研究概要

RESEARCH: Evolution of development in land plants (2) Evolution of developmetal genes in land plants II

Shizuka Koshimizu (graduate student in SOKENDAI [The Graduate University for Advanced Studies]) and Assoc. Prof. Takashi Murata

We cloned MADS-box genes and characterized their expression patterns in the fern C. richardii (Hasebe et al. 1998 Proc. Natl. Acad. Sci. USA 95: 6222), the moss P. patens (Henschel et al. 2002 Mol. Biol. Evol. 19: 801), and three charophycean green algae (Tanabe et al. 2005 Proc. Natl. Acad. Sci. USA 102: 2436). We also cloned and characterized FLORICAULA/LEAFY (FLO/LFY) homologsin C. richardii (Himi et al. 2003 J. Mol. Evol. 53: 387) and P. patens (Tanahashi et al. 2005 Development 132: 1727; Maizel et al. 2005 Science 308: 260). These studies suggested that the following sequential changes occurred in the evolution of reproductive organs:

  1. Origin of MIKC-type MADS-box genes in the green plant lineage and subsequent divergence of MIKCc-type and MIKC*-type MADS-box genes (Henschel et al. 2002 Mol. Biol. Evol. 19: 801; Kofuji et al. 2003 Mol. Biol. Evol. 20: 1963).
  2. MIKCc-type MADS-box genes likely functioned during reproductive cell differentiation in a haploid generation at the common ancestor of land plants (Tanabe et al. 2005 Proc. Natl. Acad. Sci. USA 102: 2436).
  3. The number of MADS-box genes was extensively increased in the vascular plant lineage (Hasebe et al. 1998 Proc. Natl. Acad. Sci. USA 95: 6222).
  4. FLO/LFY homologs regulated zygotic cell divisions in a diploid generation and their function was not restricted in reproductive organ development (Tanahashi et al. 2005 Development 132: 1727).
  5. A single amino acid change in the FLO/LFY homolog in the last common ancestor of vascular plants likely caused the regulation of MADS-box genes by FLO/LFY homologs (Maizel et al. 2005 Science 308: 260), and their relationship was retained in gymnosperms and angiosperms (Shindo et al. 1999 Evol. Dev. 1: 180; Shindo et al. 2001 Int. J. Plant Sci. 162: 1199).
  6. A-, B-, and C-type MADS-box gene orthologs had likely diverged before the branching of ferns and seed plants (Hasebe et al. 1998 Proc. Natl. Acad. Sci. USA 95: 6222).

Although we showed that MADS-box genes of the charophycean green algae were expressed during reproductive cell differentiation, their function was not clear because of the lack of transformation systems in those algae. To investigate the ancestral function of MADS-box genes in the earlier stages of land plant evolution, we are in the process of functional characterization of MADS-box genes in P. patens. Ms. Shizuka Koshimizu mainly works in this project with advices of Assos. Prof. Takashi Murata.