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Drought stress severely threatens the yield of cereal crops. Therefore, understanding the molecular mechanism of drought stress response of plants is crucial for developing drought-tolerant cultivars. NAC transcription factors (TFs) play important roles in abiotic stress of plants, but the functions of NAC TFs in sorghum are largely unknown. Here, we characterized a sorghum NAC gene, SbNAC9, and found that SbNAC9 can be highly induced by polyethylene glycol (PEG)-simulated dehydration treatments. We therefore investigated the function of SbNAC9 in drought stress response. Sorghum seedlings overexpressing SbNAC9 showed enhanced drought-stress tolerance with higher chlorophyll content and photochemical efficiency of PSII, stronger root systems, and higher reactive oxygen species (ROS) scavenging capability than wild-type. In contrast, sorghum seedlings with silenced SbNAC9 by virus-induced gene silencing (VIGS) showed weakened drought stress tolerance. Furthermore, SbNAC9 can directly activate a putative peroxidase gene SbC5YQ75 and a putative ABA biosynthesis gene SbNCED3. Silencing SbC5YQ75 and SbNCED3 led to compromised drought tolerance and reduced ABA content of sorghum seedlings, respectively. Therefore, our findings revealed the important role of SbNAC9 in response to drought stress in sorghum and may shed light on genetic improvement of other crop species under drought-stress conditions. [ABSTRACT FROM AUTHOR]

• SbNAC2 can be induced by various abiotic stresses. • Silencing of SbNAC2 leads to compromised drought tolerance of sorghum seedlings. • SbNAC2 can directly induce SbAP37 , a stress-response gene, to enhance the stress tolerance of sorghum. • Heterologous expression of SbNAC2 in Arabidopsis and rice enhanced the stress tolerance of the transgenic plants. Major abiotic stresses such as drought and salinity affect the growth and yield of crops. NAC (NAM, ATAF1/2, and CUC2) is a plant-specific gene family that has been demonstrated to contribute to responses and adaption to abiotic stress in plants. The specific NAC transcription factors (TFs) that play important roles in the response to abiotic stress in sorghum are unknown. Here, we characterized a sorghum TF, SbNAC2, that can be strongly induced by abiotic stresses, including polyethylene glycol (PEG)-simulated dehydration stress treatment, salt treatment, and 4 °C chilling. Knockdown of SbNAC2 in sorghum seedlings by virus-induced gene silencing (VIGS) weakened the drought tolerance of plants. Heterologous overexpression of SbNAC2 in Arabidopsis and rice can induce plant antioxidant enzyme activity under abiotic stress conditions. Furthermore, SbNAC2 directly activates the expression of a stress responsive AP2/ERF type TF gene, SbAP37 , by binding to the TTNCGTA motif of its promoter. These results indicate that SbNAC2 functions as a potentially important regulator in response to abiotic stresses and that it may possibly be used for molecular breeding to enhance crop yields under adverse environmental conditions. [ABSTRACT FROM AUTHOR]