NR,

nitrate reductase;

R5PI,

ribose 5-phosphate isomerase;

RPP2A,

60S ribosomal proteins;

SNF,

sucrose nonfermenting;

SnRK,

SNF1-related protein kinase.