Submitted to: Physiology and Molecular Biology of Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 21, 2007
Publication Date: February 1, 2008
Citation: Shukla, V., Mattoo, A.K. 2008. Sucrose non-fermenting 1-related protein kinase 2 (snrk2): a family of protein kinases involved in hyperosmotic stress signaling. Physiology and Molecular Biology of Plants. 14:91-100.
Interpretive Summary: Crop productivity and quality are compromised when plants face environmental extremes, which include drought, salinity, extreme temperatures and poor soil nutrition. Therefore, there is interest in research to define the responses of plants to such abiotic stresses in order to develop strategies to develop plants with in-built defenses to combat such situations. One common feature of these abiotic stresses is to generate osmotic imbalance and this affect plant performance. It is now realized that plants have developed intricate mechanisms in response to osmotic stress, one of which involves covalent binding and removal of phosphate ions to specific enzymes called protein kinases. One such protein family in plants is called SnRK2 for sucrose non-fermenting protein kinase. In this invited review, we summarize the characteristics – activity, substrates, interacting proteins and gene regulation - of this gene/protein family. Further, we show that several members (nine out of thirteen) of bZIP transcription factors share the same recognition signature, RQXS/T, which suggests that SnRK2 kinases play a major role in plant responses to osmotic stress. This information is of use to scientists interested in developing crops resistant to osmotic stresses.
Our understanding of plant adaptation to abiotic stresses, which include drought, salinity, non-optimal temperatures and poor soil nutrition, is still limiting although significant strides have been made in identifying some of the gene players and signaling partners. Several protein kinases get activated in plants in response to osmotic stress and the stress hormone abscisic acid (ABA). Among these is a superfamily of sucrose non-fermenting protein kinase genes (SnRK2). This review focuses on the developments related to the activity, substrates, interacting proteins and gene regulation of SnRK2 gene family members. Reversible phosphorylation as a crucial regulatory mechanism turns out to be a rule rather than an exception in plant responses to abiotic stress. Nine out of thirteen bZIP transcription factors (ABI5/ABF/AREB family) share the recognition motif, R-Q-X-S/T, suggesting that likely SnRK2 kinases have a major role in regulating gene expression during hyperosmotic stress.