Overexpression of tomato mitogen-activated protein kinase SlMPK3 in tobacco increases tolerance to low temperature stress

Abstract

Mitogen-activated protein kinase (MAPK) cascades are important intracellular signaling events that mediate signal transduction associated with plant responses to environmental stresses. In this study, tomato plants were subjected to treatments of low (4 °C) and high-temperature (42 °C) and exogenous application of methyl jasmonate, salicylic acid and hydrogen peroxide. Results show that tomato leaves from treated plants contained an elevated level of the MAPK gene (SlMPK3). Transient expression assay of onion epidermal cells using pBI121-GFP constructs indicate that the SlMPK3 was predominantly localized in nuclei. In transgenic tobacco plants overexpressing SlMPK3, leaves contained less reactive oxygen species (ROS), more superoxide dismutase, peroxidase, catalase, ascorbate peroxidase activities, higher proline and soluble sugar contents, and an elevated transcript level of stress-responsive genes. Seeds derived from those SlMPK3 transgenic tobacco plants had a significant higher germination rate (P < 0.05) under chilling stress (12 °C). The transgenic seedlings also developed larger root system under the same temperature treatment conditions. Taken together, these data demonstrate that SlMPK3 acts as a positive regulator in the response to low temperature stress by regulating ROS homeostasis through activation of cellular antioxidant systems and modulating the transcription of stress-associated genes.