Mitochondrial/Nuclear Regulation of Respiration in Arabidopsis

Michigan State University, East Lansing MI

Investigators

Abstract

Mitochondria have their own genomes, however, the majority of their proteins are nuclear-encoded and the expression and import of these proteins requires a highly regulated, two-way communication between organelles and the nucleus. To date, it has not been feasible to isolate the elements of mitochondrion-nucleus communication in plants. The missing component has been an easily scorable trait for mitochondrial function, one responsive to environmental signals. Plant mitochondria have a branched respiratory pathway with an alternative oxidase (AOX) not coupled to proton translocation and ATP synthesis. Cold, wounding, Reactive Oxygen Species (ROS), and pathogen attack, among others, increase alternative oxidase activity and Aox gene expression. AOX, in the laboratory, is also a dispensable activity in plants, thus its levels may be genetically modified and potential mutants lacking AOX activity recovered. Our research is centered around the isolation of mutants in mitochondrion-nucleus signaling using AOX expression to score for mitochondrial function. We have devised a visual screen for impaired AOX induction after challenge by oxidative stress. To complement this screen, we use microarray analysis to further characterize the mutants, and to identify genes and gene clusters involved in stress-induced AOX expression. Preliminary microarray experiments on mitochondrial gene expression in Arabidopsis leaves establish that this approach can be successful. [Initial data are available online: http://genome www4.stanford.edu/MicroArray/SMD under experimenter "McIntosh"] To ensure complete coverage of the genome we will use oligoarrays, cDNA arrays and directed "mitochondrial" arrays. Mutants in conjunction with transgenic plants will be used to decipher mitochondrial involvement in oxidative stress signaling and cell death, and the role of AOX in the hypevirulence response. AOX and ROS involvement in cell death will be studied through cytochrome c gene family (At-Cc) expression, cytochrome c levels in the mitochondrion and cytosol, and cytochrome pathway activity.