Overexpression of<i>CaAPX</i>Induces Orchestrated Reactive Oxygen Scavenging and Enhances Cold and Heat Tolerances in Tobacco

Abstract

Ascorbate peroxidase (APX) acts indispensably in synthesizing L-ascorbate (AsA) which is pivotal to plant stress tolerance by detoxifying reactive oxygen species (ROS). Enhanced activity of APX has been shown to be a key step for genetic engineering of improving plant tolerance. However it needs a deeper understanding on the maintenance of cellular ROS homeostasis in response to stress. In this study, we identified and characterized an <i>APX</i> (<i>CaAPX</i>) gene from <i>Camellia azalea</i>. Quantitative real-time PCR (qRT-PCR) analysis showed that <i>CaAPX</i> was expressed in all tissues and peaked in immature green fruits; the expression levels were significantly upregulated upon cold and hot stresses. Transgenic plants displayed marked enhancements of tolerance under both cold and heat treatments, and plant growth was correlated with <i>CaAPX</i> expression levels. Furthermore, we monitored the activities of several ROS-scavenging enzymes including <i>Cu/Zn-SOD</i>, <i>CAT</i>, <i>DHAR</i>, and <i>MDHAR</i>, and we showed that stress tolerance was synchronized with elevated activities of ROS-scavenging. Moreover, gene expression analysis of ROS-scavenging enzymes revealed a role of <i>CaAPX</i> to orchestrate ROS signaling in response to temperature stresses. Overall, this study presents a comprehensive characterization of cellular response related to <i>CaAPX</i> expression and provides insights to breed crops with high temperature tolerances.