title: Response to zinc deficiency of two rice lines with contrasting tolerance is determined by root growth maintenance and organic acid exudation rates, and not by zinc-transporter activity.
abstract: *Zinc (Zn)-deficient soils constrain rice (Oryza sativa) production and cause Zn malnutrition. The identification of Zn-deficiency-tolerant rice lines indicates that breeding might overcome these constraints. Here, we seek to identify processes underlying Zn-deficiency tolerance in rice at the physiological and transcriptional levels. *A Zn-deficiency-tolerant line RIL46 acquires Zn more efficiently and produces more biomass than its nontolerant maternal line (IR74) at low [Zn](ext) under field conditions. We tested if this was the result of increased expression of Zn(2+) transporters; increased root exudation of deoxymugineic acid (DMA) or low-molecular-weight organic acids (LMWOAs); and/or increased root production. Experiments were performed in field and controlled environment conditions. *There was little genotypic variation in transcript abundance of Zn-responsive root Zn(2+)-transporters between the RIL46 and IR74. However, root exudation of DMA and LMWOA was greater in RIL46, coinciding with increased root expression of putative ligand-efflux genes. Adventitious root production was maintained in RIL46 at low [Zn](ext), correlating with altered expression of root-specific auxin-responsive genes. *Zinc-deficiency tolerance in RIL46 is most likely the result of maintenance of root growth, increased efflux of Zn ligands, and increased uptake of Zn-ligand complexes at low [Zn](ext); these traits are potential breeding targets.
authors.affiliation: Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1 Ohwashi, 305-8686 Tsukuba, Japan.
authors.forename: Basuki
authors.initials: B
authors.lastname: Widodo
authors.forename: Martin R
authors.initials: MR
authors.lastname: Broadley
authors.forename: Terry
authors.initials: T
authors.lastname: Rose
authors.forename: Michael
authors.initials: M
authors.lastname: Frei
authors.forename: Juan
authors.initials: J
authors.lastname: Pariasca-Tanaka
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yoshihashi
authors.forename: Michael
authors.initials: M
authors.lastname: Thomson
authors.forename: John P
authors.initials: JP
authors.lastname: Hammond
authors.forename: Alessio
authors.initials: A
authors.lastname: Aprile
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Close
authors.forename: Abdelbagi M
authors.initials: AM
authors.lastname: Ismail
authors.forename: Matthias
authors.initials: M
authors.lastname: Wissuwa
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D002264:Carboxylic Acids / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D007178:Inbreeding; D008903:Minerals / Q000378:metabolism; D008954:Models, Biological; D008970:Molecular Weight; D020411:Oligonucleotide Array Sequence Analysis; D012275:Oryza / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015032:Zinc / Q000172:deficiency* / Q000494:pharmacology
chemical_list: D002264:Carboxylic Acids; D002352:Carrier Proteins; D008903:Minerals; D010940:Plant Proteins; D012333:RNA, Messenger; C017800:zinc-binding protein; D001383:Azetidinecarboxylic Acid; C052864:2'-deoxymugineic acid; D015032:Zinc