title: Phytoglobins Improve Hypoxic Root Growth by Alleviating Apical Meristem Cell Death.
abstract: Hypoxic root growth in maize (Zea mays) is influenced by the expression of phytoglobins (ZmPgbs). Relative to the wild type, suppression of ZmPgb1.1 or ZmPgb1.2 inhibits the growth of roots exposed to 4% oxygen, causing structural abnormalities in the root apical meristems. These effects were accompanied by increasing levels of reactive oxygen species (ROS), possibly through the transcriptional induction of four Respiratory Burst Oxidase Homologs TUNEL-positive nuclei in meristematic cells indicated the involvement of programmed cell death (PCD) in the process. These cells also accumulated nitric oxide and stained heavily for ethylene biosynthetic transcripts. A sharp increase in the expression level of several 1-aminocyclopropane synthase (ZmAcs2, ZmAcs6, and ZmAcs7), 1-aminocyclopropane oxidase (Aco15, Aco20, Aco31, and Aco35), and ethylene-responsive (ZmErf2 and ZmEbf1) genes was observed in hypoxic ZmPgb-suppressing roots, which overproduced ethylene. Inhibiting ROS synthesis with diphenyleneiodonium or ethylene perception with 1-methylcyclopropene suppressed PCD, increased BAX inhibitor-1, an effective attenuator of the death programs in eukaryotes, and restored root growth. Hypoxic roots overexpressing ZmPgbs had the lowest level of ethylene and showed a reduction in ROS staining and TUNEL-positive nuclei in the meristematic cells. These roots retained functional meristems and exhibited the highest growth performance when subjected to hypoxic conditions. Collectively, these results suggest a novel function of Pgbs in protecting root apical meristems from hypoxia-induced PCD through mechanisms initiated by nitric oxide and mediated by ethylene via ROS.
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
authors.forename: Mohamed M
authors.identifier: 0000-0002-6021-9202
authors.initials: MM
authors.lastname: Mira
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
authors.forename: Robert D
authors.identifier: 0000-0001-9577-1622
authors.initials: RD
authors.lastname: Hill
authors.affiliation: Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 stasolla@cc.umanitoba.ca.
authors.forename: Claudio
authors.initials: C
authors.lastname: Stasolla
mesh_terms: D016923:Cell Death / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D015536:Down-Regulation / Q000235:genetics; D005030:Ethylenes / Q000096:biosynthesis; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D018519:Meristem / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development*; D009569:Nitric Oxide / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development; D013997:Time Factors; D003313:Zea mays / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D005030:Ethylenes; D009861:Onium Compounds; D010940:Plant Proteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D009569:Nitric Oxide; C007517:diphenyleneiodonium; C036216:ethylene