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58 Takeshi NAKANO, Shigeo YOSHIDA and Tadao ASAMI Fig. 5 Screened bil (Brz-insensitive-long hypocotyl) mutants of Arabidopsis. bil1 mutants with 3 M Brz had hypocotyls as long as those of wild-type plants grown on unsupplemented medium. and the bes1 mutant has the same nucleotide substitution (Yin et al., 2002). The plant-specific gene family encompassing BZR1, BES1 and BIL1 encodes novel phosphoproteins containing a putative nuclear localization signal. The BIL1/BZR1:CFP fusion protein localizes mainly to the cytoplasm and also to the nucleus at low levels, but treatment with brassinosteroids results in a significant increase of BIL1/BZR1:CFP levels in the nucleus within thirty minutes. In contrast, a BZR1:CFP protein containing the mutation localizes continuously to the nucleus (Wang et al., 2002). Then, the mutants felt that brassinosteroid signaling is on in every time, and these can showed wild-type like phenotype in brassinosteroid deficient condition. These results suggest that BIL1/BZR1 and BES1 is a key component in brassinosteroid signaling from the cell surface to the nucleus (Fig. 6). The phenotypes of the bzr1/bil1 and bes1 Brz-resistance and bri1-suppressor mutants, respectively, are very strong, with the resistant mutant just like wild-type plants in appearance, even though it is severely deficient in brassinosteroids. These mutants, the mutant alleles of which are both dominants, resulted from the substitution of just one amino acid as compared to the wild type. Overexpression of the BZR1 or BES1 wild-type genes via the CaMV 35S promoter resulted in only weak resistance against brassinosteroid deficiency (Wang et al., 2002, Yin et al., 2002). These results suggest that bzr1/bil1 and bes1 mutants would be difficult to identify from activationtagged pools of plants in the background of a mutant deficient in brassinosteroids, such as det2 or dwf4. An alternative method is to induce point mutations by chemical treatment of brassinosteroiddeficient mutants. The most widely-used method to identify point mutations is genomic walking, performed using backcrosses with another ecotype. The screening is best performed on recombinant F2 plants, to allow identification of the brassinosteroid-deficiency mutation as a
MECHANISM OF BRASSINOSTEROID SIGNALING 59 Fig. 6 Mechanism of brassinosteroid signaling conducted by BIL1/BZR1/BES1 protein. Treatment with brassinosteroids results in movement of BIL1/BZR1/BES1 from cytosol to nucleus. BIL1/BZR1/BES1 protein containing the mutation localizes continuously to the nucleus. homozygous det2/det2 plant, and not as det2/DET2 or DET2/DET2 plants. This is because distinguishing between putative brassinosteroid-signaling mutants with a det2/det2 homozygous background and det2/DET2 or DET2/DET2 plants with no mutation is very difficult, since they would all have a phenotype of resistance against brassinosteroid deficiency. Identifying a suppressor mutant resulting from a point mutation might also be challenging. These predictions suggest that the combination of Brz and a simple point mutation in the wild-type Colombia ecotype can allow rapid identification of crucial signaling proteins. This role for Brz will be a great contribution to plant science. bil5, Brz-insensitive-long hypocotyl5 We have identified a recessive mutant, bil5, from seeds that received fast neutron treatment. The length of the hypocotyls of this mutant on medium containing Brz is less than that of bil1-D, but at least twice that of the wild type (Fig. 5). Interestingly, adult bil5 plants have pale green, thin stems, thin leaves and a shortened stem length. The dwarf-like phenotype is distinct from the brassinosteroid-deficient dwarf phenotype, and the pale-green leaves of bil5 are in contrast to the dark-green leaves of brassinosteroid-deficient mutants. A preliminary analysis has shown that chloroplast gene expression is lower in bil5 than in the wild type. At least in darkness, brassinosteroid is a negative regulator of chloroplast development. BIL5 may be a key protein in the brassinosteroid regulation of chloroplasts. In addition, the bil5 shortened stem phenotype can be rescued by humidity of 85% or above and light conditions of less than 25 µE, and its stomata have lowered responses to ABA and tend to stay opened. This observation suggests that the
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ISSN 0435-1096 Gamma Field Symposia
Page 3 and 4:
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
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 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
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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
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Page 77 and 78: 68 Yoshikatsu MATSUBAYASHI are grow
Page 79 and 80: 70 Yoshikatsu MATSUBAYASHI Fig. 3.
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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