title: Phloem-associated auxin response maxima determine radial positioning of lateral roots in maize.
abstract: In Arabidopsis thaliana, lateral-root-forming competence of pericycle cells is associated with their position at the xylem poles and depends on the establishment of protoxylem-localized auxin response maxima. In maize, our histological analyses revealed an interruption of the pericycle at the xylem poles, and confirmed the earlier reported proto-phloem-specific lateral root initiation. Phloem-pole pericycle cells were larger and had thinner cell walls compared with the other pericycle cells, highlighting the heterogeneous character of the maize root pericycle. A maize DR5::RFP marker line demonstrated the presence of auxin response maxima in differentiating xylem cells at the root tip and in cells surrounding the proto-phloem vessels. Chemical inhibition of auxin transport indicated that the establishment of the phloem-localized auxin response maxima is crucial for lateral root formation in maize, because in their absence, random divisions of pericycle and endodermis cells occurred, not resulting in organogenesis. These data hint at an evolutionarily conserved mechanism, in which the establishment of vascular auxin response maxima is required to trigger cells in the flanking outer tissue layer for lateral root initiation. It further indicates that lateral root initiation is not dependent on cellular specification or differentiation of the type of vascular tissue.
authors.affiliation: Department of Plant Systems Biology, Integrative Plant Biology Division, VIB, Technologiepark 927, 9052 Ghent, Belgium.
authors.forename: Leentje
authors.initials: L
authors.lastname: Jansen
authors.forename: Ianto
authors.initials: I
authors.lastname: Roberts
authors.forename: Riet
authors.initials: R
authors.lastname: De Rycke
authors.forename: Tom
authors.initials: T
authors.lastname: Beeckman
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D015415:Biomarkers; D002454:Cell Differentiation; D002455:Cell Division; D048429:Cell Size; D002473:Cell Wall / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D018519:Meristem / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D052585:Phloem / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D010797:Phthalimides / Q000494:pharmacology; D059828:Plant Cells / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D052584:Xylem / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D003313:Zea mays / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism
chemical_list: D015415:Biomarkers; D007210:Indoleacetic Acids; D010797:Phthalimides; C002687:alpha-naphthylphthalamic acid