High impact information on ABA3

• Expression of RD29A-LUC (the firefly luciferase reporter gene under the control of the stress-responsive RD29A promoter) in response to cold and salt/drought is reduced in the los5 mutants, but the response to abscisic acid (ABA) remains unaltered [1].
• A comparison with another ABA-deficient mutant, aba1, reveals that the impaired low-temperature gene regulation is specific to the los5 mutation [1].
• The LOS5/ABA3 gene is expressed ubiquitously in different plant parts, and the expression level increases in response to drought, salt, or ABA treatment [1].
• Our results show that LOS5/ABA3 is a key regulator of ABA biosynthesis, stress-responsive gene expression, and stress tolerance [1].
• However, the sulfur transferase activity of ABA3 is used for post-translational activation of molybdenum enzymes rather than for iron-sulfur cluster assembly [2].

Biological context of ABA3

• The protein binds a pyridoxal phosphate cofactor and a substrate-derived persulfide intermediate, and site-directed mutagenesis of strictly conserved binding sites for the cofactor and the persulfide demonstrated that they are essential for molybdenum cofactor sulfurase activity [2].
• The ABA-deficiency was caused by two monogenic, recessive mutations, aba2 and aba3, that were both located on chromosome 1 [3].
• An expressed sequence tag candidate from tomato was selected on the basis of homology to sulfurases from animals, fungi and the recently isolated Arabidopsis genes LOS5/ABA3 [4].
• Though exploitation of the difference in Car constitution and exciting the WT at 475 and 490 nm, and the ABA-3 mutant at 490 and 515 nm, the different Car contributions to energy transfer have been probed [5].

Associations of ABA3 with chemical compounds

• Although l-selenocysteine is unlikely to be a natural substrate for ABA3, it is decomposed more efficiently than l-cysteine [2].
• ABA3 is a two-domain protein with an NH2-terminal domain sharing significant similarities to NifS proteins that catalyze the decomposition of l-cysteine to l-alanine and elemental sulfur for iron-sulfur cluster synthesis [2].
• This indicates that the aba2 mutant is blocked in the conversion of xanthoxin to ABA-aldehyde and that aba3 is impaired in the conversion of ABA-aldehyde to ABA [6].
• The ABA-3 mutant contains 1.4 Ls and 0.6 zeaxanthin (Z) per monomer [5].
• Co-incubation of partially active aldehyde oxidase and xanthine dehydrogenase with ABA3 C terminus carrying sulfurated molybdenum cofactor resulted in stimulation of aldehyde oxidase and xanthine dehydrogenase activity [7].

Other interactions of ABA3

• In vitro, the NifS-like domain of ABA3 activates aldehyde oxidase and xanthine dehydrogenase in the absence of the C-terminal domain, but in vivo, the C-terminal domain is required for proper activation of both target enzymes [2].

Analytical, diagnostic and therapeutic context of ABA3

• Measurements of ABA revealed that frs1 mutants were ABA deficient, and complementation tests indicated that frs1 mutation was a new allele of the ABA3 locus showing that a mutation in this locus leads to an impairment of freezing tolerance [8].

References