title: Abscisic acid rescues the root meristem defects of the Medicago truncatula latd mutant.
abstract: The LATD gene of the model legume, Medicago truncatula, is required for the normal function of three meristems, i.e. the primary root, lateral roots and nitrogen-fixing nodules. In latd mutants, primary root growth eventually arrests, resulting in a disorganized root tip lacking a presumptive meristem and root cap columella cells. Lateral root organs are more severely affected; latd lateral roots and nodules arrest immediately after emerging from the primary root, and reveal a lack of organization. Here we show that the plant hormone, abscisic acid (ABA), can rescue the latd root, but not nodule, meristem defects. Growth on ABA is sufficient to restore formation of small, cytoplasm-rich cells in the presumptive meristem region, rescue meristem organization and root growth and formation of root cap columella cells. In contrast, inhibition of ethylene synthesis or signaling fails to restore latd primary root growth. We find that latd mutants have normal levels of ABA, but exhibit reduced sensitivity to the hormone in two other ABA-dependent processes: seed germination and stomatal closure. Together, these observations demonstrate that the latd mutant is defective in the ABA response and indicate a role for LATD-dependent ABA signaling in M. truncatula root meristem function.
authors.affiliation: Department of Plant Biology, University of Vermont, Burlington, VT 05405-0086, USA. Yan.Liang@uvm.edu
authors.forename: Yan
authors.initials: Y
authors.lastname: Liang
authors.forename: David M
authors.initials: DM
authors.lastname: Mitchell
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Harris
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D018525:Germination / Q000502:physiology; D046913:Medicago truncatula / Q000235:genetics / Q000254:growth & development*; D018519:Meristem / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology; D016962:Sinorhizobium meliloti
chemical_list: D010937:Plant Growth Regulators; D010940:Plant Proteins; D000040:Abscisic Acid