title: Auxin-responsive DR5 promoter coupled with transport assays suggest separate but linked routes of auxin transport during woody stem development in Populus.
abstract: Polar auxin transport (PAT) is a major determinant of plant morphology and internal anatomy with important roles in vascular patterning, tropic growth responses, apical dominance and phyllotactic arrangement. Woody plants present a highly complex system of vascular development in which isolated bundles of xylem and phloem gradually unite to form concentric rings of conductive tissue. We generated several transgenic lines of hybrid poplar (Populus tremula x alba) with the auxin-responsive DR5 promoter driving GUS expression in order to visualize an auxin response during the establishment of secondary growth. Distinct GUS expression in the cambial zone and developing xylem-side derivatives supports the current view of this tissue as a major stream of basipetal PAT. However, we also found novel sites of GUS expression in the primary xylem parenchyma lining the outer perimeter of the pith. Strands of primary xylem parenchyma depart the stem as a leaf trace, and showed GUS expression as long as the leaves to which they were connected remained attached (i.e., until just prior to leaf abscission). Tissue composed of primary xylem parenchyma strands contained measurable levels of free indole-3-acetic acid (IAA) and showed basipetal transport of radiolabeled auxin ((3)H-IAA) that was both significantly faster than diffusion and highly sensitive to the PAT inhibitor NPA. Radiolabeled auxin was also able to move between the primary xylem parenchyma in the interior of the stem and the basipetal stream in the cambial zone, an exchange that was likely mediated by ray parenchyma cells. Our results suggest that (a) channeling of leaf-derived IAA first delineates isolated strands of pre-procambial tissue but then later shifts to include basipetal transport through the rapidly expanding xylem elements, and (b) the transition from primary to secondary vascular development is gradual, with an auxin response preceding the appearance of a unified and radially-organized vascular cambium.
authors: Department of Botany, Connecticut College, New London, Connecticut, United States of America. rspicer@conncoll.edu
authors: Rachel
authors: R
authors: Spicer
authors: Tracy
authors: T
authors: Tisdale-Orr
authors: Christian
authors: C
authors: Talavera
mesh_terms: D001681:Biological Assay / Q000379:methods*; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D004058:Diffusion; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005966:Glucuronidase / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development; D018547:Plant Stems / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D058526:Plant Vascular Bundle / Q000187:drug effects / Q000378:metabolism; D030821:Plants, Genetically Modified; D032107:Populus / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D011401:Promoter Regions, Genetic; D014316:Tritium / Q000378:metabolism; D014934:Wood / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*
chemical_list: D007210:Indoleacetic Acids; D014316:Tritium; D005966:Glucuronidase
references: Anal Biochem. 2008 Jan 15;372(2):177-88
references: 17889819
references: Plant Biol (Stuttg). 2004 Jan-Feb;6(1):22-9
references: 15095131
references: Plant Cell Environ. 2006 Aug;29(8):1519-31
references: 16898015
references: Plant J. 2001 Nov;28(4):465-74
references: 11737783
references: Nat Protoc. 2009;4(4):437-51
references: 19282849
references: Front Plant Sci. 2012 Feb 07;3:17
references: 22645571
references: FEBS Lett. 2006 Feb 13;580(4):1094-102
references: 16359667
references: New Phytol. 2004 Oct;164(1):157-164
references: 33873480
references: Science. 2008 Jun 20;320(5883):1610
references: 18566279
references: Planta. 1984 May;161(3):207-15
references: 24253645
references: Plant Cell. 1997 Nov;9(11):1963-71
references: 9401121
references: Plant Cell Environ. 2007 Aug;30(8):934-43
references: 17617821
references: Nat Protoc. 2010 Sep;5(10):1609-18
references: 20885372
references: Plant Physiol. 2001 Apr;125(4):2029-39
references: 11299382
references: Plant J. 2007 Nov;52(3):499-511
references: 17825053
references: Plant Cell. 2004 Sep;16(9):2278-92
references: 15316113
references: Plant Cell Rep. 2000 Jan;19(3):315-320
references: 30754915
references: Plant Mol Biol. 1998 Nov;38(5):861-73
references: 9862502
references: Planta. 1977 Jan;134(3):241-9
references: 24419777
references: Cold Spring Harb Perspect Biol. 2010 Jan;2(1):a001511
references: 20182604
references: Curr Biol. 2011 Jun 7;21(11):917-26
references: 21620702
references: Planta. 1986 Sep;168(3):377-80
references: 24232147
references: Plant Physiol. 2004 May;135(1):212-20
references: 15122024
references: Plant J. 2004 Oct;40(2):173-87
references: 15447645
references: Genes Dev. 2006 Oct 15;20(20):2902-11
references: 17043314
references: Plant Physiol. 1998 May;117(1):113-21
references: 9576780
references: New Phytol. 2010 May;186(3):577-92
references: 20522166
references: Planta. 2007 Jul;226(2):361-8
references: 17308928
references: Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13630-5
references: 19666540
references: Science. 1958 Oct 31;128(3331):1084-5
references: 17741838
references: Proc Natl Acad Sci U S A. 1996 Aug 20;93(17):9282-6
references: 11607701
references: Curr Biol. 2011 Jun 7;21(11):927-32
references: 21620705
references: Cold Spring Harb Perspect Biol. 2010 Mar;2(3):a001552
references: 20300209
references: Plant Physiol. 1997 Oct;115(2):577-585
references: 12223825
references: Planta. 1972 Dec;107(4):301-14
references: 24477480
references: Genes Dev. 2006 Apr 15;20(8):1015-27
references: 16618807
references: Plant Physiol. 1966 Apr;41(4):673-82
references: 16656304
references: Science. 1988 Jul 15;241(4863):346-9
references: 17734864
references: Plant Cell. 2005 Apr;17(4):1090-104
references: 15772288
references: EMBO J. 1987 Dec 20;6(13):3901-7
references: 3327686
references: Trends Plant Sci. 2005 Apr;10(4):170-7
references: 15817418
references: Trends Plant Sci. 2002 May;7(5):193-5
references: 11992820
references: Cold Spring Harb Perspect Biol. 2010 Jan;2(1):a001594
references: 20182605
references: Plant Physiol. 1990 Aug;93(4):1295-302
references: 16667616
references: Proc Natl Acad Sci U S A. 1968 Apr;59(4):1089-96
references: 16591628
references: Nature. 2005 Jan 6;433(7021):39-44
references: 15635403
references: Plant Physiol. 1986 Jan;80(1):14-9
references: 16664570
references: Science. 1998 Dec 18;282(5397):2226-30
references: 9856939
references: Nature. 2005 May 26;435(7041):441-5
references: 15917797
references: J Theor Biol. 2002 May 21;216(2):147-58
references: 12079368
references: Proc Natl Acad Sci U S A. 2003 Aug 19;100(17):10096-101
references: 12909722
references: Science. 2004 Oct 29;306(5697):862-5
references: 15514156
references: Plant Physiol. 1994 Oct;106(2):469-476
references: 12232343