title: Constitutive Expression of Arabidopsis SMALL AUXIN UP RNA19 (SAUR19) in Tomato Confers Auxin-Independent Hypocotyl Elongation.
abstract: The plant hormone indole-3-acetic acid (IAA or auxin) mediates the elongation growth of shoot tissues by promoting cell expansion. According to the acid growth theory proposed in the 1970s, auxin activates plasma membrane H+-ATPases (PM H+-ATPases) to facilitate cell expansion by both loosening the cell wall through acidification and promoting solute uptake. Mechanistically, however, this process is poorly understood. Recent findings in Arabidopsis (Arabidopsis thaliana) have demonstrated that auxin-induced SMALL AUXIN UP RNA (SAUR) genes promote elongation growth and play a key role in PM H+-ATPase activation by inhibiting PP2C.D family protein phosphatases. Here, we extend these findings by demonstrating that SAUR proteins also inhibit tomato PP2C.D family phosphatases and that AtSAUR19 overexpression in tomato (Solanum lycopersicum) confers the same suite of phenotypes as previously reported for Arabidopsis. Furthermore, we employ a custom image-based method for measuring hypocotyl segment elongation with high resolution and a method for measuring cell wall mechanical properties, to add mechanistic details to the emerging description of auxin-mediated cell expansion. We find that constitutive expression of GFP-AtSAUR19 bypasses the normal requirement of auxin for elongation growth by increasing the mechanical extensibility of excised hypocotyl segments. In contrast, hypocotyl segments overexpressing a PP2C.D phosphatase are specifically impaired in auxin-mediated elongation. The time courses of auxin-induced SAUR expression and auxin-dependent elongation growth were closely correlated. These findings indicate that induction of SAUR expression is sufficient to elicit auxin-mediated expansion growth by activating PM H+-ATPases to facilitate apoplast acidification and mechanical wall loosening.
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Angela K
authors.initials: AK
authors.lastname: Spartz
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Vai S
authors.identifier: 0000-0002-2941-8801
authors.initials: VS
authors.lastname: Lor
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Hong
authors.identifier: 0000-0002-8402-0468
authors.initials: H
authors.lastname: Ren
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Neil E
authors.identifier: 0000-0001-5393-7743
authors.initials: NE
authors.lastname: Olszewski
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Miller
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Guosheng
authors.initials: G
authors.lastname: Wu
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.).
authors.forename: Edgar P
authors.identifier: 0000-0002-6890-4765
authors.initials: EP
authors.lastname: Spalding
authors.affiliation: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108 (A.K.S., V.S.L., H.R., N.E.O., W.M.G.); and grayx051@umn.edu.|Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706 (N.D.M., G.W., E.P.S.) grayx051@umn.edu.
authors.forename: William M
authors.identifier: 0000-0002-1320-290X
authors.initials: WM
authors.lastname: Gray
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000235:genetics / Q000254:growth & development*; D030821:Plants, Genetically Modified; D000071636:Protein Phosphatase 2C / Q000235:genetics / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C000623004:SAUR19 protein, Arabidopsis; D049452:Green Fluorescent Proteins; D000071636:Protein Phosphatase 2C; D006180:Proton-Translocating ATPases