Abstract
Increasing the drought tolerance of crops is one of the most challenging goals in plant breeding. To improve crop productivity during periods of water deficit, it is essential to understand the complex regulatory pathways that adapt plant metabolism to environmental conditions. Among various plant hormones and second messengers, calcium ions are known to be involved in drought stress perception and signaling. Plants have developed specific calcium-dependent protein kinases that convert calcium signals into phosphorylation events. In this study we attempted to elucidate the role of a calcium-dependent protein kinase in the drought stress response of barley (Hordeum vulgare L.), one of the most economically important crops worldwide. The ongoing barley genome project has provided useful information about genes potentially involved in the drought stress response, but information on the role of calcium-dependent kinases is still limited. We found that the gene encoding the calcium-dependent protein kinase HvCPK2a was significantly upregulated in response to drought. To better understand the role of HvCPK2a in drought stress signaling, we generated transgenic Arabidopsis plants that overexpressed the corresponding coding sequence. Overexpressing lines displayed drought sensitivity, reduced nitrogen balance index (NBI), an increase in total chlorophyll content and decreased relative water content. In addition, in vitro kinase assay experiments combined with mass spectrometry allowed HvCPK2a autophosphorylation sites to be identified. Our results suggest that HvCPK2a is a dual-specificity calcium-dependent protein kinase that functions as a negative regulator of the drought stress response in barley.
Highlights
Drought stress is one of the most critical threats to world agriculture
Plants have evolved a multigene family of Calcium-dependent protein kinases (CPKs), which are involved in development, stress responses and plant hormone signaling (Ludwig et al, 2004; Yoon et al, 2006; Kobayashi et al, 2007; Ma and Wu, 2007; Myers et al, 2009; Mehlmer et al, 2010; Xu et al, 2010; Asano et al, 2011, 2012; Boudsocq and Sheen, 2013)
We explored the possible role of HvCPK2a in the drought stress response
Summary
Drought stress is one of the most critical threats to world agriculture. The severity and duration of drought are largely unpredictable, but even short periods of water deficit reduce plant growth and crop productivity. Abscisic acid (ABA) is recognized as the most critical hormone in plant responses to water deficit. Many functionally diverse second messengers are involved in drought stress tolerance (Zeng et al, 2015), including calcium and calcium sensors, which are important for signaling and subsequent adaptation to stress conditions (Klimecka and Muszynska, 2007; Kudla et al, 2010; Reddy et al, 2011; Vivek et al, 2013). Calcium-binding proteins play a crucial role in numerous other physiological processes, including hormone signaling and pathogen responses (Sheen, 1996; Romeis et al, 2001; Guo et al, 2002; Fan et al, 2004; Ludwig et al, 2004; Boudsocq and Sheen, 2013)
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