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GA SIGNAL TRANSDUCTION 19 interacting with the SCF GID2 complex. In gid2, the phosphorylation of SLR1 also occurs following GA3 treatment but the degradation does not occur due to the loss-of-function of the GID2 protein, and consequently the SLR1 protein is accumulated (Sasaki et al. 2003). This model is consistent with previous findings in yeast, mammals and plant, that is, phosphorylation of a target protein triggers the degradation process (Deshaies 1999). A recent publication describes the inhibition of barley SLN1 protein degradation by a proteasome inhibitor (Fu et al. 2002). This supports the notion that the SLR1 protein is degraded through the proteasome. Conclusions and Prospects Based on the results described in this review, we conclude that SLR1 functions as a molecular switch in GA signaling in rice plants. Actually, whether GA activity occurs or not is readily determined by the absence or presence, respectively, of the functional SLR1 protein in the nucleus. GID2 encodes an F-box protein that may be a component of an SCF ubiquitin-ligase complex. The fact that GID2 encodes an F-box protein and SLR1 is highly accumulated in the gid2 mutant led us to speculate that GA-dependent degradation of SLR1 is mediated by the SCF GID2 complex. This is supported by the finding that a phosphorylated form of the SLR1 protein is also accumulated in gid2. So far, there are previous reports that phosphorylation of target proteins triggers SCF-mediated degradation, our results also indicate that GA-dependent phosphorylation of SLR1 triggers the ubiquitin-mediated degradation (Fig. 3), in a similar manner to the SCFmediated pathway in plant, yeast and animals. On the other hand, the mechanism by which SLR1 perceives the GA signal is still unknown. It is possible that the other GA-insensitive dwarf gene, GID1, modifies the molecular structure of the SLR1 protein. Unlike other plant hormones, the GA receptor has not yet been identified. Identification of new mutants associated with GA signaling will be important for elucidating the mechanism of the GA signal transduction pathway, including identification of the GA receptor. As in the case of Fig. 4 Putative model for the GA signal transduction pathway in rice.
20 Motoyuki ASHIKARI, Hironori ITOH, Miyako UEGUCHI and Makoto MATSUOKA SLR1, there is a tendency for the rice genome to have a single gene associated with GA signaling. This non-redundant relationship of GA signal-related genes in rice plants should facilitate the study of the GA signal transduction pathway. References 1. Ashikari, M., Wu, J., Yano, M., Sasaki, T. and Yoshimura, A. (1999) Rice gibberellin-insensitive dwarf mutant gene Dwarf 1 encodes the alpha-subunit of GTP-binding protein. PNAS 96: 10284-10289. 2. Chandler, P. M. (1988) Hormonal regulation of gene expression in the “slender” mutant of barley (Hordeum vulgare L.). Planta 175: 115-120. 3. Chandler, P. M., Marion, P. A, Ellis, M. and Gubler, F. (2002) Mutants at the Slender1 locus of barley cv Himalaya. Molecular and physiological characterization. Plant Physiol 129: 181-190. 4. Croker, S. J., Hedden, P., Lenton, J. R. and Stoddart, J. (1990) Comparison of gibberellin in normal and slender barley seedlings. Plant Physiol 94: 194-200. 5. Dashaies, R. J. (1999) SCF and Cullin/Ring H2-based ubiquitin ligases. Annu. Rev. Cell Dev. Biol. 15: 435-467. 6. Dill, A., Jung, H. S., Sun, T. P. (2001) The DELLA motif is essential for gibberellin-induced degradation of RGA. PNAS 98: 14162-14167. 7. Fleck, B. and Harberd, N. P. (2002) Evidence that the Arabidopsis nuclear gibberellin signaling protein GAI is not destabilized by gibberellin. Plant Journal. 32: 935-947. 8. Foster, C. A. (1977) Slender: an accelerated extension growth mutant of barley. Barley Genetics Newsletter 7: 24-27. 9. Fu, X., Richards, D. E., Ait-Ali, T., Hynes, L. W., Ougham, H., Peng, J. and Harberd, N. P. (2002) Gibberellin-mediated proteasome-dependent degradation of the barley DELLA protein SLN1 repressor. Plant Cell 14: 3191-3200. 10. Gubler, F., Chandler, P. M., White, R. G., Llewellyn, D. J. and Jacobsen, J. V. (2002) Gibberellin signaling in barley aleurone cells. Control of SLN1 and GAMYB expression. Plant Physiol 129: 191-200. 11. Harberd, N. P. and Freeling, M. (1989) Genetics of dominant gibberellin-insensitive dwarfism in maize. Genetics 121: 827-838. 12. Hedden, P. and Phillips, A. L. (2000) Gibberellin metabolism: new insights revealed by the genes. Trend Plant Sci 5: 523-530. 13. Hooley, R. (1994) Gibberellin: perception, transduction and responses. Plant Mol Bio 26: 1529-1555. 14. Ikeda, A., Ueguchi-Tanaka, M., Sonoda, Y., Kitano, H., Koshioka, M., Futsuhara, Y., Matsuoka, M. and Yamaguchi, J. (2001) slender rice, a constitutive gibberellin response mutant, is caused by a null mutation of the SLR1 gene, an ortholog of the height-regulating gene GAI/RGA/RHT/D8. Plant Cell 13: 999-1010. 15. Itoh, H., Ueguchi-Tanaka, M., Sentoku, N., Kitano, H., Matsuoka, M. and Kobayashi, M. (2001) Cloning and functional analysis of two gibberellin 3 beta -hydroxylase genes that are differently expressed during the growth of rice. PNAS 98: 8909-8914. 16. Itoh, H., Ueguchi-Tanaka, M., Sato, Y., Ashikari, M. and Matsuoka, M. (2002) The gibberellin signaling pathway is regulated by the appearance and disappearance of SLENDER RICE1 in nuclei. Plant Cell 14: 57-70. 17. Koornneef, M., Elgersma, A., Hanhart, C. J., van Loenen-Martinet, E. P., van Rign, L., and Zeevaart, J. A. D. (1985) A gibberellin insensitive mutant of Arabidopsis thaliana. Physiol Plant 65: 33-39. 18. Lanahan, M. B. and Ho, T. H. D. (1988) Slender barley: A constitutive gibberellin-response mutant. Planta 175: 107-114. 19. Laurenzio, D. L., Wysocka-Diller, J., Malamy, J. E., Pysh, L., Helariutta, Y., Freshour, G., Hahn, M. G., Feldmann, K. A. and Benfey, P. N. (1996) The SCARECROW gene regulates an asymmetric cell division
Page 1 and 2: ISSN 0435-1096 Gamma Field Symposia
Page 3 and 4: The lecturers and the members of th
Page 5 and 6: KANEKO, T. KARITA, E. KASHIMA, M. K
Page 7 and 8: TANO, S. TSUCHIDA, Y. TSUTSUMI, N.
Page 9 and 10: The Symposium Committee Shigeki NAG
Page 11 and 12: CONTENTS Y. KAMIYA Biosyntheses and
Page 13 and 14: 2 Yuji KAMIYA Fig. 1. Gibberellin b
Page 15 and 16: 4 Yuji KAMIYA using the receptor pr
Page 17 and 18: 6 Yuji KAMIYA Fig. 3. Origin of sid
Page 19 and 20: 8 Yuji KAMIYA References AKIYOSHI,
Page 21 and 22: 10 Yuji KAMIYA SHINOMURA, T. (1997)
Page 23 and 24: 12 Yuji KAMIYA 8’ 8’ 273
Page 25 and 26: 14 Motoyuki ASHIKARI, Hironori ITOH
Page 29: 18 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 and 78: 68 Yoshikatsu MATSUBAYASHI are grow
Page 79 and 80: 70 Yoshikatsu MATSUBAYASHI Fig. 3.
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72 Yoshikatsu MATSUBAYASHI Fig. 5.
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74 Yoshikatsu MATSUBAYASHI Fig. 6.
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76 Yoshikatsu MATSUBAYASHI 33. Yang
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78 Yoshikatsu MATSUBAYASHI GUS
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80 BRI1
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82 BRI 10
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84 100
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86 PSK 23 BIL1/CFP
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