Otomaru, D. | bioRxiv Science

bioRxiv2025

Arabidopsis root-type ferredoxin:NADP(H) oxidoreductases are crucial for root growth and ferredoxin-dependent processes

Root-type ferredoxin:NADP(H) oxidoreductase (RFNR) is believed to reduce ferredoxin using NADPH in nonphotosynthetic tissues, facilitating ferredoxin-dependent biological processes. However, the physiological functions of RFNR remain unclear due to the difficulty in obtaining mutants lacking redundant RFNR isoproteins. The present study successfully generated Arabidopsis homozygous rnfr1;2 double mutants by traditional crossing and selection. However, they displayed severely stunted roots, challenging subsequent growth and abundant seed recovery. Notably, grafted plants combining mutant scions with wild-type rootstocks exhibited normal growth and produced abundant mutant seeds. Growth analysis employing reciprocal grafts with the wild-type and mutant plants showed that primary root growth was inhibited only when the rootstock was derived from the mutants. Meanwhile, the absence of RFNR1 and 2 in the scion had no apparent impact on shoot and root growth. Root transcriptome analysis revealed that RFNR1 and 2 deficiency upregulated genes encoding ferredoxin-dependent enzymes and root-type ferredoxin, leading to genome-wide reprogramming associated with cell walls, lipids, photosynthesis, secondary metabolism, and biotic/abiotic stress responses. Thus, Arabidopsis RFNR1 and 2 are crucial for root growth and various ferredoxin-dependent biological processes.

plant biology↗

bioRxiv2024

Alternative oxidase alleviates mitochondrial oxidative stress during limited nitrate reduction in Arabidopsis thaliana

The conversion of nitrate to ammonium, i.e., nitrate reduction, is a major consumer of reductants in plants. Previous studies have reported that the mitochondrial alternative oxidase (AOX) is upregulated under limited nitrate reduction conditions, including no/low nitrate or when ammonium is the sole nitrogen (N) source. Electron transfer from ubiquinone to AOX bypasses the proton-pumping complexes III and IV, thereby consuming reductants efficiently. Thus, upregulated AOX under limited nitrate reduction may dissipate excessive reductants and thereby attenuate oxidative stress. Nevertheless, so far there is no firm evidence for this hypothesis due to the lack of experimental systems to analyze the direct relationship between nitrate reduction and AOX. We therefore developed a novel culturing system for A. thaliana that manipulates activities of nitrate reduction and AOX separately without causing N starvation, ammonium toxicity, and lack of nitrate signal. Using this system we examined genome-wide gene expression and plant growth to better understand the relationship between AOX and nitrate reduction. Here we show that AOX alleviates mitochondrial oxidative stress and sustains plant growth under limited nitrate reduction.

plant biology↗