NIH Postdoctoral Fellow Rice University Rosharon, Texas
Photosynthesis is essential for plant function and, by extension, most life on the planet. However, this high-energy chemistry is also a liability for the chloroplasts and cells in which it takes place. Photosynthesis naturally produces reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide, and hydrogen peroxide. Under environmental stresses (e.g., drought, excess light, extreme temperatures, and pathogen attack), photosynthetically-produced ROS can overwhelm existing safety measures and will oxidize macromolecules such as DNA, lipids, and proteins. This photo-oxidative stress can then lead to photo-inhibition, turn-over of the chloroplast, and eventually cell death. However, ROS-induced cellular degradation is often the result of a genetic signal rather than direct toxicity of the ROS. Such signals may be used to eliminate damaged chloroplasts and cells and/or to redistribute nutrients to sink tissues. Many chloroplast ROS signaling pathways that control chloroplast turn-over and programmed cell death (PCD) exist, but their signaling mechanisms remain obscure. To identify factors involved in such photo-oxidative stress signaling, we have performed a new forward genetic screen to identify mutations that block chloroplast 1O2-induced PCD. This screen was performed in the Arabidopsis thalianaplastid ferrochelatase two (fc2) mutant, which conditionally produces chloroplast 1O2 and signals for chloroplast degradation and PCD. We have mutated fc2 with activation-tagging constructs and screened for dominant gain-of-function suppressors of 1O2-induced PCD and signaling. Here we describe the isolation of nine fc2activation-tagged suppressors (fas) mutants and their initial characterization. One mutation, fas2, has been mapped to a gene encoding an AP2-type transcription factor broadly involved in chloroplast photo-oxidative stress. Together, these findings provide new genetic tools for uncovering chloroplast stress signaling mechanisms used to maintain healthy populations of photosynthesizing chloroplasts under dynamic environments.