The medicinal sage plant (Salvia spp.), belonging to Lamiaceae family, is one of the most important medicinal and aromatic plants. The members of this genus are globally known due to its antimicrobial, antioxidant, astringent, spasmolytic, antihidrotic and specific sensorial properties. In this study, we investigated the potential impact of water deficit on transcript abundance, and essential oil composition of five major metabolites, i.e. 1-8 cineole, a-b-thujone, camphor, and borneol in three genotypes of Salvia spp. Results showed that relative expression of three genes and their corresponding metabolites increased together at three stages under drought condition, but the CS gene transcript decreased independently from 1,8-cineole in garden sage. Furthermore, borneol changed differently compared to the BS gene expression in control and drought treatment plants of S. reuterana (Yasuj). The competitive synthesis of ß-thujone, and a-thujone by SS gene were demonstrated in S. officinalis and Yasuj ecotype of S. reuterana; whereas, no change was observed for Urmia ecotype of S. reuterana. There was no precursor shortage to synthesis of borneol and camphor in garden sage; however increasing the BS led to high production of borneol and low camphor in S. reuterana under drought stress. As a mechanism, secondary metabolites enable the plants to cope with unfavorable conditions, but genetic differences might affect the quantity and quality of these compounds.

Expansins are cell wall proteins that, due to changes in pH, causing the expansion of the cell walls. In this study, a previously gene construct designed based on a root-speci c gene, AtEXPA18, was utilized to assess its potential roles on different morphological, physiological, and cellular levels of generated transgenic tobacco plants in response to moderate and severe drought stress. AtEXPA18 gene was successfully transferred to the tobacco plants through an agrobacterium-mediate transformation system. Upon obtaining the second generation, tobacco transgenic plants were con rmed by conventional polymerase chain reaction (PCR) technique alongside reverse transcription PCR (RT-PCR) using speci c primers. Under drought stress, the transgenic lines showed remarkable growth and signi cantly improved based on morphological traits such as height and stem diameter, leaf area, leaf number, root dry weight, and Abscisic acid (ABA) levels of leaves compared control plants. As a result, the Cytokinin content of transgenic plants has increased under severe stress levels. Notably, the area's expansion for abaxial epidermal cells under the microscope con rmed in transgene cells compared with the -transgene cells. These results, altogether, could support the AtEXPA18 gene implication in cell expansion and improving tolerance capacity of transgenic crops under drought stress.

Expansins are cell wall proteins that, due to changes in pH, causing the expansion of the cell walls. In this study, a previously gene construct designed based on a root-specific gene, AtEXPA18, was utilized to assess its potential roles on different morphological, physiological, and cellular levels of generated transgenic tobacco plants in response to moderate and severe drought stress. AtEXPA18 gene was successfully transferred to the tobacco plants through an agrobacterium-mediate transformation system. Upon obtaining the second generation, tobacco transgenic plants were confirmed by conventional polymerase chain reaction (PCR) technique alongside reverse transcription PCR (RT-PCR) using specific primers. Under drought stress, the transgenic lines showed remarkable growth and significantly improved based on morphological traits such as height and stem diameter, leaf area, leaf number, root dry weight, and Abscisic acid (ABA) levels of leaves compared control plants. As a result, the Cytokinin content of transgenic plants has increased under severe stress levels. Notably, the area's expansion for abaxial epidermal cells under the microscope confirmed in transgene cells compared with the -transgene cells. These results, altogether, could support the AtEXPA18 gene implication in cell expansion and improving tolerance capacity of transgenic crops under drought stress.

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