Kati Hännikäinen

Publications (3)10.73 Total impact

• Article: Characterization of the alnumycin gene cluster reveals unusual gene products for pyran ring formation and dioxan biosynthesis.

  Terhi Oja, Kaisa Palmu, Hanna Lehmussola, Outi Leppäranta, Kati Hännikäinen, Jarmo Niemi, Pekka Mäntsälä, Mikko Metsä-Ketelä
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  ABSTRACT: Alnumycin is closely related to the benzoisochromanequinone (BIQ) polyketides such as actinorhodin. Exceptional structural features include differences in aglycone tailoring that result in the unique alnumycin chromophore and the existence of an unusual 4-hydroxymethyl-5-hydroxy-1,3-dioxan moiety. Cloning and sequencing of the alnumycin gene cluster from Streptomyces sp. CM020 revealed expected biosynthesis genes for polyketide assembly, but several genes encoding subsequent tailoring enzymes were highly atypical. Heterologous expression studies confirmed that all of the genes required for alnumycin biosynthesis resided within the sequenced clone. Inactivation of genes aln4 and aln5 showed that the mechanism of pyran ring formation differs from actinorhodin and granaticin pathways. Further inactivation studies identified two genes, alnA and alnB, involved in the synthesis and attachment of the dioxan moiety, and resulted in the production of the polyketide prealnumycin.
  Chemistry & Biology 11/2008; 15(10):1046-57. · 5.83 Impact Factor
• Source

  Available from: peerproject.eu

  Article: Diverse roles for chloroplast stromal and thylakoid-bound ascorbate peroxidases in plant stress responses.

  Saijaliisa Kangasjärvi, Anna Lepistö, Kati Hännikäinen, Mirva Piippo, Eeva-Maria Luomala, Eva-Mari Aro, Eevi Rintamäki
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  ABSTRACT: Photosynthetic light reactions comprise a significant source of hydrogen peroxide (H(2)O(2)) in illuminated leaves. APXs (ascorbate peroxidases) reduce H(2)O(2) to water and play an important role in the antioxidant system of plants. In the present study we addressed the significance of chloroplast APXs in stress tolerance and signalling in Arabidopsis thaliana. To this end, T-DNA (transfer DNA) insertion mutants tapx, sapx and tapx sapx, lacking the tAPX (thylakoid-bound APX), sAPX (stromal APX) or both respectively, were characterized. Photo-oxidative stress during germination led to bleaching of chloroplasts in sapx single-mutant and particularly in the tapx sapx double-mutant plants, whereas the greening process of wild-type and tapx plants was only partially impaired. Mature leaves of tapx sapx double mutants were also susceptible to short-term photo-oxidative stress induced by high light or methyl viologen treatments. After a 2-week acclimation period under high light or under low temperature, none of the mutants exhibited enhanced stress symptoms. Immunoblot analysis revealed that high-light-stress-acclimated tapx sapx double mutants compensated for the absence of tAPX and sAPX by increasing the level of 2-cysteine peroxiredoxin. Furthermore, the absence of tAPX and sAPX induced alterations in the transcriptomic profile of tapx sapx double-mutant plants already under quite optimal growth conditions. We conclude that sAPX is particularly important for photoprotection during the early greening process. In mature leaves, tAPX and sAPX are functionally redundant, and crucial upon sudden onset of oxidative stress. Moreover, chloroplast APXs contribute to chloroplast retrograde signalling pathways upon slight fluctuations in the accumulation of H(2)O(2) in chloroplasts.
  Biochemical Journal 07/2008; 412(2):275-85. · 4.90 Impact Factor
• Chapter: Chloroplastic NADPH Thioredoxin Reductase Mediates Photoperiod-Dependent Development of Leaves in Arabidopsis

  Anna Lepistö, Saijaliisa Kangasjärvi, Eeva-Maria Luomala, Kati Hännikäinen, Günter Brader, Eevi Rintamäki
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  ABSTRACT: Homozygous Plants Lacking Chloroplastic Nadph Thioredoxin Reductase (Ntrc) Showed Retarded Growth And A Pale Green Phenotype When Grown Under Short Day Conditions (8 H Light/16 H Dark). The Number Of Chloroplasts Per Mesophyll Cell And The Total Chlorophyll Content Per Leaf Area Were Significantly Reduced In Ntrc. Moreover, Mesophyll Cells Had Irregular Shapes And Their Size Was Remarkably Reduced, Density Of Stomata Had Increased, And Flowering And Senescence Were Significantly Delayed. Biochemical Analysis Revealed That The Pale Green Phenotype Of Ntrc Did Not Result From Deficiencies In The Accumulation Or Unction Of The Photosynthetic Membrane Protein Complexes Nor From Impaired Carboxylation CapaCity Of Rubisco. The Low Rate Of Photosynthetic Co2 Fixation Was More Likely To Have Been Caused By A Doubled Respiration Rate And By Unbalanced Transpiration Of The Ntrc Leaves. Interestingly, The Mutant Phenotype Was Less Distinct When Plants Were Grown Under Long Day Conditions Or Under Continuous Light. The Photoperiod-Dependent Modulation Of Ntrc Leaf Structure Was Associated With Hormonal Imbalance: Auxin Content In Young Ntrc Seedlings Grown In Short Day Conditions Was Diminished When Compared To Wild Type Plants.
  12/2007: pages 1303-1306;