Abstract
Cultivated olive, a typical fruit crop species of the semi-arid regions, could successfully face the new scenarios driven by the climate change through the selection of tolerant varieties to salt and drought stresses. In the present work, multidisciplinary approaches, including physiological, epigenetic and genetic studies, have been applied to clarify the salt tolerance mechanisms in olive. Four varieties (Koroneiki, Royal de Cazorla, Arbequina and Picual) and a related form (O. europaea subsp. cuspidata) were grown in a hydroponic system under different salt concentrations from zero to 200 mM. In order to verify the plant response under salt stress, photosynthesis, gas exchange and relative water content were measured at different time points, whereas chlorophyll and leaf concentration of Na+, K+ and Ca2+ ions, were quantified at 43 and 60 days after treatment, when stress symptoms became prominent. Methylation sensitive amplification polymorphism (MSAP) technique was used to assess the effects of salt stress on plant DNA methylation. Several fragments resulted differentially methylated among genotypes, treatments and time points. Real time quantitative PCR (RT-qPCR) analysis revealed significant expression changes related to plant response to salinity. Four genes (OePIP1.1, OePetD, OePI4Kg4 and OeXyla) were identified, as well as multiple retrotransposon elements usually targeted by methylation under stress conditions.
Highlights
Cultivated olive (Olea europaea subsp. europaea var. europaea) is a long-living, evergreen, thermophilic species
Among the five studied genotypes, the cuspidata samples resulted extremely susceptible to NaCl treatment and all replicates died after 14 days since treatment starting, while the control plants were growing well in hydroponic condition, it was not possible to include them in further experiments (Fig. 1A)
A multidisciplinary approach was applied to shed light on the physiological, genetic and epigenetic changes activated in olive trees in response to salinity stress
Summary
Cultivated olive (Olea europaea subsp. europaea var. europaea) is a long-living, evergreen, thermophilic species. A deeper understanding on how plants respond to different level of salinity stress and the development of integrated combination of genetic, epigenetic and physiological techniques will represent important pre-requisites for the development of salt-tolerant varieties[4]. Recent research has identified various adaptive responses to salinity stress at molecular, metabolic and physiological level, mechanisms underlying salinity tolerance are far from being completely explained. When plants are exposed to stressful conditions, including salinity, the mechanisms of adaptation are activated, allowing the plant to react. In this regard, cytosine methylation may play an integral role in the regulation of gene expression at both, transcriptional and post-transcriptional levels[19,20]. Several studies have demonstrated that cytosine methylation plays an important role in regulating various biotic and abiotic stresses, such as low temperature[21,22,23], water deficiency[24], bacteria blight[25], ion implantation[26], heavy metals[27], low nutrients[28,29], tissue culture[30,31] and salt stress[32]
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