Laboratories

Plant Morphological Dynamics

Prof. Tasaka
Professor
Masao TASAKA
Assistant Professor
Jun ITO
Labs HP
http://bsw3.naist.jp/keihatsu/

Outline of Research and Education

During embryogenesis in higher plants, special tissues called the shoot and root meristems are formed at the upper and lower ends, respectively. After germination, the shoot meristem forms above-ground organs such as leaves, stems and floral organs, while the root meristem produces underground roots. Both genetic controls and diverse external environmental factors such as light or gravity influence the formation of the plant body. By using Arabidopsis thaliana, a model crucifer plant suitable for molecular genetic analyses, we are studying molecular mechanisms that regulate plant development.

Major Research Topics

Polar auxin transport mechanisms

Polar auxin transport is involved in various growth responses including axis formation during embryogenesis, organogenesis, vascular patterning, apical dominance, and tropism. In the process, auxin efflux carriers play a key role. Auxin efflux carriers are localized to the plasma membrane with polarity in one cell and arranged in a uniform orientation in organs and tissues, which allow directional auxin transport through them. We have isolated and identified genes involved in localization of auxin efflux carrier with polarity by molecular genetic methods. The analyses of these genes demonstrate an important role of vesicle trafficking and signaling pathway in the establishment of polar localization of auxin efflux carrier. At present, we attempt to investigate the intercellular molecular network to establish the polarity.

Molecular mechanisms for auxin-dependent gene transcription

Auxin coordinates the transcription of numerous auxin-dependent genes through nuclear auxin receptor. Nuclear auxin receptor regulates the activity of transcription factors to control the synthesis of mRNA by RNA polymerase II. However, precise molecular mechanisms have not been elucidated yet. We are currently focusing on the Mediator complex, which conveys signals from transcription factors to RNA polymerase II machinery and general transcription factors, and seek to understand molecular mechanisms underlying auxin-dependent gene transcription.

Molecular mechanisms for secondary growth

Once the main primary body plans has been established by the activity of the shoot and root apical meristems, some plant species undergo secondary growth. The vascular cambium, a lateral meristem, produces continuously the vascular tissues through secondary growth and drives the radial thickenings of plant organs. Furthermore, during secondary growth another outside lateral meristem, the cork cambium, is formed. In Arabidopsis, secondary growth occurs in stems, roots and hypocotyl. We are focusing on the secondary growth-related lateral meristems, the vascular cambium and the cork cambium, and attempting to elucidate the regulatory mechanisms of secondary growth using Arabidopsis hypocotyl (Fig. 3).

References

  1. Furutani M. et al., Proc Natl Acad Sci USA, 113, 1198-203, 2014
  2. Uchida N. and Tasaka, M. J. Exp. Bot., 64, 5335-43, 2013
  3. Uchida N. et al., Plant Cell Physiol., 53, 343-51, 2012
  4. Uchida N. et al., Proc Natl Acad Sci USA, 109, 6337-42, 2012
  5. Furutani M. et al., Development, 138, 2069-78, 2011
  6. Chung K. et al., Plant Cell Physiol., 52, 1657-64, 2011
  7. Uchida N. et al., Plant Cell Physiol., 52, 804-14, 2011
  8. Uchida N. et al., Plant Cell Physiol., 52, 716-22, 2011
  9. Toyota M. et al., Plant J., 65, 589-599, 2011
  10. Ito J. et al., Plant Cell Physiol., 52, 539-52, 2011
  11. Kato T. et al., Plant Cell Physiol., 51, 333-8, 2010
  12. Ikeyama Y. et al., Plant J., 62, 865-75, 2010
Fig.1 (A) Auxin efflux carriers (green) are localized in the plasma membrane with polarity and auxin is transported to a neighboring cell (orange arrow). (B) Localization of GFP-tagged auxin efflux carrier (green) and presumptive auxin flows (orange arrows) in Arabidopsis embryo.
Fig.1 (A) Auxin efflux carriers (green) are localized in the plasma membrane with polarity and auxin is transported to a neighboring cell (orange arrow). (B) Localization of GFP-tagged auxin efflux carrier (green) and presumptive auxin flows (orange arrows) in Arabidopsis embryo.
Fig.2 Two peptide hormones, EPFL4 and EPFL6, are produced in the endodermal cell layer in the inflorescence stems. These hormones are secreted from the endodermis and received by their receptor called ERECTA in phloem tissues. This ligand-receptor pair regulates the elongation of stems. Mutant plants lacking the receptor or the ligands are shorter than normal Wild-type plants.
Fig.2 A schematic diagram of auxin-dependent transcription: The transcription factor AUXIN RESPONSE FACTOR (ARF) binds to an auxin-responsive element AuxRE in the promoter region of target genes. A mediator complex transmits information from the ARF to RNA polymerase‚Ö°.
Fig.2 Secondary growth in Arabidopsis hypocotyl. Arabidopsis hypocotyl undergoes substantial secondary growth in the stele (red circled area) as a result of the activities of the vascular cambium and the cork cambium.
Fig.3 Secondary growth in Arabidopsis hypocotyl. Arabidopsis hypocotyl undergoes substantial secondary growth in the stele (red circled area) as a result of the activities of the vascular cambium and the cork cambium.
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