title: The SAUR19 subfamily of SMALL AUXIN UP RNA genes promote cell expansion.
abstract: The plant hormone auxin controls numerous aspects of plant growth and development by regulating the expression of hundreds of genes. SMALL AUXIN UP RNA (SAUR) genes comprise the largest family of auxin-responsive genes, but their function is unknown. Although prior studies have correlated the expression of some SAUR genes with auxin-mediated cell expansion, genetic evidence implicating SAURs in cell expansion has not been reported. The Arabidopsis SAUR19, SAUR20, SAUR21, SAUR22, SAUR23, and SAUR24 (SAUR19-24) genes encode a subgroup of closely related SAUR proteins. We demonstrate that these SAUR proteins are highly unstable in Arabidopsis. However, the addition of an N-terminal GFP or epitope tag dramatically increases the stability of SAUR proteins. Expression of these stabilized SAUR fusion proteins in Arabidopsis confers numerous auxin-related phenotypes indicative of increased and/or unregulated cell expansion, including increased hypocotyl and leaf size, defective apical hook maintenance, and altered tropic responses. Furthermore, seedlings expressing an artificial microRNA targeting multiple members of the SAUR19-24 subfamily exhibit short hypocotyls and reduced leaf size. Together, these findings demonstrate that SAUR19-24 function as positive effectors of cell expansion. This regulation may be achieved through the modulation of auxin transport, as SAUR gain-of-function and loss-of-function seedlings exhibit increased and reduced basipetal indole-3-acetic acid transport, respectively. Consistent with this possibility, SAUR19-24 proteins predominantly localize to the plasma membrane.
authors.affiliation: Department of Plant Biology, University of Minnesota, St Paul, MN 55108, USA.
authors.forename: Angela K
authors.initials: AK
authors.lastname: Spartz
authors.forename: Sang H
authors.initials: SH
authors.lastname: Lee
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Wenger
authors.forename: Nathalie
authors.initials: N
authors.lastname: Gonzalez
authors.forename: Hironori
authors.initials: H
authors.lastname: Itoh
authors.forename: Dirk
authors.initials: D
authors.lastname: Inzé
authors.forename: Wendy A
authors.initials: WA
authors.lastname: Peer
authors.forename: Angus S
authors.initials: AS
authors.lastname: Murphy
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Overvoorde
authors.forename: William M
authors.initials: WM
authors.lastname: Gray
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D049108:Cell Enlargement; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D005810:Multigene Family; D059828:Plant Cells / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism; D055550:Protein Stability; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D008565:Membrane Proteins; D010937:Plant Growth Regulators; D011993:Recombinant Fusion Proteins; C086789:SAUR-AC1 protein, Arabidopsis