Biomedical subjects

Takeshi Kanegae

Publications and source records attributed to Takeshi Kanegae.

4 recordsLinked to original sources

PubMed2006

A single chromoprotein with triple chromophores acts as both a phytochrome and a phototropin.

Plants sense their environmental light conditions by using three photoreceptors that absorb in the UV, blue/near UV, and red/far-red spectral ranges. These photoreceptors have specific chromophore components corresponding to their absorption spectra. Phytochrome, a red/far-red light receptor, has phytochromobilin as its chromophore, whereas the blue/near UV photoreceptors cryptochrome and phototropin have a pair of flavin derivatives. Plants use these various photoreceptors to assess the surrounding light environment. Phytochrome 3 (PHY3) is a red light receptor found in some ferns, which preferentially grow under weak light. PHY3 is composed of a phytochrome chromophore-binding domain in its N-terminal portion and an almost full-length phototropin in its C-terminal half. This unusual domain organization implies that two different light-sensing systems coexist in this single photoreceptor, although these light-sensing systems usually reside in independent photoreceptors. Here, we show that PHY3 acts as a dual-channel photoreceptor that possesses both the red light-sensing system of phytochrome and the blue light-sensing system of phototropin. Furthermore, red- and blue-light signals perceived by PHY3 are processed synergistically within this single chromoprotein. These unusual properties might confer an enhanced light sensitivity on PHY3, allowing ferns to grow under a low-light canopy.

Adiantum↗

PubMed2004

DNA interference: a simple and efficient gene-silencing system for high-throughput functional analysis in the fern adiantum.

RNA interference (RNAi) has become a powerful tool for determining gene function and is used in a wide variety of organisms. Since it is necessary to generate double-stranded RNA (dsRNA) as an inducer for RNAi, preparation of RNAi-inducing constructs is somewhat cumbersome and time consuming, especially for the thousands of genes used in a genome-wide analysis. To overcome these problems, we have developed a more convenient gene-silencing method in the fern Adiantum using double-stranded DNA (dsDNA) as a model system for functional analysis in plants. Delivery of dsDNA fragments homologous to an endogenous gene into gametophytic cells can induce sequence-specific gene silencing. As it only requires dsDNA fragments homologous to a target gene, PCR-amplified fragments are enough to trigger gene silencing. Maximum gene silencing efficiencies of >90% have been achieved for transformed plants. In addition, simultaneous transfer of dsDNA fragments corresponding to multiple genes still has a silencing effect for individual genes. We term this approach 'DNA interference'.

Adiantum↗

PubMed2003

Chloroplast unusual positioning1 is essential for proper chloroplast positioning.

The intracellular distribution of organelles is a crucial aspect of effective cell function. Chloroplasts change their intracellular positions to optimize photosynthetic activity in response to ambient light conditions. Through screening of mutants of Arabidopsis defective in chloroplast photorelocation movement, we isolated six mutant clones in which chloroplasts gathered at the bottom of the cells and did not distribute throughout cells. These mutants, termed chloroplast unusual positioning (chup), were shown to belong to a single genetic locus by complementation tests. Observation of the positioning of other organelles, such as mitochondria, peroxisomes, and nuclei, revealed that chloroplast positioning and movement are impaired specifically in this mutant, although peroxisomes are distributed along with chloroplasts. The CHUP1 gene encodes a novel protein containing multiple domains, including a coiled-coil domain, an actin binding domain, a Pro-rich region, and two Leu zipper domains. The N-terminal hydrophobic segment of CHUP1 was expressed transiently in leaf cells of Arabidopsis as a fusion protein with the green fluorescent protein. The fusion protein was targeted to envelope membranes of chloroplasts in mesophyll cells, suggesting that CHUP1 may localize in chloroplasts. A glutathione S-transferase fusion protein containing the actin binding domain of CHUP1 was found to bind F-actin in vitro. CHUP1 is a unique gene identified that encodes a protein required for organellar positioning and movement in plant cells.

Amino Acid Sequence↗

PubMed2003

Responses of ferns to red light are mediated by an unconventional photoreceptor.

Efficient photosynthesis is essential for plant survival. To optimize photosynthesis, plants have developed several photoresponses. Stems bend towards a light source (phototropism), chloroplasts move to a place of appropriate light intensity (chloroplast photorelocation) and stomata open to absorb carbon dioxide. These responses are mediated by the blue-light receptors phototropin 1 (phot1) and phototropin 2 (phot2) in Arabidopsis (refs 1-5). In some ferns, phototropism and chloroplast photorelocation are controlled by red light as well as blue light. However, until now, the photoreceptor mediating these red-light responses has not been identified. The fern Adiantum capillus-veneris has an unconventional photoreceptor, phytochrome 3 (phy3), which is a chimaera of the red/far-red light receptor phytochrome and phototropin. We identify here a function of phy3 for red-light-induced phototropism and for red-light-induced chloroplast photorelocation, by using mutational analysis and complementation. Because phy3 greatly enhances the sensitivity to white light in orienting leaves and chloroplasts, and PHY3 homologues exist among various fern species, this chimaeric photoreceptor may have had a central role in the divergence and proliferation of fern species under low-light canopy conditions.

Adiantum↗