An endoplasmic reticulum-localized NtHSP70-8 confers drought tolerance in tobacco by regulating water loss and antioxidant capacity

Abstract

The 70-kDa heat shock protein (HSP70) is an abiotic stress response factor in plants. However, the functions and underlying molecular mechanisms employed by HSP70 in tobacco have not been studied thoroughly. In this study, we cloned and identified a novel tobacco (Nicotiana tabacum) HSP70 gene, NtHSP70-8, which was upregulated in response to drought stress and treatment with exogenous abscisic acid (ABA) and auxin (IAA). NtHSP70-8 was exclusively localized in the endoplasmic reticulum. NtHSP70-8 overexpression substantially elevated the expression level of NtNCED3, NtNCED 5 (ABA-synthesis gene) and increased the ABA concentration, which caused stomatal closing to prevent water loss under drought conditions. Moreover, NtHSP70-8 overexpression caused a significant reduction in the expression levels of auxin efflux carriers, such as NtPIN1a, NtPIN1c, NtPIN3, NtPIN5, and NtPIN7, and an increase in the IAA concentration, which lowered the stomata density to prevent water loss. Under drought conditions, the NtHSP70-8-overexpressing plants had a substantially higher antioxidant capacity than wild-type tobacco plants, possibly caused by the increased expression of NtSOD, NtPOD, and NtCAT. In contrast, nthsp70-8 tobacco significantly reduced the antioxidant capacity compared with wild-type. Thus, our findings suggest that NtHSP70-8 is an endoplasmic reticulum-localized protein that confers drought tolerance in tobacco by regulating water loss and antioxidant capacity. Furthermore, we demonstrate the involvement of NtHSP70-8 in the interaction between ABA signaling and auxin signaling under drought stress.