title: Auxin activates the plasma membrane H+-ATPase by phosphorylation during hypocotyl elongation in Arabidopsis.
abstract: The phytohormone auxin is a major regulator of diverse aspects of plant growth and development. The ubiquitin-ligase complex SCF(TIR1/AFB) (for Skp1-Cul1-F-box protein), which includes the TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX (TIR1/AFB) auxin receptor family, has recently been demonstrated to be critical for auxin-mediated transcriptional regulation. Early-phase auxin-induced hypocotyl elongation, on the other hand, has long been explained by the acid-growth theory, for which proton extrusion by the plasma membrane H(+)-ATPase is a functional prerequisite. However, the mechanism by which auxin mediates H(+)-ATPase activation has yet to be elucidated. Here, we present direct evidence for H(+)-ATPase activation in etiolated hypocotyls of Arabidopsis (Arabidopsis thaliana) by auxin through phosphorylation of the penultimate threonine during early-phase hypocotyl elongation. Application of the natural auxin indole-3-acetic acid (IAA) to endogenous auxin-depleted hypocotyl sections induced phosphorylation of the penultimate threonine of the H(+)-ATPase and increased H(+)-ATPase activity without altering the amount of the enzyme. Changes in both the phosphorylation level of H(+)-ATPase and IAA-induced elongation were similarly concentration dependent. Furthermore, IAA-induced H(+)-ATPase phosphorylation occurred in a tir1-1 afb2-3 double mutant, which is severely defective in auxin-mediated transcriptional regulation. In addition, α-(phenylethyl-2-one)-IAA, the auxin antagonist specific for the nuclear auxin receptor TIR1/AFBs, had no effect on IAA-induced H(+)-ATPase phosphorylation. These results suggest that the TIR1/AFB auxin receptor family is not involved in auxin-induced H(+)-ATPase phosphorylation. Our results define the activation mechanism of H(+)-ATPase by auxin during early-phase hypocotyl elongation; this is the long-sought-after mechanism that is central to the acid-growth theory.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takahashi
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Hayashi
authors.forename: Toshinori
authors.initials: T
authors.lastname: Kinoshita
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation; D044783:F-Box Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D018546:Hypocotyl / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D007210:Indoleacetic Acids / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D007976:Leupeptins / Q000494:pharmacology; D008387:Marine Toxins; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013912:Threonine / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D044783:F-Box Proteins; D007210:Indoleacetic Acids; D007976:Leupeptins; D008387:Marine Toxins; D010080:Oxazoles; D011956:Receptors, Cell Surface; C501405:TIR1 protein, Arabidopsis; C574628:alpha-(phenylethyl-2-oxo)indole-3-acetic acid; D019319:Okadaic Acid; D013912:Threonine; C030737:indoleacetic acid; C059041:calyculin A; D046988:Proteasome Endopeptidase Complex; D006180:Proton-Translocating ATPases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde