Hisako Koita

Nara Institute of Science and Technology, Ikuma, Nara, Japan

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Publications (2)10.55 Total impact

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    ABSTRACT: Since the woody plants are important bio-materials for paper, chemical and energy production, strategies for improvement of their properties are of considerable interest. We examined the expression of Eucalyptus camaldulensis transcription factor (TF) genes in xylem tissues using an oligo-microarray gene analysis technique. As a result, we isolated 21 TF genes related to xylem development. Following a functional investigation of 7 TFs in vitro, we selected the xylem TF gene EcHB1, which encodes a HD-Zip class II, for investigation as a transgene. EcHB1 expression was driven by the CaMV35S promoter in transgenic tobacco plants, which showed greater fiber length (≤20%) and plant height (≤50%) than wild-type plants. In addition, leaf, root and stem growth were significantly enhanced in the transgenic lines, which also had a lower acid-soluble lignin and hemicellulose content than wild-type. Our results indicate that metabolic flexibility might be involved in these improvements to xylem cell wall biosynthesis and that in addition to providing a growth advantage, such modifications may confer long-term structural integrity to the woody perennials.
    Plant Biotechnology 01/2009; 26(1):115-120. DOI:10.5511/plantbiotechnology.26.115 · 0.87 Impact Factor
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    ABSTRACT: OsRac1, one of the Rac/Rop family of small GTPases, plays important roles in defense responses, including a role in the production of reactive oxygen species mediated by NADPH oxidase. We have identified an effector of OsRac1, namely rice (Oryza sativa) cinnamoyl-CoA reductase 1 (OsCCR1), an enzyme involved in lignin biosynthesis. Lignin, which is polymerized through peroxidase activity by using H(2)O(2) in the cell wall, is an important factor in plant defense responses, because it presents an undegradable mechanical barrier to most pathogens. Expression of OsCCR1 was induced by a sphingolipid elicitor, suggesting that OsCCR1 participates in defense signaling. In in vitro interaction and two-hybrid experiments, OsRac1 was shown to bind OsCCR1 in a GTP-dependent manner. Moreover, the interaction of OsCCR1 with OsRac1 led to the enzymatic activation of OsCCR1 in vitro. Transgenic cell cultures expressing the constitutively active OsRac1 accumulated lignin through enhanced CCR activity and increased reactive oxygen species production. Thus, it is likely that OsRac1 controls lignin synthesis through regulation of both NADPH oxidase and OsCCR1 activities during defense responses in rice.
    Proceedings of the National Academy of Sciences 02/2006; 103(1):230-5. DOI:10.1073/pnas.0509875103 · 9.67 Impact Factor