Calcium-dependent protein kinase 2 is an early player in the salt stress response

Abstract

Potato is the most important horticultural crop in Argentina. It is well adapted to many environmental conditions but certain abiotic stresses, such as salinity, cause significant reductions in growth and yield. Understanding how potato plants perceive and combat salt stress is fundamental to develop salt-tolerant plants that could expand actual crop frontiers. When exposed to NaCl, plants exhibit fast and transient increases in cytosolic Ca2+ within seconds; this early and prominent feature needs to be decoded by calcium sensors that transduce this signal into physiological responses. In greenhouse potato plants irrigated with high salt (50 or 150 mM NaCl), shoot and root length, and shoot biomass showed a significant reduction, and photosynthetic parameters were strongly affected compared to control plants. In this report, we carried out an in silico analysis of the cis-responsive elements found in the promoter sequences of three CDPK isoforms: StCDPK1, StCDPK2, and StCDPK3. Numerous sites related to abiotic stress were predicted in the three promoters; however, these were more abundant in StCDPK2. In accordance with this, GUS activity increased in the root tips of ProStCDPK2:GUS potato plants upon salt stress. RT-qPCR assays confirmed its early induction in in vitro potato plants after 2 h of high salt exposure. Moreover, StCDPK2 expression was induced when greenhouse plants were exposed to a dynamic salt stress condition. Based on these data, we produced 35S:StCDPK2 plants to further analyze the role of this kinase under salt stress conditions. As inferred from biometric data and chlorophyll content, plants that over-express StCDPK2 were more tolerant than WT plants when exposed to high salt in vitro. Over-expressing plants showed enhanced expression of WRKY6 and ERF5 transcription factors under control conditions and reduced accumulation of peroxide and higher catalase activity under salt conditions. Our results show that StCDPK2 is an early player in the salt stress response.