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Calcineurin-B-like proteins (CBLs) are essential components of the calcium signaling network and act during plant's response to stress and normal conditions. A combined research strategy of in-silico analysis and gene silencing experiment was employed to investigate the role of different classes of CBLs in tomato (Solanum lycopersicum L.) during the response to drought stress. Two different classes of CBL genes, including SlCBL3-1 , and SlCBL3-2 , with the minimum and a maximum number of drought-responsive cis-elements, were selected and were targeted for transient gene silencing in tomato followed by the drought treatment. The effect of silencing events was evaluated by determining of further growth and physiological traits in plants under both control and drought stress conditions. The results showed that silencing of SlCBL3-1 significantly reduced shoot and root growth, relative water content (RWC), and the concentration of pigments while increased free radical accumulation, lipid peroxidation, and leakage from the cells. On the other hand, no antioxidant enzyme activity or proline induction was triggered in plants after SlCBL3-1 silencing. Some of these adverse events were more significantly enhanced when the silenced plants were exposed to drought stress. Overall, a significant role for SlCBL3-1 in the life cycle of plant suggested under both normal and stress conditions. The SlCBL3-2 silencing showed more efficient plants recovery from silencing or drought stress conditions. Therefore, SlCBL3-2 gene may act as a negative regulator under stress conditions. The results might provide new theoretical insight and genetic resources for developing resistant crops against environmental stresses. • Different classes of Calcineurin B-like (CBL) proteins regulate the plant responses during normal or stress conditions. • SlCBL3-1 plays a critical role in maintaining hemostasis in life cycle of plants under both normal and stress conditions. • SlCBL3-2 that is another class of CBL may act as a negative regulator under stress conditions. • A low copy number of cis-element in the promoter of CBL gene is sufficient to trigger a proper stress-induced response. [ABSTRACT FROM AUTHOR]

The growth and physiological parameters of fourteen tomato cultivars were measured during both mild and severe drought. The tomato cultivars showed decrease in growth traits, relative water content and pigments content under both drought treatments compared with the control. By contrast, proline accumulation, malondialdehyde and electrolyte leakage increased in the cultivars. The activity of superoxide dismutase was more correlated to drought stress than those of ascorbate peroxidase or catalase. The combined approach of principal component analysis, hierarchical clustering analysis and calculating mean tolerance value showed relative differences in drought tolerance among the cultivars. The studied cultivars were clustered into four groups. Four cultivars were placed in cluster I as the drought-tolerant group. Moderately tolerant cultivars were grouped into Cluster II. The clusters III and IV represented the sensitive and highly sensitive cultivars, respectively. Early orbana, Roma and Cal-j cultivars were indicated as the highly sensitive tomato cultivars. It was concluded that such an approach could be used as a useful tool to screen the other abiotic or even biotic stress tolerance in tomato. [ABSTRACT FROM AUTHOR]