title: Primary root protophloem differentiation requires balanced phosphatidylinositol-4,5-biphosphate levels and systemically affects root branching.
abstract: Protophloem is a specialized vascular tissue in growing plant organs, such as root meristems. In Arabidopsis mutants with impaired primary root protophloem differentiation, brevis radix (brx) and octopus (ops), meristematic activity and consequently overall root growth are strongly reduced. Second site mutation in the protophloem-specific presumed phosphoinositide 5-phosphatase cotyledon vascular pattern 2 (CVP2), but not in its homolog CVP2-like 1 (CVL1), partially rescues brx defects. Consistent with this finding, CVP2 hyperactivity in a wild-type background recreates a brx phenotype. Paradoxically, however, while cvp2 or cvl1 single mutants display no apparent root defects, the root phenotype of cvp2 cvl1 double mutants is similar to brx or ops, although, as expected, cvp2 cvl1 seedlings contain more phosphatidylinositol-4,5-biphosphate. Thus, tightly balanced phosphatidylinositol-4,5-biphosphate levels appear essential for proper protophloem differentiation. Genetically, OPS acts downstream of phosphatidylinositol-4,5-biphosphate levels, as cvp2 mutation cannot rescue ops defects, whereas increased OPS dose rescues cvp2 cvl1 defects. Finally, all three mutants display higher density and accelerated emergence of lateral roots, which correlates with increased auxin response in the root differentiation zone. This phenotype is also created by application of peptides that suppress protophloem differentiation, clavata3/embryo surrounding region 26 (CLE26) and CLE45. Thus, local changes in the primary root protophloem systemically shape overall root system architecture.
authors: Department of Plant Molecular Biology, University of Lausanne, Biophore Building, Lausanne CH-1015, Switzerland.
authors: Antia
authors: A
authors: Rodriguez-Villalon
authors: Department of Plant Molecular Biology, University of Lausanne, Biophore Building, Lausanne CH-1015, Switzerland.
authors: Bojan
authors: B
authors: Gujas
authors: Swammerdam Institute for Life Sciences, Section Plant Physiology, University of Amsterdam, Amsterdam 1098 XH, The Netherlands.
authors: Ringo
authors: R
authors: van Wijk
authors: Swammerdam Institute for Life Sciences, Section Plant Physiology, University of Amsterdam, Amsterdam 1098 XH, The Netherlands.
authors: Teun
authors: T
authors: Munnik
authors: Department of Plant Molecular Biology, University of Lausanne, Biophore Building, Lausanne CH-1015, Switzerland christian.hardtke@unil.ch.
authors: Christian S
authors: CS
authors: Hardtke
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D052585:Phloem / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C581881:CLE45 protein, Arabidopsis; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; C487799:CVP2 protein, Arabidopsis; D010744:Phosphoric Monoester Hydrolases
keywords: Arabidopsis; Auxin; CLE peptide; CLE26; CLE45; Lateral roots; Phosphoinositides