title: Nitric oxide participates in plant flowering repression by ascorbate.
abstract: In Oncidium, redox homeostasis involved in flowering is mainly due to ascorbic acid (AsA). Here, we discovered that Oncidium floral repression is caused by an increase in AsA-mediated NO levels, which is directed by the enzymatic activities of nitrate reductase (NaR) and nitrite reducatase (NiR). Through Solexa transcriptomic analysis of two libraries, 'pseudobulb with inflorescent bud' (PIB) and 'pseudobulb with axillary bud' (PAB), we identified differentially expressed genes related to NO metabolism. Subsequently, we showed a significant reduction of NaR enzymatic activities and NO levels during bolting and blooming stage, suggesting that NO controlled the phase transition and flowering process. Applying AsA to Oncidium PLB (protocorm-like bodies) significantly elevated the NO content and enzyme activities. Application of sodium nitroprusside (-NO donor) on Arabidopsis vtc1 mutant caused late flowering and expression level of flowering-associated genes (CO, FT and LFY) were reduced, suggesting NO signaling is vital for flowering repression. Conversely, the flowering time of noa1, an Arabidopsis NO-deficient mutant, was not altered after treatment with L-galacturonate, a precursor of AsA, suggesting AsA is required for NO-biosynthesis involved in the NO-mediated flowering-repression pathway. Altogether, Oncidium bolting is tightly regulated by AsA-mediated NO level and downregulation of transcriptional levels of NO metabolism genes.
authors.affiliation: Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Rajendran
authors.initials: R
authors.lastname: Senthil Kumar
authors.affiliation: Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Chin-Hui
authors.initials: CH
authors.lastname: Shen
authors.affiliation: Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Pei-Yin
authors.initials: PY
authors.lastname: Wu
authors.affiliation: Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Subbiah
authors.initials: S
authors.lastname: Suresh Kumar
authors.affiliation: Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Moda Sang
authors.initials: MS
authors.lastname: Hua
authors.affiliation: Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Kai-Wun
authors.initials: KW
authors.lastname: Yeh
mesh_terms: D001205:Ascorbic Acid / Q000008:administration & dosage*; D035264:Flowers / Q000235:genetics / Q000254:growth & development*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D009569:Nitric Oxide / Q000502:physiology*
chemical_list: D009569:Nitric Oxide; D001205:Ascorbic Acid