title: Identification of up-regulated genes in flag leaves during rice grain filling and characterization of OsNAC5, a new ABA-dependent transcription factor.
abstract: Rice is a poor source of micronutrients such as iron and zinc. To help clarify the molecular mechanisms that regulate metal mobilization from leaves to developing seeds, we conducted suppression subtractive hybridization analysis in flag leaves of two rice cultivars. Flag leaves are the major source of remobilized metals for developing seeds. We isolated 78 sequences up-regulated in flag leaves at the grain filling stage relative to the panicle exertion stage. Differential expression of selected genes (encoding 7 transport proteins, the OsNAS3 enzyme and the OsNAC5 transcription factor) was confirmed by quantitative RT-PCR. We show that OsNAC5 expression is up-regulated by natural (aging) and induced senescence processes (dark, ABA application, high salinity, cold and Fe-deficiency) and its expression is not affected in the presence of 6-benzylaminopurine (a senescence inhibitor) under dark-induced senescence. Salt induction of OsNAC5 expression is abolished by nicotinamide, an inhibitor of ABA effects. This result and the presence of cis-acting elements in the promoter region of the OsNAC5 gene suggest an ABA-dependent regulation. Using four different rice cultivars, we show that OsNAC5 up-regulation is higher and earlier in flag leaves and panicles of IR75862 plants, which have higher seed concentrations of Fe, Zn and protein. We suggest that OsNAC5 is a novel senescence-associated ABA-dependent NAC transcription factor and its function could be related to Fe, Zn and amino acids remobilization from green tissues to seeds.
authors.affiliation: Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, RS, Brazil.
authors.forename: Raul A
authors.initials: RA
authors.lastname: Sperotto
authors.forename: Felipe K
authors.initials: FK
authors.lastname: Ricachenevsky
authors.forename: Guilherme L
authors.initials: GL
authors.lastname: Duarte
authors.forename: Tatiana
authors.initials: T
authors.lastname: Boff
authors.forename: Karina L
authors.initials: KL
authors.lastname: Lopes
authors.forename: Edilena R
authors.initials: ER
authors.lastname: Sperb
authors.forename: Michael A
authors.initials: MA
authors.lastname: Grusak
authors.forename: Janette Palma
authors.initials: JP
authors.lastname: Fett
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D016922:Cellular Senescence / Q000187:drug effects; D018076:DNA, Complementary / Q000235:genetics; D003624:Darkness; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D015723:Gene Library; D000090463:Iron Deficiencies; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D009928:Organ Specificity / Q000235:genetics; D012275:Oryza / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D010937:Plant Growth Regulators / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D016415:Sequence Alignment; D013312:Stress, Physiological / Q000187:drug effects; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics*; D015032:Zinc / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D010937:Plant Growth Regulators; D010940:Plant Proteins; D014157:Transcription Factors; D000040:Abscisic Acid; D015032:Zinc
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