(Figures) Gamma tubulin on cortical microtubules (1). Gamma tubulin localized on a preexisted microtubule (2). Nicotiana benthamiana (3) in which the gamma tubulin gene is silenced forms malformed leaves (4).
The Hasebe laboratory
Current projects
1. Phylogeny of land plants
Phylogeny of representative lineages in land plants are investigated
using nucleotide and amino acid sequences. We are interested in phylogenetic
relationships of major groups, such as extant gymnosperms (Hasebe et al. 1992),
ferns (Hasebe et al. 1994, 1995), and bryophytes (Nishiyama et al. 2004) , as
well as those of several specific taxa (Acer, Aster, Coriaria, Drosera, Dendrobiinae,
Typhonium and more).
extant gymnosperms
Hasebe, M., Kofuji, R., Ito, M., Kato, M., Iwatsuki, K. and
Ueda, K. 1992. Phylogeny of gymnosperms inferred from rbcL gene sequences. Bot.
Mag. Tokyo 105: 673-679.
extant ferns
Hasebe, M., Omori, T., Nakazawa, M., Sano, T., Kato, M. and
Iwatsuki, K. 1994. rbcL gene sequences provide evidence for the evolutionary
lineages of leptosporangiate ferns. Proc. Natl. Acad. Sci. USA 91: 5730-5734.
Hasebe, M., Wolf, P.G., Pryer, K.M., Ueda, K., Ito, M., Sano, R., Gastony,
G.J., Yokoyama, J., Manhart, J.R., Murakami, N., Crane, E.H., Haufler, C.H.
and Hauk, W.D. 1995. A global analysis of fern phylogeny based on rbcL nucleotide
sequences.
American Fern Journal 35: 134-181.
extant bryophytes
Nishiyama, T., Wolf, P.G., Kugita, M., Sinclair, R.B., Sugita,
M., Sugiura, C., Wakasugi, T., Yamada, K., Yoshinaga, K. Yamaguchi, K., Ueda,
K., and Hasebe, M. 2004. Chloroplast phylogeny indicates that bryophytes are
monophyletic. Mol. Biol. Evol. 21: 1813-1819.
2. Origin and evolution of the
chloroplast: focusing on chloroplast movement
The first green alga cell evolved via symbiosis between an ancestral
non-photosynthetic eukaryote and a cyanobacterium. Cyanobacteria now exist as
chloroplasts in the host cell. The factors and mechanisms of chloroplast movement
are being investigated to reveal the molecular mechanisms used to "domesticate"
cyanobacteria as organelles.
3. Origin and evolution of the plant cell: focucing on microtubules (Senior researcher: Takashi Murata)
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The most prominent difference between plant and animal cells is that plant
cells have a cell wall and do not move during development. Therefore, the
plane of cell division and the direction of cell elongation, which are regulated
by cortical microtubules, determine the morphology of differentiated tissues
and organs. Gamma tubulin is a protein that is essential for the formation
of microtubules in animal cells. Microtubules are initiated at the centrosome
in animal cells, but places where microtubules are initiated in plan cells,
which lack the centrosome, were unknown. We recently found that new microtubules
are initiated on the preexisted microtubules as branches, and cortical microtubules
are organized without centrosome. To explore how such differences between
animal and plant cells evolved, we focus on finding a protein complex expected
to be localized at the branching point. (Figures) Gamma tubulin on cortical microtubules (1). Gamma tubulin localized on a preexisted microtubule (2). Nicotiana benthamiana (3) in which the gamma tubulin gene is silenced forms malformed leaves (4). |
Murata, T., Sonobe, S., Baskin, T. I., Hyodo, S., Hasezawa, S., Nagata, T., Horio, T., and Hasebe, M. Microtubules are nucleated on extant microtubules via gamma-tubulin in plant cortical arrays. submitted.
4. Evolution from unicellular to multicellular organisms
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The first evolutionary step from unicellular to multicellular organisms
is to form two different cells from a single cell via asymmetric cell
division. The first cell division of a protoplast isolated from the protonemata
of the moss Physcomitrella patens is asymmetric and gives rise
to an apical meristematic cell and a differentiated non-meristematic cell.
We screened genes involved in asymmetric cell division by large-scale
overexpression screening of 15000 Physcomitrella full-length cDNAs. Approximately
60 candidate genes that caused defects in asymmetric cell division by
overexpression were isolated, and experiments to determine their cellular
localization and RNAi experiments are currently in progress. |
Fujita, T., Nishiyama, T., Hiwatashi, Y. and Hasebe, M. 2003. Gene tagging, gene- and enhancer-trap systems, and full-length cDNA overexpression in Physcomitrella patens. p. 111-132. In New Frontiers in Bryology:Physiology, Molecular Biology & Applied Genomics (eds. by Wood, AJ., Oliver, MJ. and Cove, DJ.), Kluwer Academic Publishers, Netherlands.
5. Evolution of body plans in plants
Green plants landed more than 400 million years ago. The common ancestors of land plants are inferred to have been haploid-dominant. The mosses, which is the most basal lineage, have haploid-dominant life cycle, while the pteridophytes and seed plants are diploid-dominant. The mosses form shoot system in their haploid generation, while vascular plants (pteriodphytes and seed plants) form in diploid generation. There are two alternative hypotheses. One is that genes used in the diploid body of vascular plants were recruited from the genes used in the haploid body of their ancestors during the evolution of land plants. The other is that the body plan in diploid generation might have evolved de novo. We aim to explore the origin and evolution of molecular mechanisms underlying land plant body plan.
(5-1) Comparison of whole genomes
To assess the origin and evolution of diploid body plan in land plants, we constructed an expressed sequence tag (EST) library of the moss Physcomitrella patens, and compared the moss transcriptome to the genome of Arabidopsis thaliana. Furthermore, the whole genome sequencing project is on going under DOE Joint Genome Project and MEXT Grant for Priority Area Comparative Genomics.
Nishiyama*, T., Fujita*, T., Shin-I, T., Seki, M., Nishide, H., Uchiyama, I., Kamiya, A., Carninci, P., Hayashizaki, Y., Shinozaki, K., Kohara, Y., and Hasebe, M. 2003. Comparative genomics of Physcomitrella patens gemetophytic transcriptome and Arabidopsis thaliana: Implication for land plant evolution. Proc. Natl. Acad. Sci. USA 100: 8007-8012.(*both authors contributed equally)
(5-2) Candidate gene approaches in shoot development
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The functions of some candidate genes involved in diploid shoot development in angiosperms, such as the KNOX and HD-Zip genes, are being compared with those in the diploid shoot of the fern Ceratopteris and in the haploid shoot of the moss Physcomitrella. Polar auxin transport is indispensable for regular development of the diploid shoot, and investigations of transport in the haploid shoot of Physcomitrella are currently underway. Our preliminary results likely support the de novo hypothesis. |
Sano, R., Juarez, C. M., Hass, B., Sakakibara, K., Ito, M., Banks, JA, and Hasebe, M. 2005. KNOX class of homeobox genes potentially have similar function in both diploid unicellular and multicellular meristems, but not in haploid meristems. Evol. Dev. 7: 69-78.
Sakakibara, K., Nishiyama, T., Sumikawa, N., Kofuji, R., Murata, T. and Hasebe, M. 2003. Involvement of auxin and a homeodomain-leucine zipper I gene in rhizoid development of the moss Physcomitrella patens. Development 130: 4835-4846.
(5-3) Molecular Mechanisms of haploid shoot development
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Our preliminary analyses showed that KNOX genes were not expressed
in Physcomitrella haploid shoot, and auxin polar transport was not detected
in the haplid shoot either. The lack of these two important factors in
diploid shoot development suggests that the moss haploid shoot is regulated
by differnet develomental system from that of vascular plants. To investigate
genes involved in haploid shoot development, we established approximately
20,000 Physcomitrella gene- or enhancer-trap lines, from which lines with
meristem-specific expression were screened. Corresponding genes in three
lines were identified as encoding kinesin-like and uniquitin-like proteins,
and a small molecular protein. The functions of these genes in the meristem
are currently under investigation. Comparison of these genes among land
plants will give new insights on the evoluiton of shoot development. |
Nishiyama, T., Hiwatashi, Y., Sakakibara, K., Kato, M. and Hasebe, M. 2000. Tagged mutagenesis and gene-trap in the moss, Physcomitrella patens by shuttle mutagenesis. DNA Res. 7: 1-9.
Hiwatashi, Y., Nishiyama, T., Fujita, T. and Hasebe, M. 2001. Establishment of gene-trap and enhancer-trap systems in the moss Physcomitrella patens. Plant J. 28: 105-116
(5-4) Candidate gene approaches in reproductive organ
development
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The flower is the reproductive organ in angiosperms, and floral homeotic
genes, such as MADS-box genes and FLO/LEAFY genes, regulate floral organ
identity. To investigate the origin of floral homeotic genes, the functions
of MADS-box genes and the FLO/LEAFY genes in gymnosperms (Gnetum,
Ginkgo, and cycads), a fern (Ceratopteris), a moss (Physcomitrella),
and three green algae (Chara, Coleochaete, and Closterium)
are being analyzed. |
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Floral morphology varies. To determine whether similar molecular mechanisms are widely maintained, in addition to Arabidopsis-type four-whorled flowers, we are analyzing the expression of floral homeotic genes in Magnolia, Nymphaea, and Amborella flowers, in which the floral organs are arranged in spirals, and in Saururus, which has petal-like bracts.(Figure)Amborella (left) and Houttuynia (right) flowers. |
Land plants
Maizel, A., Bush, M. A., Tanahashi, T., Perkovic, J., Kato, M., Hasebe, M., and Weigel, D. 2005. The floral regulator LEAFY evolves by substitutions in the DNA binding domain. Science 308: 260-263.
Gymnosperms
Shindo, S., Sakakibara, K., Sano, R., Ueda, K. and Hasebe, M. 2001. Characterizatin of a FLORICAULA/LEAFY homologue of Gnetum parvifolium, and its implications for the evolution of reproductive organs in seed plants. Int. J. Plant Sci. 162: 1199-1209.
Shindo, S., Ito, M., Ueda, K., Kato, M. and Hasebe, M. 1999. Characterization of MADS genes in the gymnosperm Gnetum parvifolium and its implication on the evolution of reproductive organs in seed plants. Evolution and Development 1 : 180-190.
Ferns
Hasebe, M., Wen, C.-K., Kato, M. and Banks, J.A. 1998. Characterization of MADS homeotic genes in the fern Ceratopteris richardii. Proc. Natl. Acad. Sci. USA 95: 6222-6227.
Mosses
Tanahashi, T., Sumikawa, N., Kato, M., and Hasebe, M. 2005. Diversification of gene function: homologs of the floral regulator FLO/LFY control the first zygotic cell division in the moss Physcomitrella patens. Development 132: 1727-1736.
Charophytes
Tanabe*, Y., Hasebe*, M., Sekimoto, H., Nishiyama, T., Kitani, M., Henschel,
K., MuNnster, T., Theissen, G., Nozaki, H., and Ito, M. 2005. Characterization
of MADS-box genes in charophycean green alga and its implication for the evolution
of MADS-box genes. Proc. Natl. Acad. Sci. USA 102: 2436-2441. (*both authors
contributed equally)
6. Molecular
mechanisms of speciation
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Reproductive isolation is the first step in speciation. To obtain insight
into reproductive isolation, several receptors specifically expressed in
the pollen tube are being studied to screen for the receptors that are involved
in pollen tube guidance. (Figure) pollentube of Arabidopsis stained with DAPI visualizing two sperm nuclei and a pollen tube nucleus. |
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Polyploidization is a major mode of speciation in plants, although the
changes that occur after genome duplication are not well known. Polyploid
species are usually larger than diploids, but the mechanisms responsible
for the size difference are unknown. To investigate these mechanisms, tetraploid
Arabidopsis was established and its gene expression patterns are being compared
to those of diploid wild-type plants using microarrays. (Figure) Leaves of diploid (left) and tetraploid (right) Arabidopsis. |
7. Evolution of cleistogamous in Cardamine
Cardamine flexuosum form both cleistogamous and regular flowers. To investigate the molecular mechanisms underlying the evoluiton of cleistogamous flowers, which evelved many times in flowering plants, comparison of expressed genes between cleitogamous and regular floral primordia using Arabidopsis microarray are on going.
8. Evolution of digestive enzymes in carnivorous plants
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Evolutionary novelties have been essential to the diversification of organisms. One of such novelties is carnivory in plants. Digestive enzymes are excised from the leaves to digest prays, but the origin of the enzyme is unknown. Analyses of digestive enzymes in Nepenthes, Sarracenia, Cephalotus, Pinguicula, and Drosera and their homologs in Arabidopsis are on going. |
9. Color polymorphism of the stag beetle Lamprima
adolphinae
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Lamprima adolphinae has extensive color variation. Genetic analyses of color inheritance are in progress |
