ABA3

ABA3 is a gene in Arabidopsis thaliana that encodes a molybdenum cofactor sulfurase. This enzyme is required for the full activity of cytosolic molybdenum cofactor–dependent enzymes, particularly the aldehyde oxidases AO1 and AO3, by supplying sulfur to the molybdenum cofactor. The proper functioning of these enzymes is important for the final step of abscisic acid (ABA) biosynthesis.

Aldehyde oxidases catalyze the conversion of abscisic aldehyde to abscisic acid, the plant hormone that regulates responses to drought, seed dormancy, and other stresses. In plants with loss-of-function mutations in ABA3, AO1 and AO3 activities are compromised, leading to reduced ABA accumulation. This ABA deficiency affects physiological processes such as stomatal closure, water retention, seed germination, and dormancy, and typically results in altered responses to abiotic stresses like drought and salinity.

ABA3 is part of the molybdenum cofactor sulfurase family, enzymes that activate MoCo-dependent oxidoreductases by transferring sulfur to the molybdenum cofactor. In Arabidopsis, ABA3 is commonly described as containing domains associated with MoeB-like activity and sulfur transfer, a configuration shared with plant and bacterial MoCo sulfurases. Orthologs and similar enzymes are found across other plant species, suggesting a conserved role in enabling MoCo enzymes to participate in ABA biosynthesis and related metabolic pathways.

Overall, ABA3 plays a crucial role in enabling the production of ABA by activating aldehyde oxidases, linking MoCo sulfuration to plant hormonal control and stress physiology.