Regulation of reactive oxygen species generation under drought conditions in Arabidopsis.

Reactive oxygen species (ROS) are produced when plants are exposed to environmental stresses, such as drought and heat conditions. Oxidative stress imposed by ROS under drought conditions profoundly affects plant growth and development. However, ROS production and scavenging mechanisms under adverse environmental conditions are largely unknown. We have recently reported that a NAM/ATAF1/2/CUC2 (NAC) transcription factor NTL4 is required for generation of ROS under drought conditions in Arabidopsis. 35S:4ΔC transgenic plants overexpressing a truncated NTL4 form (4ΔC) lacking the C‑terminal transmembrane (TM) motif were hypersensitive to drought stress, and ROS accumulated to a high level in the transgenic plants. In contrast, NTL4-deficient ntl4 mutants were less sensitive to drought stress and contained reduced levels of ROS. Furthermore, the plasma membrane-associated NTL4 transcription factor is proteolytically activated by treatments with drought and abscisic acid (ABA) and nuclear-localized, where it induces expression of NADPH oxidase genes involved in ROS biosynthesis. Notably, the 35S:4ΔC transgenic plants showed accelerated leaf senescence and cell death under drought conditions. Taken together, these observations indicate that NTL4 regulation of ROS generation underlies the drought-induced leaf senescence.