Overexpression of E. coli formaldehyde metabolic genes pleiotropically promotes Arabidopsis thaliana growth by regulating redox homeostasis.

Formaldehyde (FA) is a hazardous pollutant causing acute and chronic poisoning in humans. While plants provide a natural method of removing FA pollution, their ability to absorb and degrade FA is limited. To improve the ability of plants to degrade FA, we introduced the E. coli FrmA gene into Arabidopsis thaliana alone (FrmAOE lines) or with FrmB (FrmA/BOE lines). The transgenic seedlings had approximately 30 % longer primary roots and a 20 % higher fresh weight than the control plants. The transgenic plants started flowering four days earlier and had about 30 % more kilo-seed weight than the wild type. FrmA/BOE and FrmAOE accumulated 40 % more reactive oxidative species (ROS) in mesophyll protoplasts and leaf tissue than wild-type plants under normal conditions. In the presence of FA, they produced 92 % and 26 % more glutathione (GSH) and 6 % and 4 % more ascorbate (AsA), respectively, compared to wild-type plants and thus scavenged FA-induced ROS more effectively. The degradation efficiency of the transgenic leaf extract for FA was 73 % and 44 % higher than that of the wild type, respectively, which was also emphasized by a 2 %-26 % increase in the activity of antioxidant enzymes such as SOD and APx. By revealing the functional divergence between microbial and plant FA metabolic pathways, our work has not only highlighted the promising pluripotency of microbial genes in promoting normal plant growth and detoxifying organic pollutants simultaneously, but also revealed another layer of complexity of plant defense mechanisms against organic toxins related to ROS scavenging.