Light Primes the Thermally Induced Detoxification of Reactive Oxygen Species During Development of Thermotolerance in Arabidopsis.

Reactive oxygen species (ROS) serve as critical signaling mediators in plant adaptation responses to environmental stimuli. ROS biosynthesis and metabolism should be tightly regulated, because they often impose oxidative damage on biological molecules, such as DNA and proteins, and on cellular structures. It is known that at high temperatures, ROS rapidly accumulate in plant tissues. Thus, a quick activation of ROS-scavenging systems is necessary for thermal adaptation. However, it is largely unknown how the thermo-induced ROS-detoxifying capacity is enhanced by environmental factors at the molecular level. Here, we demonstrated that environmental light primes the thermally induced ROS detoxification process for development of thermotolerance in Arabidopsis. While the ROS detoxification capacity was markedly enhanced in light-pre-treated plants at high temperatures, its enhancement was not as evident in dark-pre-treated plants. ASCORBATE PEROXIDASE 2 (APX2) is a representative ROS-scavenging enzyme that is activated under heat stress conditions. It was observed that the thermal induction of the APX2 gene was more prominent in light-pre-treated plants than in dark-pre-treated plants. Notably, the light-gated APX2 gene induction was compromised in Arabidopsis mutants lacking the red light photoreceptor phytochrome B (phyB). Furthermore, exogenous application of the antioxidant ascorbate recovered the heat-sensitive phenotype of the phyB mutant. These observations indicate that light-primed ROS-detoxifying capability is intimately linked with the induction of thermotolerance. We propose that the phyB-mediated light priming of ROS detoxification is a key component of thermotolerant adaptation in plants.