Overexpression of PbrGA2ox1 enhances pear drought tolerance through regulation of GA3-inhibited reactive oxygen species detoxification and abscisic acid signaling1

Abstract

Drought stress represents a devastating natural disaster driven by the continuing intensification of global warming, which seriously threats the productivity and quality of several horticultural crops, including pear. Gibberellins (GAs) play crucial roles in plant growth, development, and responses to drought stress. Previous studies have shown significant reductions of GA levels in plants under drought stress; however, understanding of the intrinsic regulation mechanisms of GA-mediated drought stress in pear remains very limited. Here, we show that drought stress could impair the accumulation of bioactive GAs (BGAs), and subsequently identified PbrGA2ox1 as a chloroplast-localized GA deactivation gene, which was significantly induced by drought stress and abscisic acid (ABA) treatment, but was suppressed by GA3 treatment. PbrGA2ox1-overexpressing transgenic tobacco (Nicotiana benthamiana) plants exhibited enhanced tolerance to dehydration and drought stresses, whereas knock-down of PbrGA2ox1 in pear (Pyrus betulaefolia) by virus-induced gene silencing lead to elevated drought sensitivity. Transgenic plants were hypersensitive to ABA, and had a lower BGAs content, enhanced reactive oxygen species (ROS) scavenging ability, and augmented ABA accumulation and signaling under drought stress compared to wild-type plants. However, the opposite effects were observed with PbrGA2ox1 silencing in pear. Moreover, exogenous GA3 treatment aggravated the ROS toxification effect and restrained ABA synthesis and signaling, resulting in the compromised drought tolerance of pear. In summary, our results shed light on the mechanism by which BGAs are eliminated in pear leaves under drought stress, providing a further insight into the mechanism regulating the effects of the GA on the drought tolerance of plants.