Transcriptome analysis of the shoots of Arabidopsis wild-type and mutants deficient in either or both activities of nitrate reductase and alternative oxidase
The conversion of nitrate to ammonium, known as nitrate reduction, consumes large amounts of reductants in plants. Previous studies have observed that mitochondrial alternative oxidase (AOX) is upregulated under conditions of limited nitrate reduction, such as low or no nitrate availability, or when ammonium serves as the sole nitrogen (N) source. Electron transfer from ubiquinone to AOX bypasses the proton-pumping complexes III and IV, thereby consuming reductants efficiently. Therefore, the upregulation of AOX under conditions of limited nitrate reduction may help dissipate excessive reductants and mitigate oxidative stress. However, firm evidence supporting this hypothesis is lacking due to the absence of experimental systems capable of directly analyzing the relationship between nitrate reduction and AOX. To address this gap, we developed a novel culturing system that allows for the manipulation of nitrate reduction and AOX activities separately, without inducing N starvation, ammonium toxicity, or disrupting the nitrate signal. Using this system, we investigated genome-wide gene expression with RNA-seq to gain insight into the relationship between AOX and nitrate reduction.