## 2 Results
### TrHSFB2a Negatively Regulates Drought Tolerance in Transgenic Overexpression Arabidopsis
(**f**) Display the morphology of _TrHSFB2a_ overexpression lines, T-DNA lines and Wt type plants in soil, (**g**) relative gene expression in overexpression lines, (**h–j**) display root length (cm), fresh weight (g) and dry weight (g), respectively, of wild and transgenic plants under normal growth condition. Bars represent mean \(\pm\) SD values, and different small letters (a, b and c) represent significant statistical difference among means (one-way ANOVA, followed by Tukey test) between different lines. and dried, while wild-type plants showed less wilting compared to the overexpression lines, while T-DNA lines did not exhibit leaf wilting at this stage (Figure 6a). Three days after rewatering, more than 70% of wild-type plants recovered, while only about 30% of overexpression plants could survive. These observations indicated that the overexpression of _TrHSFB2a_ significantly reduced drought tolerance, while suppressing its expression significantly increased drought tolerance in transgenic _Arabidopsis_ at the seedling stage. Fresh weight, dry weight and photochemical efficiency determine how plants grow under stressed conditions. Relative water contents (RWC) of the plant showed their water status in terms of physiological consequences under water-deficient conditions. The cell membrane permeability and lipid peroxidation are the general indicators of damage in plants caused by different stresses and are measured as REC of electrolyte leakage and malondialdehydeehyde (MDA) contents, respectively. Lipid peroxidation is generally associated with the oxidation of lipids of the cell membrane; thus, its quantification determines the extent of cell membrane damage. In the current study, the phytochemical efficiency of photosystem II and performance index was determined after 10 days of water withholding. Results showed that overexpression lines had significantly reduced photochemical efficiency of Photosystem II and the performance index compared to wild type, while T-DNA lines had significantly higher photochemical efficiency of photosystem II and performance index than that of wild type. Similarly, fresh weight, dry weight and RWC were significantly lower in overexpression lines compared to wild type and were significantly higher in T-DNA lines compared to wild type (Figure 6). In contrast, REC and MDA contents were significantly higher in overexpressed lines than that of wild type and significantly lower in T-DNA lines than that of wild type (Figure 6). These results, along with phenotypic data, demonstrated that _TrHSFB2a_ negatively regulates drought stress, and RNA interference in T-DNA lines improved the drought tolerance in _Arabidopsis_. Figure 5: Comparison of drought-stress responses of overexpressing _TrHSFB2a_ lines and RNA interference T-DNA lines and wild type grown on 1/2 MS medium (with 3% sucrose + 0.7% agar) supplemented with 200 or 300 mM mannitol. **(a,b)** Display overexpression _TrHSFB2a Arabidopsis thaliana_ along with wild type grown on 1/2 MS medium supplemented with 200 and 300 mM mannitol, respectively, **(c,d)** show plant with roots growth on 1/2 MS medium supplemented with 200 and 300 mM mannitol, respectively. **(e)** Root length on 1/2 MS medium supplemented with 200 and 300 mM mannitol, respectively. **(f)** Plant-yellowing rate on 1/2 MS medium supplemented with 200 mM mannitol. Bars represent mean \(\pm\) SD values, and different small letters (a, b, and c) represent significant statistical difference among means (one-way ANOVA, followed by Tukey test) between different lines.