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Biomedical subjects

C R Somerville

Publications and source records attributed to C R Somerville.

At least 37 records · Page 2Linked to original sources
PubMed1993

Genetic engineering of commercially useful biosynthetic pathways in transgenic plants.

In many economically important plant species, the chemical composition of one or more non-protein compounds determines the value of the plant and may have an important role in protecting the plant from environmental stress, including pests, drought, salt, temperature and light. A number of potential opportunities exist whereby the range or amount of such valuable compounds can be increased by genetic engineering.

Carbohydrates↗
PubMed1993

Future prospects for genetic modification of the composition of edible oils from higher plants.

It is now routinely possible to introduce genes into many plant species of agronomic significance. This has created new opportunities to genetically engineer higher plants to produce edible fats and oils with predefined fatty acid composition. Because of the chemical diversity of plants, the genes required for synthesis of many different types of lipids exist in nondomesticated species. Thus, it should be possible to modify the storage-lipid composition of crop plants by transferring the relevant genes from the wild species into crop plants. However, although a coherent model now exists for plant-lipid metabolism, a substantial amount of the specific information required to undertake genetic engineering of plant-lipid metabolism is not yet available.

Dietary Fats, Unsaturated↗
PubMed1992

Map-based cloning of a gene controlling omega-3 fatty acid desaturation in Arabidopsis.

A gene from the flowering plant Arabidopsis thaliana that encodes an omega-3 desaturase was cloned on the basis of the genetic map position of a mutation affecting membrane and storage lipid fatty acid composition. Yeast artificial chromosomes covering the genetic locus were identified and used to probe a seed complementary DNA library. A complementary DNA clone for the desaturase was identified and introduced into roots of both wild-type and mutant plants by Ti plasmid-mediated transformation. Transgenic tissues of both mutant and wild-type plants had significantly increased amounts of the fatty acid produced by this desaturase.

Amino Acid Sequence↗
PubMed1992

Gibberellin Is Required for Flowering in Arabidopsis thaliana under Short Days.

Mutants of Arabidopsis thaliana deficient in gibberellin synthesis (ga1-3 and ga1-6), and a gibberellin-insensitive mutant (gai) were compared to the wild-type (WT) Landsberg erecta line for flowering time and leaf number when grown in either short days (SD) or continuous light (CL). The ga1-3 mutant, which is severely defective in ent-kaurene synthesis because it lacks most of the GA1 gene, never flowered in SD unless treated with exogenous gibberellin. After a prolonged period of vegetative growth, this mutant eventually underwent senescence without having produced flower buds. The gai mutant and the "leaky" ga1-6 mutant did flower in SD, but took somewhat longer than WT. All the mutants flowered readily in CL, although the ga1-3 mutant showed some delay. Unlike WT and ga1-3, the gai mutant failed to respond to gibberellin treatment by accelerating flowering in SD. A cold treatment promoted flowering in the WT and gai, but failed to induce flowering in ga1-3. From these results, it appears that gibberellin normally plays a role in initiating flowering of Arabidopsis.

Journal Article↗
PubMed1992

Primary Structure of Cytochrome b(5) from Cauliflower (Brassica oleracea L.) Deduced from Peptide and cDNA Sequences.

Cytochrome b(5) is a microsomal protein that functions as an intermediate electron donor in fatty acid desaturation and other oxidation/reduction reactions. cDNA clones were isolated from cauliflower (Brassica oleracea L.) by using oligonucleotides based on the partial amino acid sequence of the protein. The deduced amino acid sequence of the polypeptide exhibited approximately 30% sequence identity with the homologous protein from vertebrates.

Journal Article↗
PubMed1992

An Arabidopsis mutant defective in the general phenylpropanoid pathway.

Mutants of Arabidopsis deficient in a major leaf phenylpropanoid ester, 2-O-sinapoyl-L-malate, were identified by thin-layer chromatographic screening of methanolic leaf extracts from several thousand mutagenized plants. Mutations at a locus designated SIN1 also eliminate accumulation of the sinapic acid esters characteristic of seed tissues. Because of increased transparency to UV light, the sin1 mutants exhibit a characteristic red fluorescence under UV light, whereas wild-type plants have a blue-green appearance due to the fluorescence of sinapoyl malate in the upper epidermis. As determined by in vivo radiotracer feeding experiments, precursor supplementation studies, and enzymatic assays, the defect in the sin1 mutants appears to block the conversion of ferulate to 5-hydroxyferulate in the general phenylpropanoid pathway. As a result, the lignin of the mutant lacks the sinapic acid-derived components typical of wild-type lignin.

Arabidopsis↗
PubMed1992

Mutations at the Arabidopsis CHM locus promote rearrangements of the mitochondrial genome.

Nuclear recessive mutations at the chloroplast mutator (CHM) locus of Arabidopsis produce a variegated phenotype that is inherited in a non-Mendelian fashion. Molecular analysis of the cytoplasmic genomes of variegated plants from two independent chm mutant lines, using specific chloroplast and mitochondrial probes, showed that the chm mutations reproducibly induce the appearance of specific new restriction fragments in the mitochondrial genome. The presence of these restriction fragments cosegregated with the variegated phenotype in the progeny of crosses between mutant and wild-type plants. Sequence analysis of one of the new restriction fragments found in the variegated plants suggested that it was the product of a rearrangement event involving regions of the mitochondrial genome. Thus, it appears that the CHM locus may encode a protein involved in the control of specific mitochondrial DNA reorganization events.

Arabidopsis↗
PubMed1992

Identification of an operon involved in sulfolipid biosynthesis in Rhodobacter sphaeroides.

Two new mutants of Rhodobacter sphaeroides deficient in sulfolipid accumulation were isolated by directly screening mutagenized cell lines for polar lipid composition by thin-layer chromatography of lipid extracts. A genomic clone which complemented the mutations in these two lines, but not the previously described sulfolipid-deficient sqdA mutant, was identified. Sequence analysis of the relevant region of the clone revealed three, in tandem open reading frames, designated sqdB, ORF2, and sqdC. One of the mutants was complemented by the sqdB gene, and the other was complemented by the sqdC gene. Insertional inactivation of sqdB also inactivated sqdC, indicating that sqdB and sqdC are cotranscribed. The N-terminal region of the 46-kDa putative protein encoded by the sqdB gene showed slight homology to UDP-glucose epimerase from various organisms. The 30-kDa putative protein encoded by ORF2 showed very striking homology to rabbit muscle glycogenin, a UDP-glucose utilizing, autoglycosylating glycosyltransferase. The 26-kDa putative protein encoded by the sqdC gene was not homologous to any protein of known function.

Amino Acid Sequence↗
PubMed1992

Isolation and genetic complementation of a sulfolipid-deficient mutant of Rhodobacter sphaeroides.

All photosynthetic organisms are thought to contain the sulfolipid 6-sulfo-alpha-D-quinovosyl diacylglycerol. However, the pathway of sulfolipid biosynthesis has not been elucidated, and the functional or structural significance of this lipid is not known. Mutants of Rhodobacter sphaeroides deficient in sulfolipid accumulation were isolated by directly screening for altered sulfolipid content. The mutants had no apparent phenotype except for the sulfolipid deficiency. A gene, designated sqdA, which complemented one of the mutations was isolated and characterized. The putative sqdA gene product is a protein with a molecular mass of 33.6 kDa that has no sequence similarity to any enzyme of known function.

Amino Acid Sequence↗
PubMed1991

The role of cytochrome b5 in delta 12 desaturation of oleic acid by microsomes of safflower (Carthamus tinctorius L.).

The electron donors for the membrane-bound fatty acid desaturases of higher plants have not previously been identified. In order to assess the participation of cytochrome b5 in microsomal fatty acid desaturation, the cytoplasmic domain of microsomal cytochrome b5 was purified from Brassica oleracea, and murine polyclonal antibodies were prepared. The IgG fraction from ascites fluid inhibited 62% of NADH-dependent cytochrome c reduction in safflower (Carthamus tinctorius L.) microsomes. These antibodies also blocked desaturation of oleic acid to linoleic acid in lipids of C. tinctorius microsomes by 93%, suggesting that cytochrome b5 is the electron donor for the delta 12 desaturase.

Carbon Radioisotopes↗
PubMed1991

Isolation of a cDNA Clone for Spinach Lipid Transfer Protein and Evidence that the Protein Is Synthesized by the Secretory Pathway.

A cDNA clone encoding a nonspecific lipid transfer protein from spinach (Spinacia oleracea) was isolated by probing a library with synthetic oligonucleotides based on the amino acid sequence of the protein. Determination of the DNA sequence indicated a 354-nucleotide open reading frame which encodes a 118-amino acid residue polypeptide. The first 26 amino acids of the open reading frame, which are not present in the mature protein, have all the characteristics of a signal sequence which is normally associated with the synthesis of membrane proteins or secreted proteins. In vitro transcription of the cDNA and translation in the presence of canine pancreatic microsomes or microsomes from cultured maize endosperm cells indicated that proteolytic processing of the preprotein to the mature form was associated with cotranslational insertion into the microsomal membranes. Because there is no known mechanism by which the polypeptide could be transferred from the microsomal membranes to the cytoplasm, the proposed role of this protein in catalyzing lipid transfer between intracellular membranes is in doubt. Although the lipid transfer protein is one of the most abundant proteins in leaf cells, the results of genomic Southern analysis were consistent with the presence of only one gene. Analysis of the level of mRNA by Northern blotting indicated that the transcript was several-fold more abundant than an actin transcript in leaf and petiole tissue, but was present in roots at less than 1% of the level in petioles.

Journal Article↗
PubMed1990

Purification of adenine phosphoribosyltransferase from Brassica juncea.

Adenine phosphoribosyltransferase was purified from Brassica juncea leaves approximately 4000-fold, to homogeneity. The native enzyme is a homodimer, with a Mr of 54,000. The purification involved (NH4)2SO4 fractionation, differential ultracentrifugation, and anion-exchange, hydrophobic, dye-ligand, and affinity chromatography. The purified enzyme has a pH optimum of 9.15 and a temperature optimum of 60 degrees C. Activity of the enzyme is stimulated by Mg2+ and is inhibited by sulfhydryl reagents. At the optimum pH and 37 degrees C, the apparent Km values for adenine and 5-phosphoribosyl-1-pyrophosphate were 3.8 and 15 microM, respectively. Analysis of the purified protein by isoelectric focusing revealed the presence of two isozymes with approximate isoelectric points of 5.3 and 5.4.

Adenine Phosphoribosyltransferase↗
PubMed1990

Effect of Light Quality and Vernalization on Late-Flowering Mutants of Arabidopsis thaliana.

We have analyzed the response to vernalization and light quality of six classes of late-flowering mutants (fb, fca, fe, fg, ft, and fy) previously isolated following mutagenesis of the early Landsberg race of Arabidopsis thaliana (L.) Heynh. When grown in continuous fluorescent illumination, four mutants (fca, fe, ft, and fy) and the Landsberg wild type exhibited a reduction in both flowering time and leaf number following 6 weeks of vernalization. A significant decrease in flowering time was also observed for all the mutants and the wild type when constant fluorescent illumination was supplemented with irradiation enriched in the red and far red regions of the spectrum. In the most extreme case, the late-flowering phenotype of the fca mutant was completely suppressed by vernalization, suggesting that this mutation has a direct effect on flowering. The fe and fy mutants also showed a more pronounced response than wild type to both vernalization and incandescent supplementation. The ft mutant showed a similar response to that of the wild type. The fb and fg mutants were substantially less sensitive to these treatments. These results are interpreted in the context of a multifactorial pathway for induction of flowering, in which the various mutations affect different steps of the pathway.

Journal Article↗
PubMed1990

A Mutation Causing Imidazolinone Resistance Maps to the Csr1 Locus of Arabidopsis thaliana.

A mutant of Arabidopsis thaliana, two hundred times more resistant to the imidazolinone herbicide imazapyr than wild-type plants, was isolated by direct selection of seedlings from a mutagenized population. Genetic analysis showed that resistance is due to a single dominant nuclear mutation that could not be separated by recombination from a mutation in the CSR1 gene encoding acetohydroxy acid synthase. Acetohydroxy acid synthase activity in extracts isolated from the mutant was 1000-fold more resistant to inhibition by imazapyr than that of the wild type. The resistant enzyme activity cosegregated with whole plant resistance. These data strongly suggest that the mutation is an allele of CSR1 encoding an imazapyr-resistant AHAS.

Journal Article↗
PubMed1990

Three Classes of Abscisic Acid (ABA)-Insensitive Mutations of Arabidopsis Define Genes that Control Overlapping Subsets of ABA Responses.

Wild type and three abscisic acid (ABA)-insensitive mutants of Arabidopsis (ABI1, ABI2, and ABI3) were compared for their ability to respond to ABA for a variety of ABA-inducible responses throughout the life cycle of the plants. The responses tested included effects on seedling growth, proline accumulation in seedlings, ABA-regulated protein synthesis in plantlets, and seed storage protein and lipid synthesis and accumulation. The abi1 and abi2 mutants showed reduced sensitivity to ABA for inhibition of seedling growth, induction of proline accumulation, and alterations in protein synthesis patterns during vegetative growth, but had wild type levels of storage reserves. In contrast, the abi3 mutant had wild type sensitivity for induction of proline accumulation and was only slightly less responsive to ABA with respect to effects on seedling growth and changes in patterns of protein synthesis. The major effects of this mutation were on seed development. Seeds of the abi3 mutant had two-thirds of the wild type level of storage protein and one-third the wild type level of eicosenoic acid, the major fatty acid component of storage lipids in wild type seeds. These results show that none of the abi mutants is insensitive for all ABA-inducible responses and that the abi3 effects are not seed-specific. Comparison of the degree of ABA sensitivity of monogenic mutant lines with that of digenic mutant lines carrying pairwise combinations of the abi mutations suggests that ABA responses in mature seeds are controlled by at least two parallel pathways.

Journal Article↗
PubMed1989

Coidentity of putative amylase inhibitors from barley and finger millet with phospholipid transfer proteins inferred from amino acid sequence homology.

A class of small polypeptides, isolated from seeds of barley and millet, which had been previously identified as putative amylase inhibitors has been found to have striking amino acid sequence identity with phospholipid transfer proteins. In addition, both classes of proteins have the same molecular weight and appear to be produced by proteolytic cleavage of an amino-terminal peptide of similar size. These properties, and the lack of any known activity for the barley protein, suggest that the putative amylase inhibitors are lipid transfer proteins.

Amino Acid Sequence↗
PubMed1988

A Starch Deficient Mutant of Arabidopsis thaliana with Low ADPglucose Pyrophosphorylase Activity Lacks One of the Two Subunits of the Enzyme.

A starch deficient mutant of Arabidopsis thaliana (L.) Heynh. has been isolated in which leaf extracts contain only about 5% as much activity of ADPglucose pyrophosphorylase (EC 2.7.7.27) as the wild type. A single, nuclear mutation at a previously undescribed locus designated adg2 is responsible for the mutant phenotype. Although the mutant contained only 5% as much ADPglucose pyrophosphorylase activity as the wild type, it accumulated 40% as much starch when grown in a 12 hour photoperiod. The mutant also contained about 40% as much starch as the wild type when grown in continuous light, suggesting that the rate of synthesis regulates its steady state accumulation. Immunological analysis of leaf extracts using antibodies against the spinach 54 and 51 kilodalton (kD) ADPglucose pyrophosphorylase subunits indicated that the mutant is deficient in a cross-reactive 54 kD polypeptide and has only about 4% as much as the wild type of a cross-reactive 51 kD polypeptide. This result and genetic studies suggested that adg2 is a structural gene which codes for the 54 kD polypeptide, and provides the first functional evidence that the 54 kD polypeptide is a required component of the native ADPglucose pyrophosphorylase enzyme.

Journal Article↗