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Phytochromes and gene expression
trends in plant science research news from Brassica napus specific for the hydroxyl group at position 22 of select BRs. Some functional conservation has been found between human hydroxysteroid sulphotransferase and the BR sulphotransferase. Sulphation is an effective means of inactivating steroid hormones in both plants and animals. A revolution in evolution
Our appreciation for the biochemistry, physiology and evolution of plant secondary metabolism has certainly improved since natural products were first described as waste metabolites6. The sustained efforts and combined strengths of phytochemists, biochemists and molecular biologists interested in plant secondary metabolism have breathed new life into an old and well-established discipline. The awesome potential of the Arabidopsis genome project, together with powerful
molecular technologies, are changing our approach to phytochemical research. The new findings and ideas presented at the meeting will impact on our fundamental perceptions about the metabolism, evolution, physiology and ecology of plants. Peter J. Facchini Dept of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 (tel 11 403 220 7651; fax 11 403 289 9311; e-mail [email protected]) References 1 Kahn, R.A. et al. (1999) Substrate specificity of the cytochrome P450 enzymes CYP79A1 and CYP71E1 involved in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench, Arch. Biochem. Biophys. 363, 9–18
2 Prescott, A.G. and John, P. (1996) Dioxygenases: molecular structure and role in plant metabolism, Annu. Rev. Plant Physiol. Plant Mol. Biol. 47, 245–271 3 Ibrahim, R.K., Bruneau, A. and Bantignies, B. (1998) Plant O-methyltransferases: molecular analysis, common signature and classification, Plant Mol. Biol. 36, 1–10 4 Li, J. and Chory, J. (1997) A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction, Cell 90, 929–938 5 Vogt, T. et al. (1997) Are the characteristics of betanidin glucosyltransferases from cell-suspension cultures Dorotheanthus bellidiformis indicative of their phylogenetic relationship with flavonoid glucosyltransferases? Planta 203, 349–361 6 Ellis, B.E. (1997) Metabolism of defense and communication, in Plant Metabolism (Dennis, D.T. et al., eds), pp. 148–160, Addison Wesley Longman, Essex, UK
literature focus
Less lignin is more cellulose Hu, W-J., Harding, S.A., Lung, J., Popko, J.L., Ralph, J., Stokke, D.D., Tsai, C.J. and Chiang, V.L. (1999) Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees, Nat. Biotechnol. 17, 808Ð812 Lignin provides plants with a rigid cell wall, but it hinders the processing of timber for cellulosebased products and must be separated from cellulose at great financial and environmental cost. Recent research on the lignin biosynthetic pathway has therefore focused on the potential to manipulate the expression of key enzymes in the pathway to ease lignin extraction. In this context, Hu et al. used antisense inhibition to down regulate expression of Pt4Cl1, an important lignin biosynthesis gene in developing xylem of Aspen trees. The resulting transgenic trees accumulated up to 45% less structural lignin, but, unlike previous studies in which reduced lignin content was accompanied by collapsed cell walls and reduced growth, structural integrity was maintained at the whole plant level. Indeed, the plant response to reduced lignin production was marked by a 15% increase in the accumulation of cellulose. The compensatory regulation of lignin and cellulose biosynthesis had the surprising effect of enhancing the growth rates of the transgenic aspen. These results provide an exciting new direction for developing strategies to manipulate the lignin biosynthetic pathway and the productivity of trees. 384
October 1999, Vol. 4, No. 10
Phytochromes and gene expression Ni, M., Tepperman, J.M. and Quail, P.H. (1999) Binding of phytochrome B to its nuclear signalling partner PIF3 is reversibly induced by light, Nature 400, 781Ð784 One of the most keenly researched topics in plant biology is how plants sense their local light environment. The authors of this paper have analysed the interaction between phytochrome B and the nuclear-localized phytochrome-interacting factor 3 (PIF3), a putative transcriptional regulator. The assay system relied on the binding of radiolabelled domains of phytochrome B to matrix-immobilized PIF3. Full-length phytochrome B binds to PIF3 only after photoconversion to its active (Pfr) form by
a red-light pulse. A subsequent far-red pulse results in reconversion to its inactive form and rapid dissociation from PIF3. Individually, the N-terminal chromophore binding domain and C-terminal dimerization domain show relatively weak binding to PIF3, and the two appear to act synergistically to determine the strength of binding. These results further extend the phytochrome signalling pathway from the cytoplasm to the nucleus and demonstrate the potential to link photoactivation to gene expression.
Alternative splicing and mitochondrial import Kubo, N., Harada, K., Hirai, A. and Kadowaki, K-I. (1999) A single nuclear transcript encoding mitochondrial RPS14 and SDHB of rice is processed by alternative splicing: common use of the same mitochondrial targeting signal for different proteins, Proc. Natl. Acad. Sci. U. S. A. 96, 9207Ð9211 This paper presents evidence that two proteins that function in the mitochondria of rice, but that are otherwise unrelated, have transferred to the nuclear genome and share sequences for targeting to mitochondria. The two genes are rps14, encoding ribosomal protein RPS14, and sdhb, encoding succinate dehydrogenase subunit B. Analysis of their cDNAs revealed that sdhb and rps14 have identical 59 sequences. The mitochondrial genome still retains a gene with homology to rps14, but it contains internal stop codons, whereas there is no equivalent
sdhb sequence. Genomic sequencing revealed that the coding sequence for SDHB is divided into two exons, and, remarkably, the coding sequence for RPS14 is located between these exons. The gene transcripts appear to be carried by a single mRNA with alternative splicing giving rise to the two proteins. These results suggest that genetransfer of sdhb occurred prior to the migration of rps14, and that rps14 was subsequently able to transfer into an existing nuclear gene and make use of its mitochondrial targeting sequence.
1360 - 1385/99/$ Ð see front matter © 1999 Elsevier Science Ltd. All rights reserved.
Our appreciation for the biochemistry, physiology and evolution of plant secondary metabolism has certainly improved since natural products were first described as waste metabolites6. The sustained efforts and combined strengths of phytochemists, biochemists and molecular biologists interested in plant secondary metabolism have breathed new life into an old and well-established discipline. The awesome potential of the Arabidopsis genome project, together with powerful
molecular technologies, are changing our approach to phytochemical research. The new findings and ideas presented at the meeting will impact on our fundamental perceptions about the metabolism, evolution, physiology and ecology of plants. Peter J. Facchini Dept of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 (tel 11 403 220 7651; fax 11 403 289 9311; e-mail [email protected]) References 1 Kahn, R.A. et al. (1999) Substrate specificity of the cytochrome P450 enzymes CYP79A1 and CYP71E1 involved in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench, Arch. Biochem. Biophys. 363, 9–18
2 Prescott, A.G. and John, P. (1996) Dioxygenases: molecular structure and role in plant metabolism, Annu. Rev. Plant Physiol. Plant Mol. Biol. 47, 245–271 3 Ibrahim, R.K., Bruneau, A. and Bantignies, B. (1998) Plant O-methyltransferases: molecular analysis, common signature and classification, Plant Mol. Biol. 36, 1–10 4 Li, J. and Chory, J. (1997) A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction, Cell 90, 929–938 5 Vogt, T. et al. (1997) Are the characteristics of betanidin glucosyltransferases from cell-suspension cultures Dorotheanthus bellidiformis indicative of their phylogenetic relationship with flavonoid glucosyltransferases? Planta 203, 349–361 6 Ellis, B.E. (1997) Metabolism of defense and communication, in Plant Metabolism (Dennis, D.T. et al., eds), pp. 148–160, Addison Wesley Longman, Essex, UK
literature focus
Less lignin is more cellulose Hu, W-J., Harding, S.A., Lung, J., Popko, J.L., Ralph, J., Stokke, D.D., Tsai, C.J. and Chiang, V.L. (1999) Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees, Nat. Biotechnol. 17, 808Ð812 Lignin provides plants with a rigid cell wall, but it hinders the processing of timber for cellulosebased products and must be separated from cellulose at great financial and environmental cost. Recent research on the lignin biosynthetic pathway has therefore focused on the potential to manipulate the expression of key enzymes in the pathway to ease lignin extraction. In this context, Hu et al. used antisense inhibition to down regulate expression of Pt4Cl1, an important lignin biosynthesis gene in developing xylem of Aspen trees. The resulting transgenic trees accumulated up to 45% less structural lignin, but, unlike previous studies in which reduced lignin content was accompanied by collapsed cell walls and reduced growth, structural integrity was maintained at the whole plant level. Indeed, the plant response to reduced lignin production was marked by a 15% increase in the accumulation of cellulose. The compensatory regulation of lignin and cellulose biosynthesis had the surprising effect of enhancing the growth rates of the transgenic aspen. These results provide an exciting new direction for developing strategies to manipulate the lignin biosynthetic pathway and the productivity of trees. 384
October 1999, Vol. 4, No. 10
Phytochromes and gene expression Ni, M., Tepperman, J.M. and Quail, P.H. (1999) Binding of phytochrome B to its nuclear signalling partner PIF3 is reversibly induced by light, Nature 400, 781Ð784 One of the most keenly researched topics in plant biology is how plants sense their local light environment. The authors of this paper have analysed the interaction between phytochrome B and the nuclear-localized phytochrome-interacting factor 3 (PIF3), a putative transcriptional regulator. The assay system relied on the binding of radiolabelled domains of phytochrome B to matrix-immobilized PIF3. Full-length phytochrome B binds to PIF3 only after photoconversion to its active (Pfr) form by
a red-light pulse. A subsequent far-red pulse results in reconversion to its inactive form and rapid dissociation from PIF3. Individually, the N-terminal chromophore binding domain and C-terminal dimerization domain show relatively weak binding to PIF3, and the two appear to act synergistically to determine the strength of binding. These results further extend the phytochrome signalling pathway from the cytoplasm to the nucleus and demonstrate the potential to link photoactivation to gene expression.
Alternative splicing and mitochondrial import Kubo, N., Harada, K., Hirai, A. and Kadowaki, K-I. (1999) A single nuclear transcript encoding mitochondrial RPS14 and SDHB of rice is processed by alternative splicing: common use of the same mitochondrial targeting signal for different proteins, Proc. Natl. Acad. Sci. U. S. A. 96, 9207Ð9211 This paper presents evidence that two proteins that function in the mitochondria of rice, but that are otherwise unrelated, have transferred to the nuclear genome and share sequences for targeting to mitochondria. The two genes are rps14, encoding ribosomal protein RPS14, and sdhb, encoding succinate dehydrogenase subunit B. Analysis of their cDNAs revealed that sdhb and rps14 have identical 59 sequences. The mitochondrial genome still retains a gene with homology to rps14, but it contains internal stop codons, whereas there is no equivalent
sdhb sequence. Genomic sequencing revealed that the coding sequence for SDHB is divided into two exons, and, remarkably, the coding sequence for RPS14 is located between these exons. The gene transcripts appear to be carried by a single mRNA with alternative splicing giving rise to the two proteins. These results suggest that genetransfer of sdhb occurred prior to the migration of rps14, and that rps14 was subsequently able to transfer into an existing nuclear gene and make use of its mitochondrial targeting sequence.
1360 - 1385/99/$ Ð see front matter © 1999 Elsevier Science Ltd. All rights reserved.