LcMKK , a novel group A mitogen-activated protein kinase kinase gene in Lycium chinense , confers dehydration and drought tolerance in transgenic tobacco via scavenging ROS and modulating expression of stress-responsive genes

The mitogen-activated protein kinase (MAPK) cascades have been previously implicated in signal transduction during plant responses to various environmental stresses. As the convergent point of the MAPK cascades, MAPKKs play paramount roles in amplifying, integrating, and channeling information between the extracellular stimuli and intracellular responses. However, the functional role of MAPKKs in Lycium chinense has never been explored. In this study, a novel MAPKK gene, LcMKK , in L. chinense belonging to group A MAPKKs was isolated and functionally characterized. The transcript level of LcMKK rapidly increased in L. chinense after drought treatments. Overexpression of LcMKK in tobacco conferred dehydration and drought tolerance. Under dehydration and drought conditions, the transgenic tobacco lines exhibited better water status, less accumulation of reactive oxygen species (ROS), higher levels of germination rate and antioxidant enzyme activity than the wild type. In addition, overexpression of LcMKK enhanced the expression of ROS-related and stress-responsive genes under drought conditions. Taken together, these data demonstrate that LcMKK acts as a positive regulator in dehydration/drought stress responses by either regulating ROS homeostasis through the activation of the cellular antioxidant defense system or modulating transcriptional levels of a variety of stress-associated genes.