Abstract
Climate change, currently taking place worldwide and also in the Mediterranean area, is leading to a reduction in water availability and to groundwater salinization. Olive represents one of the most efficient tree crops to face these scenarios, thanks to its natural ability to tolerate moderate salinity and drought. In the present work, four olive cultivars (Koroneiki, Picual, Royal de Cazorla and Fadak86) were exposed to high salt stress conditions (200 mM of NaCl) in greenhouse, in order to evaluate their tolerance level and to identify key genes involved in salt stress response. Molecular and physiological parameters, as well as plant growth and leaves’ ions Na+ and K+ content were measured. Results of the physiological measurements showed Royal de Cazorla as the most tolerant cultivar, and Fadak86 and Picual as the most susceptible ones. Ten candidate genes were analyzed and their complete genomic, CDS and protein sequences were identified. The expression analysis of their transcripts through reverse transcriptase quantitative PCR (RT-qPCR) demonstrated that only OeNHX7, OeP5CS, OeRD19A and OePetD were upregulated in tolerant cultivars, thus suggesting their key role in the activation of a salt tolerance mechanism.
Highlights
The Mediterranean area is sensitive to climate change [1], that will lead to a reduction in water availability and to groundwater salinization in the near future [2]
Expressed genes related to salt tolerance were identified in olive [52,53], showing that tolerance to high salinity depends on the genotype, as demonstrated by a lot of other evidence [10,11,22,59], and that this trait is associated with the ability of olive trees to retain Na+ and Cl− ions in the roots [9,13,60]
The OeBBX19 analyzed in this study effectively showed over-expression in Royal plants at 210 DATS, confirming the effect of this gene to increase salt tolerance, but its upregulation in the most susceptible and damaged cultivar
Summary
The Mediterranean area is sensitive to climate change [1], that will lead to a reduction in water availability and to groundwater salinization in the near future [2]. Olive tree (Olea europaea L.), considered one of the most important crops of the Mediterranean area, is able to face the environmental changes and develop adaptive mechanisms, thanks to its huge varietal patrimony [3,4,5,6]. Several studies have focused on the response of different olive cultivars to salt stress [7,10,11,12,13], but the mechanisms involved in salt tolerance are still required to be adequately recognized. The adaptive response to salinity stress includes the active exclusion of sodium (Na+ ) ions and/or their sequestration into the vacuole, production of compatible solutes and detoxification of reactive oxygen species (ROS) [15]
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