Abstract
Calcium-dependent protein kinases (CDPKs) are important sensors of Ca2+ elevations in plant cells regulating the gene expression linked with various cellular processes like stress response, growth and development, metabolism, and cytoskeleton dynamics. Ginger is an extensively used spice due to its unique flavor and immense medicinal value. The two major threats that interfere with the large scale production of ginger are the salinity and drought stress. ZoCDPK1 (Zingiber officinale Calcium-dependent protein kinase 1) is a salinity and drought-inducible CDPK gene isolated from ginger and undergoes dynamic subcellular localization during stress conditions. ZoCDPK1, with signature features of a typical Ca2+ regulated kinase, also possesses a bipartite nuclear localization sequence (NLS) in its junction domain (JD). A striking feature in ZoCDPK1 is the rare occurrence of a coupling between the NLS in JD and consensus sequences in regulatory domain. Here, we further identified its nature of nuclear localization and its interaction partners. In the homology model generated for ZoCDPK1, the regulatory domain mimics the crystal structure of the regulatory domain in Arabidopsis CDPK1. Molecular docking simulation of importin (ZoIMPα), an important protein involved in nuclear translocation, into the NLS of ZoCDPK1 was well-visualized. Furthermore, the direct interaction of ZoCDPK1 and ZoIMPα proteins was studied by the yeast 2-hybrid (Y2H) system, which confirmed that junction domain (JD) is an important interaction module required for ZoCDPK1 and ZoIMPα binding. The probable interacting partners of ZoCDPK1 were also identified using Y2H experiment. Of the 10 different stress-related interacting partners identified for ZoCDPK1, NAC transcription factor (TF) needs special mention, especially in the context of ZoCDPK1 function. The interaction between ZoCDPK1 and NAC TF, in fact, corroborate with the results of gene expression and over-expression studies of ZoCDPK1. Hence ZoCDPK1 is operating through NAC TF mediated ABA-independent, cold non-responsive stress signaling pathway in ginger.
Highlights
Salinity, drought, extreme temperatures, chemical toxicity, pathogen infection, and oxidative stress are serious threats to agriculture and the natural status of the environment (Easterling et al, 2007; Fischer and Edmeades, 2010; Vivek et al, 2013)
Salinity and drought stress are serious impediments in the commercial cultivation of ginger (Vivek et al, 2013; Ajav and Ogunlade, 2014).We have reported earlier that ZoCDPK1, a stress-inducible calcium-dependent protein kinases (CDPKs) in ginger, functions in the positive regulation of the signaling pathways that are involved in the response to salinity and drought stress
To know further about the proteins involved in this signal transduction, we have studied the interaction of ZoCDPK1 with ginger cDNA library
Summary
Drought, extreme temperatures, chemical toxicity, pathogen infection, and oxidative stress are serious threats to agriculture and the natural status of the environment (Easterling et al, 2007; Fischer and Edmeades, 2010; Vivek et al, 2013). Responses to different stress stimuli could be achieved through an increase in intracellular Ca2+ concentrations and relay of divergent Ca2+ signal transduction cascades (Kudla et al, 2010). Specific Ca2+ signatures may be recognized by different sensor proteins. Three major families of Ca2+ sensors have been identified in higher plants: Calmodulins (CaMs) and CaMlike proteins (Perochon et al, 2011), calcineurin B-like (CBL) proteins (Luan, 2009), and calcium-dependent protein kinases (CDPKs) (Deinlein et al, 2014). CDPKs are composed of a Ca2+ sensing and a protein kinase effector domain in a single protein and represent a key player for both perception and signal propagation of intracellular Ca2+ changes upon various stimuli (Deinlein et al, 2014)
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