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Abstract
YUCCA (YUC) proteins constitute a family of flavin monooxygenases (FMOs), with an important role in auxin (IAA) biosynthesis. Here we report that Arabidopsis plants overexpressing YUC6 display enhanced IAA-related phenotypes and exhibit improved drought stress tolerance, low rate of water loss and controlled ROS accumulation under drought and oxidative stresses. Co-overexpression of an IAA-conjugating enzyme reduces IAA levels but drought stress tolerance is unaffected, indicating that the stress-related phenotype is not based on IAA overproduction. YUC6 contains a previously unrecognized FAD- and NADPH-dependent thiol-reductase activity (TR) that overlaps with the FMO domain involved in IAA biosynthesis. Mutation of a conserved cysteine residue (Cys-85) preserves FMO but suppresses TR activity and stress tolerance, whereas mutating the FAD- and NADPH-binding sites, that are common to TR and FMO domains, abolishes all outputs. We provide a paradigm for a single protein playing a dual role, regulating plant development and conveying stress defence responses.
Highlights
YUCCA (YUC) proteins constitute a family of flavin monooxygenases (FMOs), with an important role in auxin (IAA) biosynthesis
To investigate whether the drought tolerance phenotype conferred by YUC6 overexpression could be attributed to high-auxin content, we first performed experiments to corroborate that overexpression of YUC6 increases drought tolerance in Arabidopsis (Supplementary Fig. 1)
Because reduction of YUC6 by NADPH takes place regardless of the presence of substrates, YUC6 may become an NADPH oxidase using the electrons from NADPH to convert oxygen into hydrogen peroxide
Summary
YUCCA (YUC) proteins constitute a family of flavin monooxygenases (FMOs), with an important role in auxin (IAA) biosynthesis. These data indicate that drought tolerance of the yuc6-1D mutant correlated with the ability to limit ROS accumulation in response to drought stress but not with high-auxin content (Fig. 1a–e).
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