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PEPTIDE PLANT HORMONE, PHYTOSULFOKINE 69 Fig. 2. Chemical structure of the purified growth factor. This factor is a sulfated peptide composed of only five amino acids, and due to the presence of sulfate esters, it was named phytosulfokine (PSK). often found in secreted peptides in animals, (Huttner WB. 1982, Niehrs C et al. 1993) but, to date, PSK is the only example of post-translational sulfation of tyrosine in plants. PSK is present, with identical structure, in conditioned medium derived from cell lines of many plants, including dicotyledons and monocotyledons, indicating that it is widely distributed among higher plants. Possible function of PSK Initial cell density is a determining factor in in vitro cellular re-differentiation such as tracheary element (TE) formation, which occur at high frequency under high cell density but are significantly suppressed below threshold densities, suggesting that intercellular signaling is involved in initiation and/or subsequent progress in cellular re-differentiation. (Fukuda H, & Komamine A. 1980) Interestingly, PSK triggers TE differentiation of Zinnia mesophyll cells at nanomolar concentrations.(Matsubayashi Y. et al. 1999) This phenomenon is not a secondary effect caused by increased cell density, because a high proportion of TEs differentiate directly from dispersed mesophyll cells without intervening cell division. It has also been demonstrated that PSK signaling is involved in somatic embryogenesis in a carrot system (Kobayashi T. et al. 1999, Hanai H. et al. 2000), and in adventitious bud formation on callus of Antirrhinum majus. (Yang G. et al. 1999) However, neither cellular re-differentiation nor dedifferentiation can be induced by PSK alone; they require certain ratios and concentrations of auxin and cytokinin in addition to PSK. (Matsubayashi Y. et al. 1999) Whereas PSK triggers TE differentiation of Zinnia mesophyll cells without intervening cell division in a cytokinin-rich medium, it induces cellular dedifferentiation and proliferation in an auxin-rich medium. Neither dedifferentiation nor re-differentiation occurs without PSK. In this context, it is possible that PSK first confers competence to individual cell plants, and that auxin/cytokinin then determines cell fate (Fig. 3). PSK also promotes adventitious root formation on cucumber hypocotyls (Yamakawa S. et al. 1998); it is likely that this organ development is determined by the endogenous auxin/cytokinin level. Genes for PSK precursor proteins Five paralogous genes encoding ≈ 80-amino-acid precursors of PSK have been identified in
70 Yoshikatsu MATSUBAYASHI Fig. 3. Possible mode of action of PSK. PSK confers a competence for dedifferentiation and/or re-differentiation on fully differentiated cells. In this step, no morphological change is observed. After the acquisition of competence, auxin, cytokinin, and other factors determine cell fate. Arabidopsis. (The Arabidopsis Genome Initiative. 2000, Yang H. et al. 2001) Each predicted protein has a probable secretion signal at the N-terminus and a single PSK sequence close to the C- terminus. In addition, there are dibasic amino acid residues immediately upstream from the PSK domain. (Fig. 4) Peptide-hormones and other biologically active peptides are generally synthesized as inactive higher-molecular-weight precursors that must undergo a variety of post-translational processing steps to yield the active peptides. (Harris RB. 1989) PSK mRNAs are detected not only in dedifferentiated callus cells but also in leaves and roots Fig. 4. Alignment of the deduced amino acid sequences of PSK precursor proteins in Arabidopsis. Red box indicate the five-amino-acid PSK domain. Predicted amino terminal signal sequences are underlined and putative processing site immediately upstream from PSK domain are boxed by yellow. Aspartic acid residues on the amino-terminal side of the first tyrosine of PSK domain, one of the most important determinant of the sulfation of PSK precursor, are boxed by blue. Identical amino acid residues are indicated by an asterisk, and similar amino acid residues are indicated by a colon.
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ISSN 0435-1096 Gamma Field Symposia
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The lecturers and the members of th
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KANEKO, T. KARITA, E. KASHIMA, M. K
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TANO, S. TSUCHIDA, Y. TSUTSUMI, N.
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The Symposium Committee Shigeki NAG
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CONTENTS Y. KAMIYA Biosyntheses and
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2 Yuji KAMIYA Fig. 1. Gibberellin b
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4 Yuji KAMIYA using the receptor pr
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6 Yuji KAMIYA Fig. 3. Origin of sid
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8 Yuji KAMIYA References AKIYOSHI,
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10 Yuji KAMIYA SHINOMURA, T. (1997)
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12 Yuji KAMIYA 8’ 8’ 273
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14 Motoyuki ASHIKARI, Hironori ITOH
Page 27 and 28: 16 Motoyuki ASHIKARI, Hironori ITOH
Page 37 and 38: 26 Atsuhiro OKA and how their signa
Page 39 and 40: 28 Atsuhiro OKA At almost the same
Page 41 and 42: 30 Atsuhiro OKA division for xylem
Page 43 and 44: 32 Atsuhiro OKA the RR domain in th
Page 45 and 46: 34 Atsuhiro OKA Fig. 4. Cross-talk
Page 47 and 48: 36 Atsuhiro OKA OKA, A., SAKAI, H.
Page 49 and 50: 38 Atsuhiro OKA ARR4 PHYB PHYBP
Page 51 and 52: Gamma Field Symposia, No. 42, 2003
Page 53 and 54: ETHYLENE-SIGNALING PATHWAY 43 signa
Page 55 and 56: ETHYLENE-SIGNALING PATHWAY 45 The f
Page 57 and 58: ETHYLENE-SIGNALING PATHWAY 47 Snf3p
Page 59 and 60: ETHYLENE-SIGNALING PATHWAY 49 In sp
Page 61 and 62: ETHYLENE-SIGNALING PATHWAY 51
Page 63 and 64: Gamma Field Symposia, No. 42, 2003
Page 65 and 66: MECHANISM OF BRASSINOSTEROID SIGNAL
Page 77: 68 Yoshikatsu MATSUBAYASHI are grow
Page 81 and 82: 72 Yoshikatsu MATSUBAYASHI Fig. 5.
Page 83 and 84: 74 Yoshikatsu MATSUBAYASHI Fig. 6.
Page 85 and 86: 76 Yoshikatsu MATSUBAYASHI 33. Yang
Page 87 and 88: 78 Yoshikatsu MATSUBAYASHI GUS
Page 89 and 90: 80 BRI1
Page 91 and 92: 82 BRI 10
Page 93 and 94: 84 100
Page 95 and 96: 86 PSK 23 BIL1/CFP
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