Suppression of the Gene Affects the Level of ROS Depending on Light and Cold.

The E3 ubiquitin-protein ligase HOS1 is an important integrator of temperature information and developmental processes. HOS1 is a negative regulator of plant cold tolerance, and silencing leads to increased cold tolerance. In the present work, we studied ROS levels in plants, in which the gene was silenced by disruption of the open reading frame via CRISPR/Cas9 technology. Confocal imaging of intracellular reactive oxygen species (ROS) showed that the mutation moderately increased levels of ROS under both low and high light (HL) conditions, but wild-type (WT) and plants exhibited similar ROS levels in the dark. Visualization of single cells did not reveal differences in the intracellular distribution of ROS between WT and plants. The plants contained a high basal level of ascorbic acid, maintained a normal balance between reduced and oxidized glutathione (GSH and GSSG), and generated a strong antioxidant defense response against paraquat under HL conditions. Under cold exposure, the mutation decreased the ROS level and substantially increased the expression of the ascorbate peroxidase genes and . When plants were pre-exposed to cold and further exposed to HL, the expression of the NADPH oxidase genes and was increased in the plants but not in WT plants. -mediated changes in the level of ROS are cold-dependent and cold-independent, which implies different levels of regulation. Our data indicate that is required to maintain ROS homeostasis not only under cold conditions, but also under conditions of both low and high light intensity. It is likely that prevents the overinduction of defense mechanisms to balance growth.