title: Asymmetric localizations of the ABC transporter PaPDR1 trace paths of directional strigolactone transport.
abstract: Strigolactones, first discovered as germination stimulants for parasitic weeds [1], are carotenoid-derived phytohormones that play major roles in inhibiting lateral bud outgrowth and promoting plant-mycorrhizal symbiosis [2-4]. Furthermore, strigolactones are involved in the regulation of lateral and adventitious root development, root cell division [5, 6], secondary growth [7], and leaf senescence [8]. Recently, we discovered the strigolactone transporter Petunia axillaris PLEIOTROPIC DRUG RESISTANCE 1 (PaPDR1), which is required for efficient mycorrhizal colonization and inhibition of lateral bud outgrowth [9]. However, how strigolactones are transported through the plant remained unknown. Here we show that PaPDR1 exhibits a cell-type-specific asymmetric localization in different root tissues. In root tips, PaPDR1 is co-expressed with the strigolactone biosynthetic gene DAD1 (CCD8), and it is localized at the apical membrane of root hypodermal cells, presumably mediating the shootward transport of strigolactone. Above the root tip, in the hypodermal passage cells that form gates for the entry of mycorrhizal fungi, PaPDR1 is present in the outer-lateral membrane, compatible with its postulated function as strigolactone exporter from root to soil. Transport studies are in line with our localization studies since (1) a papdr1 mutant displays impaired transport of strigolactones out of the root tip to the shoot as well as into the rhizosphere and (2) DAD1 expression and PIN1/PIN2 levels change in plants deregulated for PDR1 expression, suggestive of variations in endogenous strigolactone contents. In conclusion, our results indicate that the polar localizations of PaPDR1 mediate directional shootward strigolactone transport as well as localized exudation into the soil.
authors: Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland.
authors: Joëlle
authors: J
authors: Sasse
authors: Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria.
authors: Sibu
authors: S
authors: Simon
authors: Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland.
authors: Christian
authors: C
authors: Gübeli
authors: Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland.
authors: Guo-Wei
authors: GW
authors: Liu
authors: Wageningen UR, Wageningen University, 6708 PB Wageningen, the Netherlands.
authors: Xi
authors: X
authors: Cheng
authors: Institute of Science and Technology Austria, 3400 Klosterneuburg, Austria.
authors: Jiří
authors: J
authors: Friml
authors: Wageningen UR, Wageningen University, 6708 PB Wageningen, the Netherlands.
authors: Harro
authors: H
authors: Bouwmeester
authors: Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland.
authors: Enrico
authors: E
authors: Martinoia
authors: Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland. Electronic address: lorenzo.borghi@uzh.ch.
authors: Lorenzo
authors: L
authors: Borghi
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D018525:Germination / Q000187:drug effects*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007783:Lactones / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D031672:Orobanche / Q000378:metabolism / Q000502:physiology*; D032306:Petunia / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D018528:ATP-Binding Cassette Transporters; D007783:Lactones; D049452:Green Fluorescent Proteins; C483518:strigol