BRI1-EMS-SUPPRESSOR 1 (BES1) transcription factor is closely associated with the brassinosteroid (BR) signaling pathway and plays an important role in plant growth and development.  SLB3 is a member of BES1 transcription factor family and its expression was previously shown to increase significantly in tomato seedlings under drought stress.  In the present study,we used virus-induced gene silencing (VIGS) technology to downregulate SLB3 expression to reveal the function of the SLB3 gene under drought stress further.  The downregulated expression of SLB3 weakened the drought tolerance of the plants appeared earlier wilting and higher accumulation of H₂O₂ and O₂^–·, decreased superoxide dismutase (SOD) activity, and increased proline (PRO) and malondialdehyde (MDA) contents and peroxidase (POD) activity.  Quantitative real-time PCR (qRT-PCR) analysis of BR-related genes revealed that the expression of SlCPD, SlDWARF and BIN2-related genes was significantly upregulated in SLB3-silenced seedlings under drought stress, but that the expression of TCH4-related genes was downregulated.  These results showed that silencing the SLB3 gene reduced the drought resistance of tomato plants and had an impact on the BR signaling transduction which may be probably responsible for the variation in drought resistance of the tomato plants. 

Zinc finger-homeodomain proteins (ZF-HDs) are transcription factors that regulate plant growth, development, and abiotic stress tolerance.  The SL-ZH13 gene was found to be significantly upregulated under drought stress treatment in tomato (Solanum lycopersicum) leaves in our previous study.  In this study, to further understand the role that the SL-ZH13 gene plays in the response of tomato plants to drought stress, the virus-induced gene silencing (VIGS) method was applied to downregulate SL-ZH13 expression in tomato plants, and these plants were treated with drought stress to analyze the changes in drought tolerance.  The SL-ZH13 silencing efficiency was confirmed by quantitative real-time PCR (qRT-PCR) analysis.  In SL-ZH13-silenced plants, the stems wilted faster, leaf shrinkage was more severe than in control plants under the same drought stress treatment conditions, anyd the mean stem bending angle of SL-ZH13-silenced plants was smaller than that of control plants.  Physiological analyses showed that the activity of superoxide dismutase (SOD) and peroxidase (POD) and the content of proline (Pro) in SL-ZH13-silenced plants were lower than those in control plants after 1.5 and 3 h of drought stress treatment.  The malondialdehyde (MDA) content in SL-ZH13-silenced plants was higher than that in control plants after 1.5 and 3 h of drought stress treatment, and H₂O₂ and O₂^-· accumulated much more in the leaves of SL-ZH13-silenced plants than in the leaves of control plants.  These results suggested that silencing the SL-ZH13 gene affected the response of tomato plants to drought stress and decreased the drought tolerance of tomato plants.