Hironao Kataoka, D.Sc., Associate Professor
E-mail: kataoka@ige.tohoku.ac.jp
last updated 090807
Born
in Shiga, near Kyoto in 1947. Graduated Kobe Univ. (Faculty of Science
, Department of Biology) in 1969. After moving to Osaka Univ. as a graduate
student, I learnt first from Dr. Masashi Tazawa water
relation and ionic regulation of Characean internodal cells . Then I was
attracted by Vaucheria which Prof. Noburo Kamiya
suggested me to use as an experimental material for studying tip growth
and cell wall regeneration. He collected some Vaucheria specimen
from a stream around George Lake near Albany, NY in 1970. I succeeded
axenic culture of Vaucheria and analyzed growth kinetics of the
cell wall at the apical tip-growing hemispherical dome, and at a moment
when I found a bluelight-dependent phototropism and cytomorphogenesis
in 1974, I became a photobiologist. Since then Vaucheria
has been my most important teacher of biology.
I took Ph.D (=D. Sc. in Japan) in 1975, spent 15 months as a PDF (JSPS)
at Prof. Kamiya's lab. in Osaka Univ., and came to Sendai (Institute for
Agricultural Research) in 1976 as a technician. After several reorganizations,
formerly Institute of Genetic Ecology was further --I hope finally --
reorganized in April 2001 to Graduate School of Life Scineces, Tohoku
University.
I have studied mainly phototropism and photocytomorphogenesis of Vaucheria. My research field is, however, extending to phylogeny and ecology from classic plant cell physiology, photobiology, and biophysics. I am lucky enough because I and my group can discovered the photoreceptor AUREOCHROME (see below) for the photomorphogenetic response of Vaucheria which I found by myself more than 30 years ago and I was able to continue this research throughout.
L: Vaucheria frigida grown in the Botanical Garden of Tohoku University; M: Blue light (BL) responses of Vaucheria. 1) positive phototropism; 2) negative phototropism; 3) BL-induced branching; 4) apical expansion; 5) Red light is quite inert. R: Accumulation of nuclei and newly gene expression is necessary for branch induction. Another photoreception system may mediate the chloroplast accumulation in the BL-irradiated region.
We have recently discovered quite novel bluelight receptor in Vaucheria（PNAS 104:19625-19630) . Although phototropism and photomorphogenesis of Vaucheria are induced by bluelight, Vaucheria does not have the photoreceptor of green plants, PHOTOTROPIN (phot). We thus looked for photoreceptors in mRNA of Vaucheria frigida and cloned several candidates of photoreceptors that have each one basic-region leucine-zipper (bZIP) domain and one light-oxygen-voltage (LOV) domain, instead of PHOTOTROPIN. At least one of these bZIP-LOV protein forms a cystenyl photoadduct when it absorbs bluelight, and this photoadduct was broken gradually (~5 min) in subsequent darkness; this strongly indicates that this serves as a blue light photoreceptor. This molecular species of bZIP-LOV protein was further found to be a bluelight-activated transcription regulator that binds to a target DNA sequence, TGACGT. Performing knock-down experiment by means of RNAi, we found that this bZIP-LOV protein serves as photoreceptors in Vaucheria either for the bluelight-induced branching or for supression of sexual development.
L: Structure of AUREOCHROME1 & AUREOCHROME2. When the BL-sensing domain LOV absorbs BL, Aureo1 binds specifically to the target sequence TGACGT of DNA at its bZIP domain.
R: Hypothesis for the role of AUREOCHROMEs in the BL-induced branching of Vaucheria. For detail, see Takahashi et al. (PNAS 104:19625-19630.
L: Fucus distichus (left) and Laminaria japonica (right). These brown algae (Phaeophyta) belong to Stramenopile and they posses AUREOCHROMEs. Photos, taken at Muroran, Hokkaido in 2006. R: Phylogenetic tree of eukaryotes. Stramenopiles are believed to be formed by secondary endosymbiosis with red algal symbiont and ancestral host eukaryote.
We named this photoreceptor protein AUREOCHROME, because several orthologs of this photoreceptor have been found in other photosynthetic stramenopiles, such as in Fucus (brown algae), diatoms and Chrysophycean algae. Photosynthetic stramenopiles, to which Vaucheria, diatoms, brown algae and Chrysophyceae etc. are belonging, are called "yellow plants". Thus, AUREOCHROME is probably the common bluelight receptor of yelow plants. Yellow plants do not have phototropin. On the other hand, any green plants does not have AUREOCHROME.
Comparing to "green plants", which includes land plants, Characeae and green algae, yellow plants are phylogenicaly quite unique groups. Origin of stramenopiles' chloroplasts is believed to be an eulkaryote, red alga. Stramenopiles are therefore one of the secondary endosymbiotic algae. AUREOCHROME may play common and essential roles in growth and development of stramenopiles. To our PNAS paper, Aba Losi and Wolfgang Gärtner wrote a nice commentary, entitiled " Shedding (blue) light on algal gene expression" (PNAS 105: 7-8, 2008). Peter Hegemann also introduce our AUREOCHROME in his review (Ann. Rev. plant Biol. 2008, 59:167-189). In November 2008, Chris Bowler et al. (Nature 456:239-244)fully analyzed the genome of a pennate diatom, Phaeodactylum tricornatum and found that there are three AUREOCHROME orthologs in the genome, one of which has a unique structure in that the positions of bZIP- and LOV domains are exchanged. Nevertheless, nothing is known about the function of AUREOCHROMEs of the diatom. Our most recent paper, dealing with the phylogenetic trees of aureochrome orthologues has just been published in Planta (2009). In this paper, we described interesting findings that 1) all the aureocrome sequences so far determined directly from cDNA or detected in the genomic databases are placed in a single clade, and that 2) the LOV domains of aureochromes look more similer to those of LOV2 domains of the phototropins, the common BL-receptor for green plants. The latter may indicate that the ancestral phototropin might have only one LOV domain. Presently widely distributing phototropins in green plants may gain another LOV domains (LOV1) as an attenuator to reduce sensitivity to strong sunlight during its evolution.
Since many prokaryotes have LOV domains as functional BL sensor, the eukaryotic LOV BL-sensors, such as aureochromes, phototropins, fungal BL receptors, VVD or WC1, etc must share their origins in prokaryotes.
However, I have to retire Tohoku University next (2010) March. And I nave no appointment for the researching place afterward. So, I cannot accept student anymore. I hope someone having being interested in and enthusiasm would continue the research of aureochrome. Also, please contact me if you want to provide me a place for 2-3 years to further extending researches on AUREOCHROME.
Research
projects of our group are:
I. Analyses of photophysiological responses of
tip-growing cells.
II.
Biology of coenocytes, esp. Vaucheria and Bryopsis.
For
more detail, go to: Biology
of Coenocytes, and
Phototropism and photomorphogenesis
of Vaucheria.
Publication list
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